Studies in Sigmatropic Rearrangement: Synthesis of a [6,6]Pyranothiopyran Ring System by Sequential Claisen Rearrangement and Pyridine Hydrotribromide Mediated Regioselective “6-Endo” Cyclization

Abstract

[reaction: see text] 4-(4'-Aryloxybut-2'-ynylthio)[1]benzopyran-2-ones are refluxed in chlorobenzene to afford 4-aryloxymethylthiopyrano[3,2-c][1]benzopyran-5(2H)-ones which are subsequently subjected to heating in o-dichlorobenzene in the presence of N,N-diethylaniline and then treated with pyridine hydrotribromide to give [6,6]pyranothiopyrans in almost quantitative yield.