Reactivity of mono-1-alkynyltin and -germanium compounds towards triallylborane

Triallylborane, All(3)B (4), reacts with trialkyl(1-alkynyl)tin compounds 1 R3Sn-C drop CR1 [R = Me, R-1 = Me (a), Bu-t (b), Ph (c), SiMe3 (d), SnMe3 (e)] and 2 (R = Bu, R-1 = ferrocenyl) and also with 1-phenylethynyl(trimethyl)germanium (3c) preferably by 1,1-allylboration to give the organometallic-substituted alkenes 6, 8 and 10. In the cases of 1b and 1d, allyl/alkynyl exchange takes place instead. However, the formation of the alkene 6e was observed at - 30 degrees C. In the case of Ic, 1,2-allylboration, leading to the alkene 7c, competes with 1,1-allylboration, the ratio 6c/7c being dependent on the polarity of the respective solvent (more of 6e in a more polar solvent). All(3)B proved to be much more reactive than triethylborane, Et3B (5). All products were characterised by H-1, B-11,C-13 and Sn-119 NMR. (C) 2000 Elsevier Science S.A. All rights reserved.