1,1-ORGANOBORATION OF DI-1-ALKYNYLSILANES WITH ALKYNYL GROUPS OF DIFFERENT REACTIVITY - NEW ORGANOMETALLIC-SUBSTITUTED SILOLES

The synthesis of alkynyl[(trimethylstannyl)ethyl]dimethylsilanes 4 [al kynyl R1-C=C: R1 = Bu (b), tBu (c), iPent (d), Ph (e), SiMe3 (f)] is r eported. The intermolecular 1,1-ethyloboration of 4 with triethylboran e takes place selectively at the Sn-C= bond to give first the alkenyl( alkynyl)dimethylsilanes 5 and 6. There exists an equilibrium between 5 and 6, and compound 6 has the suitable stereochemistry for the final intramolecular 1,1-vinyloboration to form the 4-(diethylboryl)-2-(trim ethylstannyl)siloles 7. Protodeborylation of 7 with water gives the 2- (trimethylstannyl)siloles 8, and protodeborylation and protodestannyla tion with an excess of acetylacetone affords the siloles 9. Multinucle ar NMR (H-1-, B-11-, C-13-, Si-29-, and Sn-119-) serves for monitoring the reactions and for the characterization of the products.