Base catalyzed rearrangement of pi-conjugated sulfur and selenium bridged propargylic systems

A series of novel pi -conjugated bis-propargylic sulfides, selenides, sulfo xides and sulfones have been prepared. In the presence of amine bases these compounds underwent facile isomerization to the corresponding allenes, fol lowed by a tandem cyclization and aromatization of the latter via a diradic al intermediate. While the reactions of sulfones and sulfoxides were almost spontaneous and proceeded in practically quantitative yield, the sulfides and selenides exhibited modest reactivity and required more polar solvents to afford the corresponding thiophenes and selenophenes. Some mechanistic s tudies and DNA cleaving properties are also presented. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.