Copper-catalyzed tandem radical amination/1, 2-carbon migration of allylic alcohols: Direct access to α-quaternary-β-amino ketones


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本文作者相关文章
	Jiaqiong Sun

	Guangfan Zheng

	Yongmei Fu

	Qiao Zhang

	Yimin Wang

	Qian Zhang

	Yan Li

	Qian Zhang

Jiaqiong Sun, Guangfan Zheng, Yongmei Fu, Qiao Zhang, Yimin Wang, Qian Zhang^†, Yan Li, Qian Zhang

Jilin Province Key Laboratory of Organic Functional Molecular Design & Synthesis, Faculty of Chemistry, Northeast Normal University, Changchun 130024, Jilin, China

Received 4 September 2017; Accepted 15 September 2017; Published 5 January 2018

^* Corresponding author. Yan Li, Tel: +86-431-85099759; E-mail: liy078@nenu.edu.cn;
Qian Zhang, Tel: +86-431-85099206; E-mail: zhangq651@nenu.edu.cn

^† These authors are different persons

Foundation item: This work was supported by the National Natural Science Foundation of China (21372041), Changbai Mountain Scholarship Program, and the Fundamental Research Funds for the Central Universities (2412016KJ006)

Abstract: A novel nitrogen-centered radical-induced 1, 2-carbon migration reaction of allylic alcohols has been developed. This method provides easy access to a variety of α-quaternary-β-amino ketones under mild reaction conditions. The reaction has a wide substrate scope and operational simplicity. Mechanistic studies suggest that 1, 2-carbon migration is induced by regioselective nitrogen-centered radical addition to the alkene unit.

Key words: Allylic alcohols Nitrogen-centered radicals 1, 2-Carbon migration α-Quaternary-β-amino ketones N-F regent

铜催化的烯丙醇自由基胺化/1, 2-碳迁移串联反应:一步构建含α-季碳中心的β-胺基酮

孙佳琼, 郑光范, 付永梅, 张乔, 王义敏, 张茜^†, 李燕, 张前^†

东北师范大学化学学院, 吉林省有机功能分子设计与合成重点实验室, 吉林长春 130024

收稿日期：2017-09-04. 接受日期：2017-09-15. 出版日期：2018-01-05

基金项目：国家自然科学基金（21372041）；长白山学者奖励计划；中央高校基本科研业务费专项资金（2412016KJ006）

通讯联系人：李燕, 电话: (0431)85099759;电子信箱: liy078@nenu.edu.cn;
张前, 电话: (0431)85099206;电子信箱: zhangq651@nenu.edu.cn

摘要：烯丙醇类化合物是非常重要的有机合成砌块.近年来，自由基或阳离子对烯丙醇类化合物的加成引发的1，2-碳迁移反应迅速发展，被认为是合成含α-季碳中心的β-羰基化合物最有效的策略之一.目前，烯丙醇的官能团化/1，2-碳迁移反应取得了很好的成果，各种官能团化反应，比如卤化、三氟甲基化、硫化、膦化和芳基化等，已经顺利实现.但是，烯丙醇类化合物的胺化/1，2-碳迁移串联反应研究较少.这可能是由于竞争的亲核胺化反应存在导致的.因此，发展烯丙醇类化合物的胺化串联反应值得期待.我们及其他课题组以N-氟代双苯磺酰亚胺（NFSI）作为有效的自由基氮源，实现了烯烃或炔烃的自由基胺化官能团化反应.研究表明，在铜催化温和条件下即可生成金属稳定的氮中心自由基物种.据此，我们认为，在温和条件下有效产生氮中心自由基是实现烯丙醇自由基胺化/1，2-碳迁移串联反应的关键.在前期工作基础上，本文利用NFSI及其衍生物作为有效的自由基胺化试剂，实现了铜催化烯丙醇类化合物的自由基胺化/1，2-碳迁移串联反应，直接构建重要的含α-季碳中心的β-胺基酮骨架. 本文合成了24个不同官能团取代的β-胺基酮衍生物.反应中芳环上取代基的电子效应和空间效应表现并不明显.当芳基对位连有卤素、烷氧基、芳基、烷基时，或者邻位和间位甲基取代的1-（1-芳基烯基）环丁醇均可以与NFSI顺利反应，以中等至较高的产率得到相应的含α-季碳中心的β-胺基酮.氧杂环丁醇、取代的环丁醇类化合物，5元、6元及非环状的苯基烯丙醇类化合物均适用于该反应，生成相应的目标化合物.同时，我们也扩展了胺化试剂的范围，除NFSI衍生物外，单取代的NFHSO₂Ph类型氮源也可以有效发生自由基胺化/1，2-碳迁移串联反应，生成目标产物.另外，扩大反应物的量至5mmol，反应不受影响，仍能以90%的产率生成β-胺基酮衍生物.最后，通过控制实验捕捉到反应中生成的苄基自由基中间体，表明该反应经历氮中心自由基对烯丙醇烯烃双键的区域选择性加成引发的1，2-碳迁移串联反应. 总之，本文以N-F试剂作为自由基胺化试剂，利用铜催化体系发展了烯丙醇类化合物的自由基胺化/1，2-碳迁移串联反应，一步合成了重要的β-胺基酮类化合物.该反应条件温和，底物适用范围宽泛，官能团兼容性较好，合成了一系列链状、环状及螺环的含有α-季碳中心的β-胺基酮衍生物.据我们所知，这是首例将NHFSO₂Ph类型N-F试剂作为自由基氮源的反应.

关键词：烯丙醇氮中心自由基 1, 2-碳迁移反应含α-季碳中心的β-胺基酮 N-F试剂

1 Introduction

Allylic alcohols are among the most versatile building blocks in organic synthesis, and their 1, 2-carbon migration induced by radical or cation addition, e.g., in the semipinacol rearrangement, is a widely used and powerful method for constructing α-quaternary-β-functionalized carbonyl compounds [1-3]. Such compounds are important in organic synthesis, e.g., in the total synthesis of natural products; therefore the development of more efficient methods for their synthesis is needed [4-9]. Much effort has been devoted to investigating methods for the functionalization of allylic alcohols [10-43], such as halogenation [10-18], trifluoromethylation [19-26], sulfonylation [27], phosphorylation [28], and arylation [29-31]. These methods enable direct synthesis of various α-quaternary-β-functionalized ketones (Scheme 1, (a)). However, the aminative 1, 2-carbon migration of allylic alcohols is challenging because of direct competition from nucleophilic substitution. In 2008, Tu and coworkers [44] developed a tandem aziridination/ rearrangement reaction of allylic alcohols using a nitrene equivalent (Scheme 1, (b)). In 2014, the same group reported a radical azidative 1, 2-carbon migration reaction of allylic silyl ethers (Scheme 1, (c)) [45]. Progress has been made in this field, but the development of an effective aminative carbonation of allylic alcohols via 1, 2-carbon migration is still needed. We reasoned that facile generation of a nitrogen-centered radical under mild reaction conditions could be the key to this domino reaction.

Scheme 1. Addition to C=C bond induced 1, 2-carbon migration of allylic alcohols and derivatives.

Radical amination has emerged as a powerful tool for the synthesis of a range of bioactive nitrogen-containing molecules [46, 47]. Studer [49, 50], Kanai [51], and our group [53-58] have shown that N-fluorobenzenesulfonamide (NFSI) is an efficient and versatile nitrogen radical source for aminative functionalization of alkenes and alkynes [48-61]. Recently, Liu and coworkers [62] reported a novel copper-catalyzed enantioselective aminocyanation of alkenes using this reagent. It has been shown that a sterically hindered metal-stabilized nitrogen radical can be generated from NFSI under mild reaction conditions. On the basis of these pioneering studies, we reasoned that a radical semipinacol rearrangement of allylic alcohols could be triggered by addition of an in situ-generated nitrogen-centered radical to the alkene unit. While this manuscript was being prepared, Zhang and coworkers [63] reported a copper-catalyzed amination-induced 1, 2-rearrangement of allylic alcohols. Here, we report a novel radical amination/ 1, 2-carbon migration cascade, using an inexpensive copper catalyst, that enables rapid assembly of α-quaternary-β-amino ketones from readily available allylic alcohols (Scheme 1).

2 Experimental

2.1 General

All reagents were purchased from commercial suppliers and used without further purification. The reactions were monitored using thin-layer chromatography on 0.25 mm pre-coated silica-gel plates. UV light was used for visualization. Melting points (mps) were measured using a Büchi B-540 apparatus. ¹H NMR spectra were recorded at 25 ℃ using a Bruker 600 or Varian 500 MHz instrument. ¹³C NMR spectra were recorded at 25 ℃ using a Bruker 150 or Varian 125 MHz instrument. Chemical shifts (δ) are given in parts per million (ppm) relative to the residual solvent signals (CHCl₃, 7.26 ppm for ¹H NMR and 77.00 ppm for ¹³C NMR). Coupling constants (J) are given in hertz. The letters m, s, d, t, and q stand for multiplet, singlet, doublet, triplet, and quartet, respectively. High-resolution mass spectrometry (HRMS) was performed using a Brucker micrOTOF instrument. The allylic alcohols 1 were synthesized using a previously published procedure [14, 30].

2.2 General procedure for synthesis of compounds 3 and 4

An allylic alcohol (0.2 mmol), N-F reagent (0.3 mmol), Cu[(CH₃CN)₄PF₆] (0.02 mmol, 7.5 mg), BC (0.02 mmol, 7.2 mg), and anhydrous CHCl₃ (2 mL) were added to a flame-dried reaction tube equipped with a magnetic stirring bar in a nitrogen-filled glove box. The tube was sealed with a screw-cap and removed from the glove-box. The reaction mixture was stirred at 60 ℃ for 24.0 h. When the reaction was finished, the reaction mixture was cooled to room temperature and quenched with water. The mixture was extracted with dichloromethane (3 × 5.0 mL). The combined organic phases were dried over anhydrous Na₂SO₄ and the solvent was evaporated under vacuum. The residue was purified using column chromatography (petroleum ether/ethyl acetate 15:1 (v/v)) to give the corresponding product.

2.3 Spectral data for products

3a. White solid, mp 143-144 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.76 (d, J = 7.8 Hz, 4H), 7.64 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.37 (dd, J = 7.8, 0.6 Hz, 2H), 7.34-7.31 (m, 2H), 7.26-7.24 (m, 1H), 4.25 (d, J = 16.2 Hz, 1H), 4.05 (d, J = 16.2 Hz, 1H), 2.60 (dd, J = 13.2, 6.0 Hz, 1H), 2.48-2.42 (m, 1H), 2.26 (dd, J = 19.2, 9.0 Hz, 1H), 2.18-2.11 (m, 1H), 1.97-1.92 (m, 1H), 1.63-1.56 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 217.8, 139.2, 138.3, 134.0, 129.0, 128.9, 128.6, 127.5, 127.0, 58.1, 53.3, 36.6, 32.3, 18.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₄H₂₃NNaO₅S₂ ([M + Na]⁺) 492.0910, found 492.0914.

3b. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.73 (d, J = 7.8 Hz, 4H), 7.64 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.32-7.28 (m, 4H), 4.21 (d, J = 16.8 Hz, 1H), 4.00 (d, J = 16.2 Hz, 1H), 2.57 (dd, J = 13.2, 5.4 Hz, 1H), 2.49-2.44 (m, 1H), 2.26 (dd, J = 19.2, 9.0 Hz, 1H), 2.20-2.13 (m, 1H), 1.99-1.95 (m, 1H), 1.61-1.54 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.4, 138.3, 137.7, 134.1, 133.6, 129.1, 129.0, 128.6, 128.6, 57.6, 53.8, 36.5, 32.3, 18.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₄H₂₂ClNNaO₅S₂ ([M + Na]⁺) 526.0520, found 526.0529.

3c. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.74 (d, J = 7.8 Hz, 4H), 7.64 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.36-7.34 (m, 2H), 7.03-6.99 (m, 2H), 4.22 (d, J = 16.2 Hz, 1H), 4.00 (d, J = 16.2 Hz, 1H), 2.58 (dd, J = 13.2, 6.0 Hz, 1H), 2.50-2.44 (m, 1H), 2.26 (dd, J = 19.2, 8.4 Hz, 1H), 2.18-2.13 (m, 1H), 1.99-1.94 (m, 1H), 1.62-1.54 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.6, 162.0 (J = 245.9 Hz), 138.3, 134.8 (J = 3.2 Hz), 134.1, 129.0, 128.9 (J = 8.1 Hz), 128.6, 115.8 (J = 21.2 Hz), 57.5, 53.9, 36.6, 32.5, 18.5. HRMS (ESI-TOF) (m/z): Calcd. for C₂₄H₂₂FNNaO₅S₂ ([M + Na]⁺) 510.0816, found 510.0820.

3d. White solid, mp 120-121 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.75 (d, J = 7.8 Hz, 4H), 7.63 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.29-7.26 (m, 2H), 6.86-6.84 (m, 2H), 4.22 (d, J = 16.8 Hz, 1H), 4.02 (d, J = 16.2 Hz, 1H), 3.77 (s, 3H), 2.56 (dd, J = 13.2, 6.0 Hz, 1H), 2.44-2.39 (m, 1H), 2.24 (dd, J = 19.2, 8.4 Hz, 1H), 2.13-2.08 (m, 1H), 1.95-1.90 (m, 1H), 1.61-1.57 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.7, 158.9, 138.4, 134.0, 130.8, 128.9, 128.6, 128.2, 114.3, 57.3, 55.2, 53.9, 36.5, 32.3, 18.5. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₆S₂ ([M + Na]⁺) 522.1016, found 522.1024.

3e. Yellow solid, mp 117-118 ℃. ¹H NMR (500 MHz, CDCl₃) δ 7.76 (d, J = 7.5 Hz, 4H), 7.64 (t, J = 7.5 Hz, 2H), 7.55 (d, J = 8.0 Hz, 4H), 7.50-7.41 (m, 8H), 7.34 (t, J = 7.5 Hz, 1H), 4.28 (d, J = 16.5 Hz, 1H), 4.09 (d, J = 16.5 Hz, 1H), 2.65 (dd, J = 13.0, 5.5 Hz, 1H), 2.52-2.46 (m, 1H), 2.30 (dd, J = 19.5, 9.0 Hz, 1H), 2.21-2.13 (m, 1H), 2.01-1.95 (m, 1H), 1.68-1.63 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 217.7, 140.3, 140.2, 138.3, 138.1, 134.0, 128.9, 128.8, 128.6, 127.6, 127.5, 127.5, 126.9, 57.8, 53.9, 36.6, 32.2, 18.7. HRMS (ESI-TOF) (m/z): Calcd. for C₃₀H₂₇NNaO₅S₂ ([M + Na]⁺) 568.1223, found 568.1231.

3f. White solid, mp 142-143 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.76 (d, J = 7.8 Hz, 4H), 7.64 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.25 (d, J = 8.4 Hz, 2H), 7.13 (d, J = 7.8 Hz, 2H), 4.23 (d, J = 16.2 Hz, 1H), 4.02 (d, J = 16.2 Hz, 1H), 2.58 (dd, J = 13.2, 6.0 Hz, 1H), 2.44-2.39 (m, 1H), 2.31 (s, 3H), 2.24 (dd, J = 19.2, 8.4 Hz, 1H), 2.15-2.04 (m, 1H), 1.95-1.91 (m, 1H), 1.63-1.57 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.8, 138.4, 137.2, 136.0, 134.0, 129.7, 128.9, 128.6, 126.9, 57.7, 53.9, 36.5, 32.2, 20.9, 18.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₅S₂ ([M + Na]⁺) 506.1066, found 506.1075.

3g. White solid, mp 165-166 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.77 (d, J = 7.8 Hz, 4H), 7.64 (t, J = 7.8 Hz, 2H), 7.48 (t, J = 7.8 Hz, 4H), 7.22 (t, J = 7.8 Hz, 1H), 7.18 (d, J = 7.8 Hz, 1H), 7.14 (s, 1H), 7.06 (d, J = 7.2 Hz, 1H), 4.25 (d, J = 16.8 Hz, 1H), 4.04 (d, J = 16.2 Hz, 1H), 2.58 (dd, J = 13.2, 6.0 Hz, 1H), 2.45-2.40 (m, 1H), 2.32 (s, 3H), 2.25 (dd, J = 19.2, 9.0 Hz, 1H), 2.15-2.08 (m, 1H), 1.96-1.91 (m, 1H), 1.64-1.56 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.8, 139.1, 138.6, 138.5, 134.0, 128.9, 128.9, 128.7, 128.2, 127.7, 124.0, 58.0, 54.0, 36.6, 32.2, 21.6, 18.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₅S₂ ([M + Na]⁺) 506.1066, found 506.1075.

3h. White solid, mp 137-138 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.84-7.83 (m, 4H), 7.63 (t, J = 7.8 Hz, 2H), 7.51-7.48 (m, 4H), 7.26 (d, J = 8.4 Hz, 1H), 7.17 (d, J = 4.2 Hz, 2H), 7.13-7.09 (m, 1H), 4.39 (d, J = 16.2 Hz, 1H), 4.23 (d, J = 16.2 Hz, 1H), 2.76 (dd, J = 13.8, 6.0 Hz, 1H), 2.49 (s, 3H), 2.33-2.27 (m, 1H), 2.25-2.19 (m, 1H), 2.09-2.02 (m, 1H), 1.89-1.84 (m, 1H), 1.71-1.62 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 216.5, 138.8, 137.7, 135.6, 133.9, 133.6, 128.9, 128.8, 128.3, 127.7, 126.1, 58.5, 52.8, 36.1, 32.2, 22.1, 18.0. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₅S₂ ([M + Na]⁺) 506.1066, found 506.1073.

3i. White solid, mp 81-82 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.80 (dd, J = 8.4, 0.6 Hz, 4H), 7.66 (t, J = 7.2 Hz, 2H), 7.53-7.49 (m, 4H), 7.41-7.39 (m, 2H), 7.36-7.34 (m, 2H), 7.31-7.28 (m, 1H), 4.77 (d, J = 10.2 Hz, 1H), 4.43 (d, J = 10.8 Hz, 1H), 4.34 (d, J = 16.8 Hz, 1H), 4.21 (d, J = 16.2 Hz, 1H), 4.01 (d, J = 17.4 Hz, 1H), 3.73 (d, J = 16.8 Hz, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 213.0, 138.1, 137.4, 134.3, 129.2, 129.1, 128.6, 128.0, 126.7, 73.7, 70.2, 55.9, 52.0. HRMS (ESI-TOF) (m/z): Calcd. for C₂₃H₂₁NNaO₆S₂ ([M + Na]⁺) 494.0702, found 494.0702.

3j. White solid. ¹H NMR (500 MHz, CDCl₃) δ 7.78 (d, J = 8.0 Hz, 1.5H), 7.69 (d, J = 7.5 Hz, 2.5H), 7.62 (t, J = 7.5 Hz, 2H), 7.48-7.43 (m, 6H), 7.37 (t, J = 7.5 Hz, 1H), 7.32-7.26 (m, 4H), 7.24-7.17 (m, 3H), 4.34-4.15 (m, 1H), 4.08-4.03 (m, 1H), 3.81-3.74 (m, 0.6H), 3.51-3.45 (m, 0.7H), 3.16-3.11 (m, 0.3H), 2.93-2.82 (m, 1H), 2.73-2.49 (m, 2H), 2.35-2.29 (m, 0.3H). ¹³C NMR (125 MHz, CDCl₃) δ 217.0, 216.1, 143.0, 142.5, 142.5, 139.2, 138.3, 137.7, 134.1, 134.1, 129.2, 129.0, 128.8, 128.8, 128.6, 128.5, 128.4, 127.7, 127.1, 126.9, 126.9, 126.8, 126.6, 126.4, 59.7, 57.1, 56.0, 53.9, 45.6, 44.8, 42.8, 39.8, 38.4, 37.6. HRMS (ESI-TOF) (m/z): Calcd. for C₃₀H₂₇NNaO₅S₂ ([M + Na]⁺) 568.1223, found 568.1208.

3k. Yellow solid, mp 175-176 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.91 (d, J = 7.8 Hz, 4H), 7.65 (t, J = 7.2 Hz, 2H), 7.52 (t, J = 7.2 Hz, 4H), 7.21-7.17 (m, 3H), 6.97-6.96 (m, 1H), 4.77 (t, J = 7.2 Hz, 1H), 3.62 (dd, J = 15.0, 7.2 Hz, 1H), 2.79 (dd, J = 15.0, 7.8 Hz, 1H), 2.67-2.62 (m, 1H), 2.34-2.28 (m, 1H), 2.28-2.25 (m, 1H), 2.21-2.18 (m, 1H), 2.14-2.10 (m, 1H), 2.01-1.98 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 215.3, 144.4, 140.8, 139.5, 134.0, 128.9, 127.4, 127.0, 124.2, 122.5, 70.6, 63.5, 38.5, 36.8, 34.8, 18.9. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₃NNaO₅S₂ ([M + Na]⁺) 504.0910, found 504.0905.

3l. Yellow solid, mp 148-149 ℃. ¹H NMR (500 MHz, CDCl₃) δ 7.72-7.71 (m, 4H), 7.61 (t, J = 7.5 Hz, 2H), 7.47-7.43 (m, 4H), 7.34 (t, J = 7.5 Hz, 2H), 7.28-7.25 (m, 1H), 7.23-7.21 (m, 2H), 4.74 (d, J = 16.0 Hz, 1H), 3.87 (d, J = 16.0 Hz, 1H), 2.89-2.86 (m, 1H), 2.40-2.36 (m, 1H), 2.26-2.19 (m, 1H), 2.17-2.11 (m, 1H), 1.83-1.76 (m, 2H), 1.70-1.62 (m, 1H), 1.56-1.50 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 209.9, 139.9, 138.8, 133.8, 129.1, 128.8, 128.7, 127.3, 127.1, 57.1, 54.06, 40.0, 31.4, 26.0, 21.0. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₅S₂ ([M + Na]⁺) 506.1066, found 506.1068.

3m. White solid, mp 173-174 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.65-7.64 (m, 4H), 7.59 (t, J = 7.8 Hz, 2H), 7.42 (t, J = 7.8 Hz, 4H), 7.29-7.23 (m, 3H), 7.20-7.18 (m, 2H), 4.48 (d, J = 16.2 Hz, 1H), 4.28 (d, J = 16.2 Hz, 1H), 2.75 (dd, J = 14.4, 10.2 Hz, 1H), 2.57-2.47 (m, 2H), 2.25 (dd, J = 15.0, 8.4 Hz, 1H), 1.74-1.69 (m, 2H), 1.65-1.58 (m, 2H), 1.51-1.49 (m, 2H). ¹³C NMR (150 MHz, CDCl₃) δ 213.4, 140.9, 138.8, 133.7, 128.8, 128.7, 128.6, 128.3, 127.2, 59.7, 55.3, 42.6, 31.7, 30.7, 25.5, 24.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₆H₂₇NNaO₅S₂ ([M + Na]⁺) 520.1223, found 520.1232.

3n. White solid, mp 189-190 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.56 (t, J = 7.8 Hz, 6H), 7.39 (t, J = 7.2 Hz, 4H), 7.35-7.31 (m, 6H), 7.24 (d, J = 6.6 Hz, 4H), 4.98 (s, 2H), 1.98 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ 206.2, 139. 2, 138.2, 133.5, 130.6, 128.7, 128.6, 128.3, 127.7, 66.9, 53.8, 27.7. HRMS (ESI-TOF) (m/z): Calcd. for C₂₈H₂₅NNaO₅S₂ ([M + Na]⁺) 542.1066, found 542.1054.

3o. Orange solid, mp 90-91 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.65 (dd, J = 8.4, 1.2 Hz, 2H), 7.61 (d, J = 7.8 Hz, 4H), 7.58-7.55 (m, 4H), 7.48 (t, J = 7.2 Hz, 2H), 7.39 (d, J = 8.4 Hz, 4H), 7.37-7.35 (m, 6H), 7.24 (d, J = 2.4 Hz, 2H), 5.04 (d, J = 15.6 Hz, 1H), 4.98 (d, J = 16.2 Hz, 1H), 2.05 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ 206.1, 140.3, 140.1, 139.1, 138.4, 137.3, 133.6, 131.2, 130.5, 128.9, 128.8, 128.6, 128.4, 127.7, 127.6, 127.0, 126.8, 66.7, 53.4, 27.8. HRMS (ESI-TOF) (m/z): Calcd. for C₃₄H₂₉NNaO₅S₂ ([M + Na]⁺) 618.1379, found 618.1379.

4a. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.78-7.76 (m, 4H), 7.50-7.48 (m, 4H), 7.35-7.31 (m, 4H), 7.28-7.25 (m, 1H), 4.20 (d, J = 16.8 Hz, 1H), 4.09 (d, J = 16.8 Hz, 1H), 2.58 (dd, J = 13.2, 6.6 Hz, 1H), 2.36-2.24 (m, 2H), 2.15-2.09 (m, 1H), 1.97-1.92 (m, 1H), 1.64-1.56 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.5, 141.0, 138.7, 136.7, 130.2, 129.3, 129.1, 127.6, 127.0, 58.0, 53.8, 36.45, 32.4, 18.5. HRMS (ESI-TOF) (m/z): Calcd. for C₂₄H₂₁Cl₂NNaO₅S₂ ([M + Na]⁺) 560.0130, found 560.0120.

4b. Pale yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.75-7.73 (m, 2H), 7.66 (d, J = 8.4 Hz, 2H), 7.53-7.50 (m, 2H), 7.43-7.41 (m, 2H), 7.38-7.36 (m, 2H), 7.34-7.31 (m, 2H), 7.27-7.24 (m, 1H), 4.22 (d, J = 16.8 Hz, 1H), 4.07 (d, J = 16.8 Hz, 1H), 2.61 (dd, J = 13.2, 6.0 Hz, 1H), 2.44-2.38 (m, 1H), 2.26 (dd, J = 19.2, 9.0 Hz, 1H), 2.16-2.09 (m, 1H), 1.97-1.92 (m, 1H), 1.62-1.55 (m, 1H), 1.36 (s, 9H). ¹³C NMR (150 MHz, CDCl₃) δ 217.7, 158.4, 140.7, 139.1, 136.9, 135.2, 130.1, 129.1, 129.0, 128.7, 127.5, 127.0, 126.0, 58.1, 53.8, 36.5, 35.3, 32.4, 31.0, 18.5. HRMS (ESI-TOF) (m/z): Calcd. for C₂₈H₃₀ClNNaO₅S₂ ([M + Na]⁺) 582.1146, found 582.1132.

4c. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.83 (d, J = 7.8 Hz, 2H), 7.78 (dd, J = 9.0, 4.8 Hz, 2H), 7.66 (t, J = 7.2 Hz, 1H), 7.52 (t, J = 7.8 Hz, 2H), 7.37-7.31 (m, 4H), 7.26 (t, J = 7.2 Hz, 1H), 7.15 (t, J = 8.4 Hz, 2H), 4.22 (d, J = 16.2 Hz, 1H), 4.07 (d, J = 16.2 Hz, 1H), 2.59 (dd, J = 13.2, 6.0 Hz, 1H), 2.43-2.38 (m, 1H), 2.26 (dd, J = 19.2, 9.0 Hz, 1H), 2.17-2.11 (m, 1H), 1.97-1.92 (m, 1H), 1.63-1.57 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.7, 165.9 (J = 165.9 Hz), 139.1, 138.4, 134.3, 134.1, 131.7 (J = 9.6 Hz), 129.0 (J = 4.7 Hz), 128.7, 127.5, 127.0, 116.2 (J = 22.7 Hz), 58.0, 53.8, 36.5, 32.3, 18.5. HRMS (ESI-TOF) (m/z): Calcd. for C₂₄H₂₂FNNaO₅S₂ ([M + Na]⁺) 510.0816, found 510.0822.

4d. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.79 (d, J = 7.2 Hz, 2H), 7.65-7.60 (m, 3H), 7.49 (t, J = 7.8 Hz, 2H), 7.37 (d, J = 7.2 Hz, 2H), 7.32 (t, J = 7.2 Hz, 2H), 7.27-7.24 (m, 3H), 4.22 (d, J = 16.8 Hz, 1H), 4.04 (d, J = 16.8 Hz, 1H), 2.60 (dd, J = 13.2, 6.0 Hz, 1H), 2.47 (dd, J = 13.2, 7.2 Hz, 1H), 2.43 (s, 3H), 2.26 (dd, J = 19.2, 8.4 Hz, 1H), 2.19-2.13 (m, 1H), 1.96-1.94 (m, 1H), 1.61-1.58 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 217.8, 145.2, 139.4, 138.6, 135.4, 133.9, 129.5, 129.0, 128.9, 128.7, 128.7, 127.4, 127.1, 58.1, 53.9, 36.7, 32.3, 21.6, 18.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₅H₂₅NNaO₅S₂ ([M + Na]⁺) 506.1066, found 506.1075.

4e. White solid, mp 292-293 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.57 (t, J = 7.8 Hz, 1H), 7.43-7.41 (m, 2H), 7.36-7.32 (m, 4H), 7.27-7.25 (m, 3H), 6.95 (s, 2H), 4.25 (d, J = 16.8 Hz, 1H), 4.09 (d, J = 16.2 Hz, 1H), 2.86-2.80 (m, 1H), 2.67 (dd, J = 13.2, 6.0 Hz, 1H), 2.44-2.39 (m, 1H), 2.37 (s, 3H), 2.34 (s, 6H), 2.34-2.31 (m, 1H), 2.10-2.06 (m, 1H), 1.66-1.59 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 218.5, 143.9, 141.4, 140.1, 136.6, 134.0, 133.7, 132.2, 129.0, 128.7, 128.2, 127.4, 127.2, 58.2, 54.2, 36.9, 33.0, 22.6, 21.1, 18.9. HRMS (ESI-TOF) (m/z): Calcd. for C₂₇H₂₉NNaO₅S₂ ([M + Na]⁺) 534.1379, found 534.1389.

4f. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.73 (dd, J = 8.4, 1.2 Hz, 2H), 7.53 (t, J = 7.2 Hz, 1H), 7.45 (t, J = 7.8 Hz, 2H), 7.32-7.30 (m, 2H), 7.27-7.24 (m, 3H), 4.89 (t, J = 7.2 Hz, 1H), 3.25 (dd, J = 13.2, 6.6 Hz, 1H), 3.19 (dd, J = 13.2, 6.6 Hz, 1H), 2.57-2.53 (m, 1H), 2.38-2.31 (m, 2H), 2.26-2.19 (m, 1H), 1.99-1.93 (m, 1H), 1.79-1.72 (m, 1H). ¹³C NMR (150 MHz, CDCl3) δ 219.2, 139.8, 136.8, 132.5, 129.0, 129.0, 127.7, 126.8, 126.6, 57.7, 49.3, 37.4, 31.9, 18.3. HRMS (ESI-TOF) (m/z): Calcd. for C₁₈H₁₉NNaO₃S ([M + Na]⁺) 352.0978, found 352.0986.

4g. Yellow solid, mp 148-149 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.72-7.70 (m, 2H), 7.32 (t, J = 7.8 Hz, 2H), 7.29-7.25 (m, 3H), 7.11 (t, J = 8.4 Hz, 2H), 4.77 (t, J = 7.2 Hz, 1H), 3.24 (dd, J = 13.2, 6.6 Hz, 1H), 3.19 (dd, J = 13.2, 6.6 Hz, 1H), 2.57-2.53 (m, 1H), 2.38-2.30 (m, 2H), 2.29-2.21 (m, 1H), 2.00-1.94 (m, 1H), 1.80-1.72 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 219.3, 165.1 (J = 253.0 Hz), 136.7, 135.9 (J = 3.15 Hz), 129.6 (J = 9.3 Hz), 129.1, 127.8, 126.6, 116.3 (J = 22.3 Hz), 57.6, 49.4, 37.4, 32.1, 18.3. HRMS (ESI-TOF) (m/z): Calcd. for C₁₈H₁₈FNNaO₃S ([M + Na]⁺) 370.0884, found 370.0892.

4h. Yellow liquid. ¹H NMR (600 MHz, CDCl₃) δ 7.64-7.62 (m, 2H), 7.41-7.38 (m, 2H), 7.32-7.29 (m, 2H), 7.27-7.24 (m, 3H), 5.00 (t, J = 6.6 Hz, 1H), 3.25 (dd, J = 13.2, 6.6 Hz, 1H), 3.19 (dd, J = 13.2, 6.6 Hz, 1H), 2.56-2.53 (m, 1H), 2.37-2.20 (m, 3H), 1.99-1.93 (m, 1H), 1.79-1.71 (m, 1H). ¹³C NMR (150 MHz, CDCl₃) δ 219.3, 138.9, 138.3, 136.6, 129.3, 129.0, 128.3, 127.8, 126.6, 57.6, 49.4, 37.4, 32.1, 18.3. HRMS (ESI-TOF) (m/z): Calcd. for C₁₈H₁₈ClNNaO₃S ([M + Na]⁺) 386.0588, found 386.0597.

4i. White solid, mp 145-146 ℃. ¹H NMR (600 MHz, CDCl₃) δ 7.65-7.64 (m, 2H), 7.46-7.44 (m, 2H), 7.32-7.26 (m, 5H), 4.75 (t, J = 6.6 Hz, 1H), 3.26-3.21 (m, 1H), 3.18 (dd, J = 13.2, 6.6 Hz, 1H), 2.58-2.55 (m, 1H), 2.42-2.38 (m, 1H), 2.37-2.31 (m, 1H), 2.27-2.20 (m, 1H), 2.00-1.94 (m, 1H), 1.80-1.71 (m, 1H), 1.32 (s, 9H). ¹³C NMR (150 MHz, CDCl₃) δ 219.3, 156.3, 136.9, 136.7, 129.0, 127.7, 126.7, 126.0, 57.8, 49.3, 37.4, 35.0, 31.8, 31.0, 18.3. HRMS (ESI-TOF) (m/z): Calcd. for C₂₂H₂₇NNaO₃S ([M + Na]⁺) 408.1604, found 408.1611.

6 White solid, mp 241-242 ℃. ¹H NMR (500 MHz, CDCl₃) δ 8.08-8.07 (m, 4H), 7.88-7.86 (m, 2H), 7.67 (t, J = 7.5 Hz, 2H), 7.61 (t, J = 7.5 Hz, 1H), 7.56 (t, J = 7.5 Hz, 4H), 7.48 (t, J = 7.5 Hz, 2H), 5.19 (s, 2H), 1.61 (s, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 190.8, 139.3, 134.4, 134.0, 133.9, 128.9, 128.8, 127.9, 53.6. HRMS (ESI-TOF) (m/z): Calcd. for C₂₀H₁₇NNaO₅S₂ ([M + Na]⁺) 438.0440, found 438.0440.

3 Results and discussion

Our previous work explicitly showed that interactions between a copper salt stabilized by a nitrogen-containing bidentate ligand and NFSI could efficiently generate a nitrogen radical [53, 54]. We chose 1-(1-phenylvinyl)cyclobutanol (1a, 0.2 mmol) as a model substrate and Cu[(CH₃CN)₄PF₆] (10 mol%)/ neocuproine (L1, 10 mol%) as the catalytic system to test the feasibility of the designed transformation in the presence of NFSI in CHCl₃ at 50 ℃ in a nitrogen atmosphere. The expected reaction proceeded smoothly to give the corresponding product 3a in 75% yield (Table 1, entry 1). The effect of the solvent was investigated. The data show that dichloromethane, 1, 2-dichloroethane, and CH₃NO₂ decrease the reaction efficiency (Table 1, entries 2-4), and tetrahydrofuran, dimethylformamide, and toluene were unsuitable (Table 1, entries 5-7) for this transformation. When the temperature was increased from 50 to 60 ℃, 3a was obtained in 80% yield (Table 1, entry 8), but further increases or decreases in the temperature did not increase the yield (Table 1, entries 9 and 10). Investigation of the use of other copper salts, i.e., Cu[(CH₃CN)₄BF₄], CuCN, CuTc, and CuCl, showed that Cu[(CH₃CN)₄PF₆] was the best catalyst (Table 1, entries 11-14). Ligands L2-L5 were screened; a satisfactory yield, i.e., 93% was achieved when bathocuproine (L2) was used (Table 1, entries 15-18).

Table 1 Optimization of reaction conditions ^{a, b}.


Entry	Catalyst	Solvent	Ligand	t (^oC)	Yield (%)
1	Cu[(CH₃CN)₄PF₆]	CHCl₃	L1	50	75
2	Cu[(CH₃CN)₄PF₆]	DCM	L1	50	63
3	Cu[(CH₃CN)₄PF₆]	DCE	L1	50	73
4	Cu[(CH₃CN)₄PF₆]	CH₃NO₂	L1	50	56
5	Cu[(CH₃CN)₄PF₆]	Toluene	L1	50	trace
6	Cu[(CH₃CN)₄PF₆]	THF	L1	50	0
7	Cu[(CH₃CN)₄PF₆]	DMF	L1	50	0
8	Cu[(CH₃CN)₄PF₆]	CHCl₃	L1	60	80
9	Cu[(CH₃CN)₄PF₆]	CHCl₃	L1	80	80
10	Cu[(CH₃CN)₄PF₆]	CHCl₃	L1	30	51
11	Cu[(CH₃CN)₄BF₄]	CHCl₃	L1	60	51
12	CuCN	CHCl₃	L1	60	61
13	CuTc	CHCl₃	L1	60	57
14	CuCl	CHCl₃	L1	60	70
15	Cu[(CH₃CN)₄PF₆]	CHCl₃	L2	60	93
16	Cu[(CH₃CN)₄PF₆]	CHCl₃	L3	60	18
17	Cu[(CH₃CN)₄PF₆]	CHCl₃	L4	60	21
18	Cu[(CH₃CN)₄PF₆]	CHCl₃	L5	60	22
^a General reaction conditions: 1a (0.2 mmol), NFSI (1.5 equiv.), catalyst (10 mol%), ligand (10 mol%), solvent (2 mL), 24 h in nitrogen atmosphere. ^b Yields were determined after isolation of products using column chromatography.

Table 1
Optimization of reaction conditions ^{a, b}.

With the optimized conditions in hand, we investigated the reaction scope and generality (Table 2). A range of 1-(1-arylvinyl)cyclobutanols 1 bearing electron-withdrawing and -donating substituents at the para position were all suitable, producing the desired α-quaternary-β-amino ketones 3a-3f in 65%-95% yields. Halogen atoms were tolerated (3b and 3c), which offers opportunities for further transformations. The structure of 3a was confirmed using X-ray analysis (for the crystal structure of 3a to see CCDC 1560578). The efficiencies of the reactions of 1-(1-arylvinyl)cyclobutanols with a methyl substituent at the ortho, meta, or para position (1f-1h, 73%, 56%, and 40%, respectively) decreased with increasing steric hindrance by the methyl group. Oxacyclobutanol was a compatible substrate and afforded 3i in 85% yield. A substrate with a phenyl group on the cyclobutanol moiety reacted smoothly, affording 3j in 91% yield and with a 2:1 diastereoselectivity ratio. An indene-substituted 1-(1-arylvinyl) cyclobutanol 1k also reacted to afford the spiro β-amino ketone 3k in 66% yield, with excellent diastereoselectivity. The five-and six-membered ring substrates 1l-1m, which lack ring strain, were also viable substrates, although the product yields were low. Suitable allylic alcohols are not limited to cyclic ones. Noncyclic tertiary allylic alcohols (3n and 3o) also showed high reactivities. The synthetic utility of the reaction was investigated by performing a gram-scale reaction between 1a and NFSI (Scheme 2). The desired product 3a was isolated in good yield (90%).

Table 2
Allylic alcohol substrate scope ^{a, b}.

Scheme 2. Gram-scale preparation of 3a.

The generality of this aminative 1, 2-carbon migration reaction was examined by screening amination sources. Different NFSI derivatives were first investigated under the standard reaction conditions (Table 3). NFSI derivatives bearing both electron-donating and -withdrawing substituents at the para position (2a-2d) all reacted smoothly with 1-(1-phenylvinyl)cyclobutanol (1a), and the corresponding products 4a-4d were isolated in 60%-96% yields. The sterically hindered trimethylenyl-substituted N-fluoroarenesulfonamide 2e was also tolerated in this transformation, giving 4e in 49% yield. It is worth noting that the mono-substituted amidation reagents NHFSO₂Ar 2f-2i were also suitable, affording products 4f-4i in 47%-64% yield. To the best of our knowledge, this is the first example of the use of a NHFSO₂Ar-type N-F reagent as a radical amination source.

Table 3
Scope of amination source ^{a, b}.

Radical inhibition experiments were performed to clarify the reaction mechanism (Scheme 3). Addition of 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (2.0 equiv.) or 2, 6-di-tert-butyl-4-methylphenol (BHT, 2.0 equiv.) as a radical scavenger to the reaction of 1a and NFSI completely suppressed the reaction. When BHT was used as a radical scavenger, the benzylic amination product 5 was obtained in 35% yield. These results suggest that the transformation involves radical intermediates. When the reaction was conducted in air, formation of 3a was completely inhibited, and α-amino ketone 6 was obtained in 68% yield. Information on the oxygen source was obtained by performing the reaction in an oxygen atmosphere using an ultra-dry solvent; only product 6 was obtained, in 73% yield. Only 3a was obtained when water was added to the reaction performed in a nitrogen atmosphere. When the reaction was performed in an oxygen atmosphere with 2 equiv. of H₂¹⁸O, no ¹⁸O-labeled α-amino ketone 6 was observed. These results indicate that the oxygen atom of 6 originated from molecular oxygen. On the basis of our experimental results and previous reports [53-58, 64, 65], we propose a plausible mechanism for this transformation (Scheme 4). Initially, interaction of Cu[(CH₃CN)₄PF₆], ligand L2, and NFSI gives copper(Ⅲ) species B, which leads to formation of a nitrogen-centered radical species C. Regioselective addition of C to the allylic alcohol provides benzylic radical D. Subsequent single-electron oxidation of D by a copper(Ⅱ) species regenerates the copper(Ⅰ) catalyst A, together with formation of a carbocation F. A semipinacol rearrangement of F delivers α-quaternary-β-amino ketone 3a as the final product.

Scheme 3. Mechanistic investigation.

Scheme 4. Plausible mechanism.

4 Conclusions

We have developed a novel copper-catalyzed radical amination/ 1, 2-carbon migration of allylic alcohols using a N-F reagent as an efficient amination source. The reaction leads to the formation of a variety of α-quaternary-β-amino ketones with various cyclic and open-chain structures, including spiro ketones. This transformation shows high efficiency, good substrate scope, and good functional group compatibility. Mechanistic studies suggest that the 1, 2-carbon migration reaction is induced by regioselective nitrogen-centered radical addition to the C=C bond. Further detailed mechanistic studies and synthetic applications using new types of amination source, as well as work on this transformation, are in progress in our laboratory.

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