Issue 23, 2003

Cyclizative radical carbonylations of azaenynes by TTMSS and hexanethiol leading to α-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 α-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, α-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.

Graphical abstract: Cyclizative radical carbonylations of azaenynes by TTMSS and hexanethiol leading to α-silyl- and thiomethylene lactams. Insights into the E/Z stereoselectivities

Supplementary files

Article information

Article type
Paper
Submitted
07 Aug 2003
Accepted
17 Sep 2003
First published
21 Oct 2003

Org. Biomol. Chem., 2003,1, 4262-4267

Cyclizative radical carbonylations of azaenynes by TTMSS and hexanethiol leading to α-silyl- and thiomethylene lactams. Insights into the E/Z stereoselectivities

M. Tojino, N. Otsuka, T. Fukuyama, H. Matsubara, C. H. Schiesser, H. Kuriyama, H. Miyazato, S. Minakata, M. Komatsu and I. Ryu, Org. Biomol. Chem., 2003, 1, 4262 DOI: 10.1039/B309944J

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