Reactivity of some poly-1-alkynylsilicon and -tin compounds towards triallylborane—routes to novel heterocycles

Triallylborane reacts with most poly-1-alkynylsilanes (1–5), containing up to four CC units, or di(1-alkynyl)tin compounds (6) to give either siloles (8, 11, 14, 16), as the result of an intermolecular 1,1-allylboration followed by an intramolecular 1,1-vinylboration, or the novel 2-alkylidene-1,3-silaborolene (9) or 2-alkylidene1,3-stannaborolene derivatives (17), as the result of intermolecular 1,1-allylboration followed by an intramolecular 1,2-allylboration. In the case of the borolene derivatives, a second intramolecular 1,2-allylboration takes place to give 1,7-borasila- or 1,7-borastannabicyclo[4.3.0]nona-5,8-diene derivatives (10, 12, 13, 15, 18). If the starting materials are di(1-alkynyl)methylsilicon hydrides (2), the latter reaction affords selectively only one diastereomer (10(H)). All products were characterised by extensive multinuclear magnetic resonance spectra (1H-, 11B-, 13C-, 29Si-, and 119Sn-NMR).