C (Et)= CR [M= Si, R= Me: la, R= Ph: lb; M= Ge, R= Me: 2d, R= Ph: 2e] via the mono-and bisethyloboration compounds 3 or 4 (eg 3b, 4c) with different rates: Ge>> Si; Me> Ph. For comparison, compounds Sn (C= CR),[R= Me (F), R= Ph (G)] react with Et3B in the absence of a solvent to mixtures of various spirotin compounds (5f, 5g, 6f, 8f, 9g, log, llg) of which only 9g (R= Ph) corresponds to the spirosilanes and-germanes. This is the result of effective ...