title: Cyclizative radical carbonylations of azaenynes by TTMSS and hexanethiol leading to alpha-silyl- and thiomethylene lactams. Insights into the E/Z stereoselectivities.
abstract: Free-radical mediated cyclizative carbonylations of azaenynes were carried out using TTMSS as a radical mediator to compare the efficiency and the stereochemistry with those using tributyltin hydride. Using a substrate concentration of 0.1 M, the reactions gave good yields of alpha-silylmethylene lactams having four to seven-membered rings. The observed E-diastereoselectivity of the resulting vinylsilane moiety is in sharp contrast to the Z-selectivity observed during the analogous carbonylation using tributyltin hydride. When hexanethiol was used as the radical mediator, alpha-thiomethylene lactams were formed with E-favoring stereoselectivity again. Ab initio and DFT molecular orbital calculations on the stability of E and Z products were carried out for a set of five-membered methylene lactams bearing SnH3, SiH3, and SMe groups. The distinct thermodynamic preference for the Z-isomer was only predicted for the Sn-bearing lactam. A steric effect due to the bulky (TMS)3Si group is proposed for the E-selectivity observed in the TTMSS-mediated reaction.
authors.affiliation: Department of Chemistry, Faculty of Arts and Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
authors.forename: Mami
authors.initials: M
authors.lastname: Tojino
authors.forename: Noboru
authors.initials: N
authors.lastname: Otsuka
authors.forename: Takahide
authors.initials: T
authors.lastname: Fukuyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsubara
authors.forename: Carl H
authors.initials: CH
authors.lastname: Schiesser
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kuriyama
authors.forename: Hironari
authors.initials: H
authors.lastname: Miyazato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Minakata
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Komatsu
authors.forename: Ilhyong
authors.initials: I
authors.lastname: Ryu