Stereochemistry of Disilanylene-containing Cyclic Compounds – Synthesis and Palladium-catalyzed Reactions of cis- and trans-3,4- Benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene

Abstract

The synthesis and palladium-catalyzed reactions of cis- and trans-3,4-benzo-1,2-diisopropyl- 1,2-dimethyl-1,2-disilacyclobut-3-ene (1a and 1b) are reported. Their reactions with diphenylacetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) proceeded with high stereospecificity to give cis- and trans-5,6-benzo-1,4-diisopropyl-1,4-dimethyl- 2,3-diphenyl-1,4-disilacyclohexa-2,5-diene, 2a and 2b, in 95% and 93% yield, respectively. Similar palladium-catalyzed reactions of 1a and 1b with monosubstituted acetylenes, such as 1-hexyne, tert-butylacetylene, phenylacetylene, and trimethylsilylacetylene, also proceeded stereospecifically to afford the respective cis- and trans-5,6-benzo-1,4-disilacyclohexa-2,5-dienes, 3a - 6a and 3b - 6b, in excellent yields and as the sole products. The palladium-catalyzed reaction of 1a with styrene gave a mixture consisting of two stereoisomers, cis-2- and trans-2-phenyl-substituted 5,6- benzo-(r-1),cis-4-diisopropyl-1,4-disilacyclohex-5-ene 7a and 8a in a ratio of 5 : 3 in 72% combined yield, while the reaction of styrene with 1b afforded two stereoisomers, 7b and 8b, in a ratio of 2 : 1 in 80% combined yield. With 1-hexene, 1a gave two stereoisomers, 5,6-benzo-cis-2-(nbutyl)-( r-1),cis-4-diisopropyl- and 5,6-benzo-trans-2-(n-butyl)-(r-1),cis-4-diisopropyl-1,4-dimethyl- 1,4-disilacyclohex-5-ene, 9a and 10a, in a ratio of 1 : 1 in 70% combined yield. A similar reaction of 1b with 1-hexene produced 5,6-benzo-cis-2-(n-butyl)-(r-1),trans-4-diisopropyl-1,4-dimethyl-1,4- disilacyclohex-5-ene in 81% yield and as a single isomer