Free-Radical-Promoted Site-Selective C–H Silylation of Arenes by Using Hydrosilanes

Abstract

A free-radical-promoted aryl/heteroaryl C-H silylation using hydrosilane was developed. This cross-dehydrogenative silylation enables both electron-rich and electron-poor aromatics to afford the desired arylsilanes in unique selectivity. A "para-selectivity" was observed by examination of over 54 examples. This exceptional orientation is quite different from that in Friedel-Crafts C-H silylation or transition-metal-catalyzed dehydrogenative silylation.

A para‐C–H Functionalization of Aniline Derivatives via In situ Generated Bulky Hypervalent Iodinium Reagents

“…Aromatic carboxylic anilides require a longer reaction time. N ‐Phenyl‐benzamide[16i] and N ‐phenylpicolinamide[16k] which have been studied previously, afforded the corresponding products ( 19–20 ), and a previously reported substrate, N ‐(naphthalen‐1‐yl)picolinamide was also compatible with these reaction conditions, delivering 21 in a satisfactory yield. In addition to carboxylic anilides, N ‐Boc aniline and N ‐sulfonylaniline also gave novel bromination products ( 22–23 ).…”

“…In addition to carboxylic anilides, N ‐Boc aniline and N ‐sulfonylaniline also gave novel bromination products ( 22–23 ). [16i] We continued to explore the versatility of this protocol, examining the para ‐bromination of synthetically useful secondary anilides. As shown in Scheme C, a variety of building blocks related to pharmaceutical compounds, such as indoline‐2,3‐dione, dihydroquinolinone and phenanthridin‐6( 5H )‐one, underwent this para ‐selective reaction smoothly, delivering the corresponding para ‐bromo anilides ( 24–27 ) in moderate to good yields.…”

“…However, owing to the lack of an ortho sterically hindering group, control of the regioselectivity for para ‐functionalization of common aniline derivatives is difficult, and only a few examples have been reported. [12d], Consequently, a general protocol to install various para ‐substituents on anilides remains highly desirable. Recently, a ruthenium‐catalyzed σ‐activation strategy has been applied to para ‐selective alkylation and difluoromethylation of aniline derivatives by Frost's group and Zhao and Lan et al Despite these progresses and works on C5‐functionalization of 8‐acylamino quinolines, a general transition‐metal‐free para ‐functionalization of aniline derivatives with reduced toxicity has scarcely been reported.…”

Transition‐Metal‐Free Direct C−H Silylation of Electron‐Deficient Heteroarenes with Hydrosilanes via a Radical Mechanism

“…Alternatively, free‐radical‐promoted direct C−H silylations of (hetero)arenes have also attracted attention in this field . Liu and co‐workers have reported the direct C−H silylation of various (hetero)arenes via a radical mechanism, which enabled the introduction of silyl groups at the meta ‐position of 2‐substituted pyridines (Scheme c) . Meanwhile, to the best of our knowledge, the ortho ‐selective direct C−H silylation of pyridines with hydrosilanes has not yet been reported.…”

“…Ethyl‐3‐methylisonicotinate ( 1 g ) provided a regioisomer mixture of the corresponding 2‐mono‐ and 6‐monosilylated products ( 2 g and 3 g ). Interestingly, our approach allowed the insertion of silyl groups at the ortho ‐position of 2‐phenylpyridine ( 1 h ), preferentially . The reaction of methyl nicotinate ( 1 i ) afforded 2‐monosilylated pyridine 2 i and a regioisomer mixture of disilylated pyridines 3 i and 3 i’ .…”