Generation and solution-phase behaviour of some 2-halogeno-1,3-ring-fused cyclopropenes

Abstract

The title cyclopropenes 2b are readily formed by reaction of ring-fused β-silylated-gemdihalogenocyclopropanes of the general type 1b with tetrabutylammonium fluoride in tetrahydrofuran solution. Those halogenocyclopropenes 2b which are fused to a seven- or eight-membered ring can be trapped with a range of 1,3-dienes and the corresponding Diels-Alder adducts 3b are produced in high yield. In contrast, those chlorocyclopropenes which are fused to a five- or six-membered ring cannot be trapped efficiently by added diene because they each undergo rapid rearrangement to an isomeric vinyl carbene. Thus, 6-chlorobicyclo[3.1.0]hex-1 (6)-ene 27 undergoes ring-expansion to carbene 28 which either in..