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Lewis Acid/Hexafluoroisopropanol Lewis Acid/Hexafluoroisopropanol: A Promoter System for Selective ortho-C-Alkylation of Anilines with Deactivated Styrene Derivatives and Unactivated Alkenes Shengdong Wang, Guillaume Force, Régis Guillot, Jean-François Carpentier, Yann Sarazin, Christophe Bour, Vincent Gandon, David Lebœuf To cite this version: Shengdong Wang, Guillaume Force, Régis Guillot, Jean-François Carpentier, Yann Sarazin, et al.. Lewis Acid/Hexafluoroisopropanol: A Promoter System for Selective ortho-C-Alkylation of Anilines with Deactivated Styrene Derivatives and Unactivated Alkenes. ACS Catalysis, American Chemical Society, 2020, 10 (18), pp.10794-10802. 10.1021/acscatal.0c02959. hal-02961178 HAL Id: hal-02961178 https://hal-univ-rennes1.archives-ouvertes.fr/hal-02961178 Submitted on 8 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Page 1 of 10 ACS Catalysis 1 2 3 4 5 6 7 Lewis Acid/Hexafluoroisopropanol: A Promoter System for Selective 8 ortho-C-Alkylation of Anilines with Deactivated Styrene Derivatives 9 10 and Unactivated Alkenes 11 a a a b b 12 Shengdong Wang, Guillaume Force, Régis Guillot, Jean-François Carpentier, Yann Sarazin, 13 Christophe Bour,a Vincent Gandon*,a,c and David Lebœuf*,d 14 15 a Institut de Chimie Moléculaire et des Matériaux d’Orsay (ICMMO), CNRS UMR 8182, Université Paris-Saclay, Bâtiment 16 420, 91405 Orsay, France. 17 b Univ. Rennes, CNRS UMR 6226, Institut des Sciences Chimiques de Rennes (ISCR), 35000 Rennes, France. 18 c.Laboratoire de Chimie Moléculaire (LCM), CNRS UMR 9168, Ecole Polytechnique, Institut Polytechnique de Paris, route de Saclay, 91128 Palaiseau cedex, France. 19 d 20 Institut de Science et d’Ingénierie Supramoléculaires (ISIS), CNRS UMR 7006, Université de Strasbourg, 8 allée Gaspard 21 Monge, 67000 Strasbourg, France. 22 KEYWORDS alkenes, anilines, hexafluoroisopropanol, Lewis acid, ortho-C-alkylation 23 ABSTRACT: Aniline derivatives are frequently encountered in molecules of industrial relevance such as dyes or antioxidants, 24 which make the development of synthetic methods for the functionalization of these privileged structures highly sought-after. 25 A general protocol for the hydroarylation of electronically diverse alkenes with anilines would be ideal to provide densely 26 functionalized compounds. Yet, this transformation has been underexplored compared to more traditional hydroarylation of 27 unactivated alkenes because of the significant challenges associated with the control of the selectivity and its substrate 28 tolerance. Herein, we describe a selective, versatile and user-friendly ortho-C-alkylation of anilines with alkenes that hinges 29 on the beneficial combination of a Lewis acid (Ca(II)) and hexafluoroisopropanol as a solvent. This protocol allows for the 30 extension of this transformation to highly deactivated styrenes and demonstrates a remarkable improved reactivity regarding 31 aliphatic alkenes, styrene derivatives and dienes. In addition, DFT computations were performed which, combined with 32 experimental observations, suggest a nearly concerted mechanism that impart the ortho-selectivity. 33 34 35 Diarylamines, and generally simple anilines, are prevalent compounds prepared through non-covalent interactions (- 36 building blocks in organic synthesis. They offer a wide anion, lone pair- or - interactions).9 In the realm of 37 variety of applications, including pharmaceuticals, hydroarylation of unactivated alkenes, a traditional agrochemicals, and functional organic materials.1 Besides, 38 approach involves the use of a Lewis or Brønsted acid, they can be rapidly converted into acridinium derivatives,2 which typically triggers the formation of a stabilized 39 which have emerged as powerful catalysts for photoredox carbocation species and a subsequent trapping by 40 transformations.3 Within this context, the identification of (hetero)arene nucleophiles.4 Yet, this strategy often leads to 41 synthetic methods to increase the molecular complexity both ortho- and para-products, limiting its applicability. The 42 and diversity of these compounds has been thoroughly problem becomes even more pronounced in the case of 43 investigated over the last decades. Among them, the anilines, which can also undergo hydroamination reactions 44 hydroarylation of unactivated alkenes with anilines (Schemes 1a-1c).10 To account for the formation of the 45 represents arguably an ideal process: an atom- and step- ortho-alkylated product, Beller and coworkers alluded to a 46 economic transformation featuring feedstock alkenes and concerted mechanism that would differ from that of a 47 anilines to form key CC bonds in an efficient manner.4 typical proton-catalyzed hydroarylation (Scheme 1c).6a 48 Despite many studies outlined in Scheme 1,5-7 the intrinsic However, in the case of Lewis and Brønsted acid-based 49 limitations associated with this transformation have still to strategies, the transformation led to uneven selectivities 50 be addressed, including its unpredictable selectivity (ortho- between ortho-C alkylation and hydroamination depending 6a,6c-6l,6n 51 C alkylation/para-C alkylation/hydroamination), its on the promoter system used (from 1:0 to 0:1), incompatibility with highly deactivated styrenes and N- suggesting competing reaction pathways. To date, the 52 (alkyl or aryl) diarylamines and its limited reactivity iridium-catalyzed enantioselective ortho-alkylation of 53 regardingAccepted aliphatic alkenes. In particular, the dearth of Manuscriptacetanilides described by the group of Bower can be 54 reports regarding highly deactivated styrenes8 that considered as a reference in terms of selectivity (Scheme 55 incorporate strong electron-withdrawing groups is 1f);6o,6t yet, no highly deactivated styrene was investigated, 56 detrimental to discovering new applications, as such a specific directing-group was required, and tertiary 57 substrates may impart original properties to the anilines were incompatible with the reaction conditions. In 58 59 60 ACS Paragon Plus Environment ACS Catalysis Page 2 of 10 Scheme 1. Hydroarylation and hydroamination of olefins with aniline derivatives. 1 2 I: Lewis and Brønsted Acid Strategies II: Transition-Metal Strategies a) Stephan (ref. 6n): [(C6F5)3PF][B(C6F5)4] d) Hartwig (ref. 11c) 3 H Ph H Ph N N [Pd] CN 4 NH2 5 Ph + [Pd] HN 6 Ph CN R [P] H C NH2 7 H17C8 17 8 e) Bertrand (ref. 6m) 8 b) Bergman (ref. 6f): PhNH3B(C6F5)4·Et2O R1 R2 N N 9 N [Au] R-NH2 R1 [Au] 10 N mixture R1 + R + N Ph Ph H of isomers 11 observed R R 12 (o/N) Ph + Bower c) Beller (ref. 6a): HBF4 f) (ref. 6o and ref. 6t) if R2 = H 13 NHAc 1 14 R R1 Ac N H N H N Ph + [Ir] [Ir] H 15 H H * R DG Ph 16 R Ph NHAc critical for the reaction only example of 17 moderate electrophilicity of anilinium (no reaction with NMeAc) enantioselective version 18 III: Radical Strategies IV: This Work Envisioned catalytic cycle with the promoter system: [Ca], HFIP 19 g) Patureau (ref. 6u) 20 R1 S R2 H S N O 2 21 [Ca] S H N 1 Ph [Ag] O CF3 CF3 R 22 + NH N N H H n Ph CF3 CF3 2 23 N2 Ph 3 R (HFIP)n R 3 24 plausible mechanism R [Ca(OCH(CF3)2)] 25 h) Zhang (ref. 12) X 3 1 Ph H * Ph R R 26 N Ph 1 N Ph N R H n+1 Ph 2 2 27 Ph N Cu N N R 3 R Ph + [Cu] n R Cu Ln Ln H 28 Blue LED 40 W Ph CF3 Ph R3 H high ortho-selectivity Ph O 29 O CF3 highly deactivated styrenes [Ca] 30 CF3 CF3 aliphatic alkenes Current limitations of strategies I-III: n dienes 31 - precise control of the selectivity - no reactions for highly deactivated styrenes key: harnessing electrophilicity of N-alkyldiarylamines 32 - no reactions for tertiary diarylamines - scarce examples for aliphatic alkenes and dienes anilinium to favor ortho-C-alkylation 33 Manuscript 34 35 contrast, transition-metal-catalyzed reactions are more dienes and styrene derivatives, which typically generate 36 prone to produce hydroamination adducts11 or give rise to oligomers in HFIP,16 could be tolerated. Herein, we disclose 37 para-selectivity in the absence of directing groups our findings regarding this transformation with a special 38 (Schemes 1d-1e).6m,6q Visible-light photoredox protocols emphasis on highly deactivated styrenes and their synthetic 39 are curbed with similar limitations (Schemes 1g-1h).12 applications. This approach provides an amenable and 40 broadly applicable method to break the stalemate on the Our recent studies demonstrated that the use of HFIP as a selective ortho-C-alkylation of anilines. The mechanistic 41 solvent13 paired with a Lewis or Brønsted acid enables the considerations are further supported by DFT computations. 42 activation of highly unreactive olefins.8f,14 Conceptually, the Moreover, this study shows how the nature of the 43 role of the catalyst in these examples is not to directly substrates can dictate the ortho/para selectivity.17 44 activate the nucleophile or the electrophile, but, instead, to 45 augment the acidity of a H-bond network of HFIP At the outset, we examined the feasibility of this concept by 46 molecules.8f,14a In search of a reliable and selective ortho-C- investigating the inherent reactivity of highly deactivated 4- 47 alkylation of anilines with olefins and inspired by the work cyanostyrene 1a with diphenylamine 2a6u (4 equiv.) in the 48 of Beller, we reasoned that, under highly acidic conditions, presence of the promoter system that we previously 49 anilines would provide an anilinium cation, which could described for hydrofunctionalizations: Ca(NTf2)2/nBu4NPF6 18 50 react through a 6-membered transition state to generate the (20 mol%) in HFIP (0.2M) (Table 1).
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