Stereochemistry of Disilanylene-Containing Cyclic Compounds. Thermal Reactions of <i>cis</i>- and <i>trans</i>-3,4-Benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene

The thermal reaction of <i>cis</i>-3,4-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene (<b>1a</b>) with <i>tert</i>-butyl alcohol at 300 °C for 24 h proceeded with high stereospecificity to give <i>erythro</i>-1-(<i>tert</i>-butoxyisopropyl­methylsilyl)-2-(isopropylmethylsilyl)­benzene (<b>2a</b>) in 71% yield, as a single stereoisomer. A similar reaction of <i>trans</i>-benzodisilacyclobutene (<b>1b</b>) with <i>tert</i>-butyl alcohol produced the <i>threo</i> isomer <b>2b</b> in 81% yield, as the sole product. The photolysis of <b>1a</b>,<b>b</b> in the presence of <i>tert</i>-butyl alcohol afforded a mixture of two adducts formed by the reaction of 1-[2-(isopropylmethylsilyl)­phenyl]-1-isopropylsilene with <i>tert</i>-butyl alcohol, respectively. The reaction of <b>1a</b> with ethylene in an autoclave at 300 °C for 24 h gave 3,4,9,10-dibenzo­(r-1)-<i>trans</i>-2,<i>trans</i>-5,<i>cis</i>-8-tetraisopropyl-1,2,5,8-tetrasilacyclododeca-3,9-diene (<b>10a</b>), as a single stereoisomer in 71% yield. The reaction of <b>1b</b> with ethylene under the same conditions, however, produced poly­[1,2-bis­(isopropylmethylsilylene)­phenylene–ethylene], whose molecular weight was determined to be 61000 (<i>M</i>_w/<i>M</i>_n = 2.32), relative to polystyrene standards. The reaction of <b>1a</b> with 1-hexyne, <i>tert</i>-butylacetylene, phenylacetylene, and (trimethylsilyl)­acetylene in benzene in a sealed degassed tube at 150 or 200 °C proceeded stereospecifically to give the respective <i>cis</i>-5,6-benzo-1,4-diisopropyl-1,4-dimethyl-1,4-disilacyclohexa-2,5-diene derivatives (<b>11a</b>–<b>14a</b>) in high yields as the sole products. The reaction of <b>1b</b> with the alkynes under the same conditions afforded the respective <i>trans</i>-benzodisilacyclohexadienes (<b>11b</b>–<b>14b</b>), as the sole stereoisomers in high yields. Theoretical treatment for the reaction of 3,4-benzo-1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene (<b>1c</b>) with <i>tert</i>-butyl alcohol and acetylene indicated that the substrates react directly with <b>1c</b> to give the respective adducts. For the reaction of <b>1c</b> with acetylene, it has been shown that the acetylene molecule inserts directly into a silicon–silicon bond in <b>1c</b> to give the benzodisilacyclohexadiene system. Such direct reactions of the substrates with <b>1c</b> were shown to be energetically more advantageous than the reaction of <i>o-</i>quinodisilane, 1,2-bis­(dimethylsilylene)­cyclohexa-3,5-diene, arising from a conrotatory ring-opening reaction of <b>1c</b> with substrates