Clusters N2B4R6 from the fusion of rings NB2R3: mechanism
摘要:
Whereas the fusion of three-membered rings NB2R2R' (1b-d; R = Bu-t R' = Me, Et, iPr) gives diaza-nido-hexaboranes N2B4R4R2' (2b-d), the fusion of the corresponding 1e (R' = CH2 Bu-t) yields the isomeric tetracyclic molecule 3e, which crystallizes in the space group P1. Two B = N double bonds in 3 correspond to four B-N single bonds in 2 and thus indicate a transformation of 3 into 2 via an antarafacial (2 + 2) cycloaddition. The isolation of 3e offers a mechanistic understanding of the fusion of 1 to give 2 via 3, including the observed stereospecificity. (C) 1998 Elsevier Science S.A.