Labelling studies of the formation of cyclopentadienes from the reaction of 1,1-dibromo-2-vinylcyclopropanes with methyl lithium

Labelling studies of the conversion of (5, R1 = R2= Me) to (9) on reaction with methyl lithium are consistent with an intermediate (4, R1= R2 = Me) or a carbenoid with no plane of symmetry through the ring, in which selective migration of Ha (Hb and Hd in (1, R1= R2 = Me)) occurs.