1,1‐Organoboration of Di‐1‐alkynylsilanes with Alkynyl Groups of Different Reactivity: New Organometallic‐Substituted Siloles

The synthesis of alkynyl[(trimethylstannyl)ethynyl]dimethylsilanes 4 [alkynyl R1—C≡C: R1 = Bu (b), tBu (c), iPent (d), Ph (e), SiMe3 (f)] is reported. The intermolecular 1,1‐ethyloboration of 4 with triethylborane 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‐(trimethylstannyl)siloles 7. Protodeborylation of 7 with water gives the 2‐(trimethylstannyl)siloles 8, and protodeborylation and protodestannylation with an excess of acetylacetone affords the siloles 9. Multinuclear NMR (1H‐, 11B‐, 13C‐, 29Si‐, and 119Sn‐) serves for monitoring the reactions and for the characterization of the products.