Silylene reactions with 1,7-octadiene-3,5-diynes: evidence for the intermediate formation of a bis(silaethene)

Treatment of 1,4-bis(cyclohexen-1-yl)buta-1,3-diyne with di-tert-butylsilylene (1) furnishes the acetylene-linked bis(2-silacyclobutene) derivative 9, presumably via a two-fold [2+2] cycloaddition reaction of the bis(silaethene) intermediate to the endocyclic double bonds of the cyclohexene rings. However, a similar reaction of 1 with the sterically more encumbered 1,7-octadiene-3,5-diyne 10 yields the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene 12, formed by rearrangement of the two-fold [1+2] cycloaddition product of 1 to the C/C triple bonds of 10. The structures of 9 and 12 have been determined by X-ray crystallography.