Silicon-carbon unsaturated compounds .60. Reactions of lithium silenolates with dienes

The chemical properties of lithium silenolates toward dienes were studied. The reaction of lithium 2-tert-butyl-1,1-bis(trimethylsilyl)silen-2-olate (1a) with butadiene at -40 degrees C, followed by hydrolysis, afforded 2-tert-butyl-1,1-bis(trimethylsilyl)silacyclohex-4-en-2-ol derived from [2 + 4] cycloaddition of 1a with butadiene, in 94% yield. Similar treatment of lithium 2-adamantyl-1,1-bis(trimethylsilyl)silen-2-olate (1b) gave the respective adduct in 87% yield. The reactions of lithium silenolates 1a,b with 2,3-dimethylbutadiene, isoprene, and 1,3-pentadiene proceeded in a fashion similar to those with butadiene to give the [2 + 4] cycloadducts in high yields. The reactions of 1a,b with 2,3-dimethylbutadiene and butadiene at room temperature gave the products originated from 1,1-bis(trimethylsilyl)silacyclohexa-1,4-diene intermediates. The crystal structure of 10-adamantyl-2,3,6,7-tetramethyl-9-(trimethylsilyl)-9- silabicyclo[4.4.0]deca-2,6-diene (6b), which was obtained from the reaction of 1b with 2,3-dimethylbutadiene at room temperature, was determined by a single-crystal X-ray diffraction study.