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

Mami Tojino, Noboru Otsuka, Takahide Fukuyama, Hiroshi Matsubara, Carl H. Schiesser, Hiroki Kuriyama, Hironari Miyazato, Satoshi Minakata, Mitsuo Komatsu, Ilhyong Ryu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

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.

Original languageEnglish
Pages (from-to)4262-4267
Number of pages6
JournalOrganic and Biomolecular Chemistry
Volume1
Issue number23
DOIs
StatePublished - 7 Dec 2003

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