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 ( 1 H-, 11 B-, 13 C-, 29 Si-, and 119 Sn-NMR).