AN UNUSUAL EXAMPLE OF STEREOELECTRONIC CONTROL IN THE RING-OPENING OF 3,3-DISUBSTITUTED 1,2-DICHLOROCYCLOPROPENES

Quantitative SCF-MO calculations at the PM3 and ab initio level reveal that the origin of the stereoselective ring opening of 1,2-dichloro-3,3-disubstituted cyclopropenes (1, R2 = CH2Cl, CH2OMe or CH2Ph) to give vinylcarbenes 2 via transition state 5 arises from stereoelectronic control, in contrast to that of cyclopropenes having bulky non-polar substituents such as R2 = Pr(i) which favours a less hindered transition state 6.