Organopotassium‐Catalyzed Silylation of Benzylic C(sp³)−H Bonds

Abstract

Benzylsilanes have found increasing applications in organic synthesis as bench-stable synthetic intermediates, yet are mostly produced by stoichiometric procedures. Catalytic alternatives based on the atomeconomical silylation of benzylic C(sp 3 )À H bonds remain scarcely available as specialized directing groups and catalytic systems are needed to outcompete the kinetically-favored silylation of C(sp 2 )À H bonds. Herein, we describe the first general and catalytic-in-metal undirected silylation of benzylic C(sp 3 )À H bonds under ambient, transition metal-free conditions using stable tert-butyl-substituted silyldiazenes (tBuÀ N=NÀ SiR 3 ) as silicon source. The high activity and selectivity of the catalytic system, exemplified by the preparation of various mono-or gem-bis benzyl(di)silanes, originates from the facile generation of organopotassium reagents, including tert-butylpotassium.

Silylation of Allylic C(sp3)–H Bonds Enabled by the Catalytic Generation of Allylpotassium Complexes

“…27 Finally, we investigated the mechanism of the reaction. In accordance with our previous study, 17 we postulated that facile metalation of allylic C(sp 3 )−H bonds should readily take place upon anionic decomposition of the silylated diazene. To this end, we first demonstrated that allyl potassium intermediates are generated during the silylation of two representative substrates, namely, allylbenzene 3 and allylamine 25.…”

“…In line with these observations and our previous computational results on the silylation of benzylic C(sp 3 )−H bonds, 17 we propose the general catalytic cycle presented in Scheme 6C, which begins with an initiation step between tBuOK and 1a (not shown) that affords the π-allyl potassium species A. The latter then rapidly undergoes K/Si transmetalation with diazene 1a to give the potassium diazenyl complex B bound to the linear allylsilane moiety via a cation−π interaction.…”

“…Toward this goal, we have recently reported that potent metalating agents can be generated catalytically when tert -butyl-substituted silyldiazenes ( t Bu–NN–SiR 3 ) are treated with a catalytic amount of a potassium salt (typically t BuOK). This process has been fruitfully exploited in the catalytic silylation of unactivated C­(sp 2 )–H 16 and benzylic C­(sp 3 ) –H bonds . We herein disclose a novel and operationally simple approach toward linear allylsilanes that capitalizes on the facile catalytic generation of nucleophilic allylpotassium species directly from 1- or 2-alkenes (Scheme C) …”

“…This process has been fruitfully exploited in the catalytic silylation of unactivated C(sp 2 )−H 16 and benzylic C(sp 3 )−H bonds. 17 We herein disclose a novel and operationally simple approach toward linear allylsilanes that capitalizes on the facile catalytic generation of nucleophilic allylpotassium species directly from 1-or 2-alkenes (Scheme 1C). 18 Using triethylsilyl-substituted diazene 1a as a silicon source, we started our study with the silylation of trans-βmethylstyrene 2 as a model internal 2-alkene (Table 1 and Table S1 in the SI) that displays an allylic methyl group.…”

Fluoride-Catalyzed Arylation of α-(Trifluoromethyl)styrene Derivatives with Silicon-Masked, Functionalized Aryl Pronucleophiles

“…Recently rediscovered and synthetically versatile N -aryl- N′ -silyldiazenes begin to find useful applications as latent aryl pronucleophiles. − Anionic Lewis bases mediate their desilylation, generating aryl-substituted diazenyl anions that eventually collapse into dinitrogen and aryl nucleophiles that can be decorated with a broad spectrum of functional groups. Accordingly, we have been seeking new reactions for these silicon-masked aryl pronucleophiles.…”