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|Title:||Synthetically Useful Dipole-Stabilized Carbanions From Thioesters and Thiocarbamates|
|Author(s):||Becker, Peter Donald|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||In an investigation of the formation of dipole-stabilized carbanions from thioesters, deprotonation of a tertiary center at the carbon adjacent to the sulfur of a thioester was found for the first time. Isopropyl, 2-octyl, and 4-tert-butylcyclohexyl 2,4,6-triisopropylthiobenzoates react with sec-butyllithium/TMEDA at -98(DEGREES)C to give synthetically useful (alpha)-lithio thioesters. These species react with electrophiles including primary alkyl halides and a variety of carbonyl compounds to give substituted thioesters. Study of the optically active 2-octyl thioester as well as the cis-4-tert-butylcyclohexyl thioester has shown that (alpha)-lithio thioesters are not configurationally stable. A general synthesis of trisubstituted thiiranes is provided by the action of sodium hydride on (beta)-hydroxy thioesters, which are obtained by reaction of the (alpha)-lithio thioesters with aldehydes.
Heptyl, neopentyl, diethylaminoethyl, methoxymethyl and allyl 2,4,6-triisopropylthiobenzoates form stable anions on reaction with sec-butyllithium/TMEDA which can be trapped with electrophiles. Ethoxyethyl and 2-methoxymethyl 2,4,6-triisopropylthiobenzoates undergo elimination to form vinyl thioesters which in turn are deprotonated adjacent to sulfur and react with electrophiles. The n-butoxymethyl 2,4,6-triisopropylthiobenzoate on the other hand decomposes to give lithium 2,4,6-triisopropylthiobenzoate.
The deprotonation of primary alkyl thiocarbamates adjacent to sulfur is also reported for the first time. Reaction of sec-butyllithium/TMEDA with S-ethyl and S-heptyl N,N-dimethylthiocarbamates gives the (alpha)-lithio species which react with electrophiles to give substituted thiocarbamates. These species are more readily hydrolyzed than the thioesters so they provide ready access to (alpha)-lithioalkylthiol synthons.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
|Date Available in IDEALS:||2014-12-15|