1-Boraadamantane: reactivity towards mono-1-alkynyltin, -germanium and -silicon compounds - synthesis of 4-methylene-3-borahomoadamantanes

The reaction of 1-boraadamantane 1 with 1-alkynyltin (3), -germanium (4), a nd -silicon compounds (5) leads to enlargement of the tricyclic system by f ormation of 4-methylene-3-borahomoadamantanes (6-9). These are 1,1-organobo ration reactions which proceed by cleavage of the M-C equivalent to bond (M = Sn, Ge, Si). There is evidence for 1,1-deorganoboration which apparently take place much more readily than for non-cyclic analogues, most likely as the result of the strained tricyclic system. When 2-ethyl-1-boraadamantane (2) is used, again 3-borahomoadamantanes are formed, the isomers 15-18. Th e product distribution is sensitive to steric effects. However, it appears that the B-C(H)Et bond in 2 is slightly more reactive than the B-CH2 bonds. All products were characterised by H-1-, B-11-,C-13-, Si-29- and Sn-119-NM R. (C) 2001 Elsevier Science B.V. All rights reserved.