Md. Bachi et al., THIOL-MEDIATED FREE-RADICAL CYCLIZATION OF ALKENYL AND ALKYNYL ISOCYANIDES, Journal of organic chemistry, 59(25), 1994, pp. 7752-7758
Thiol-mediated free radical cyclizations of but-3-enyl and but-3-ynyl
isocyanides of types 6-8 give new access to 3,5-disubstituted 2-(alkyl
- and 2-(arylthio)pyrrolines 11, 12, and 18. When 2-mercaptoethanol is
used with the same isocyanides the reaction results in pyroglutamates
16, 17, or 19. These cyclizations involve the formation of a new carb
on-carbon bond through intramolecular addition of a carbon-centered th
ioimidoyl radical to a carbon-carbon multiple bond. Although cyclic pr
oducts are usually obtained in high yields, in a few cases a competing
radical degradation process leading to isothiocyanates was observed.
Isocyanide 8a carrying an allyl(phenyl) sulfide moiety isomerizes to 2
-(phenylthio)pyrroline 24 in a series of sequential steps.