Synthesis of symmetrical and unsymmetrical 2,5-bis(trialkylsilyl)furans and 2,6-bis(trialkylsilyl)-4H-pyrans from 1,4-and 1,5-bis(acylsilanes)

2,5-Bis(trialkylsilyl)furans and 3,6-bis(trialkylsilyl)-4H-pyrans have been synthesized by cyclodehydration of 1,4- and 1,5-bis(acylsilanes) under p-t oluenesulfonic acid catalysis. The 1,4-bis(acylsilanes) have been prepared from 1,2-bis(1,3-dithian-2-yl)ethane according to the reaction sequence met allation-silylation-dethioketalization. The 1,5-bis(acylsilanes) have been prepared from 1,3-bis(1,3-dithian-2-yl)propane by a similar strategy or fro m a S-N reaction of 1,3-dihalopropanes with 2-trialkylsilyl-2-lithio-1,3-di thiane and deprotection. The method allows efficient preparation of symmetr ical as well as unsymmetrical bis(silylated) heterocycles.