TBAI-assisted direct C-H activation of indoles with β- E -styrene sulfonyl hydrazides: a stereoselective access to 3-styryl thioindoles.

The current work describes the challenging introduction of a vinyl sulfide group by simple C-H activation on a variety of substrates. The direct C-H activation of indoles with β-( E )-styrene sulfonyl hydrazides under the sulfenylation conditions, assisted by the iodic catalyst tert -butyl ammonium iodide (TBAI), afforded a series of ( E )-styrylthioindoles. Accordingly, β-( E )-styrene sulfonyl hydrazides undergo radical cross-coupling reactions with a variety of substituted indoles to afford structurally diverse indole vinyl thioethers in moderate to high yields with E -stereoselectivity. This method is metal-catalyst-free and is valuable not only because of its novelty, but also for providing a convenient synthetic pathway to a variety of ( E )-styrylthioindoles with retention of the configuration. The current study paves the way for the use of β-( E )-styrene sulfonyl hydrazides as a unique styryl mercaptan source in chemical synthesis.