Pyrrolo[2,1-b]thiazole Derivatives by Asymmetric 1,3-Dipolar Reactions of Thiazolium Azomethine Ylides to Activated Vinyl Sulfoxides

1,3-Dipolar reactions of thiazolium azomethine ylides to enantiopure cyclic and acyclic vinyl sulfoxides provide an efficient access to polyfunctionalized pyrrolo[2,1-b][1,3]thiazoles in a highly regio- and stereoselective manner. Regioselectivity can be inverted by modifying the position of the sulfinyl group at the double bond of the sulfinylfuranones. The sulfoxide is the main controller of the endo selectivity of these processes as well as of the π-facial selectivity in reactions of (Z)-3-p-tolylsulfinylacrylonitriles. In contrast, the π-facial selectivity in reactions of 5-alkoxy-3-p-tolylsulfinyl furan-2(5H)-ones is mainly controlled by the configuration at C-5, affording the anti adducts with respect to the alkoxy group as the major or exclusive adducts.