Lewis Acid Catalyzed Stereoselective Carbosilylation. Intramolecular trans-Vinylsilylation and trans-Arylsilylation of Unactivated Alkynes
journal contributionposted on 10.10.2001, 00:00 by Naoki Asao, Tomohiro Shimada, Takashi Shimada, Yoshinori Yamamoto
Intramolecular trans-vinylsilylation using silicon-tethered alkynylvinylsilanes 3b−c was catalyzed dramatically by Lewis acids such as EtAlCl2 to give the corresponding six-membered silacycles 4b−c in high yields. The reaction proceeded via an exo-mode cyclization. In addition to the vinylsilylation, the intramolecular trans-arylsilylations using carbon-tethered alkynylarylsilanes 8a−b were also catalyzed by Lewis acids such as HfCl4 to give six- and seven-membered cyclic (E)-vinylsilanes 9a−b, respectively. The cyclization of silicon-tethered substrates 13a−d afforded five- and six-membered silacycle products 14a−d in low to high yields. All arylsilylation reactions proceeded via an exo-mode fashion exclusively.