Studies in sigmatropic rearrangement: synthesis of a [6,6]pyranothiopyran ring system by sequential claisen rearrangement and pyridine hydrotribromide mediated regioselective "6-Endo" cyclization.
[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.
Majumdar
K C
KC
Department of Chemistry, University of Kalyani, West Bengal, India. kcm@klyuniv.ernet.in
Kundu
U K
UK
Ghosh
S K
SK