SYNTHESIS AND REARRANGEMENT OF 2,3,5,6-TETRAKIS(ISOPROPYLIDENE)-1,4-DIBORACYCLOHEXANE AND 2,3-BIS(ISOPROPYLIDENE)-1,4-DIBORACYCLOHEXANE DERIVATIVES

2,3,5,6-Tetrakis(isopropylidene)-1,4-dimethyl-1,4-diboracyclohexane (1c) is formed in 66% yield from 3,4-bis(chloromethylboryl)-2,5-dimethyl-2-4-hexadiene (4a) and (Me(2)C=CLi)(2). Surprisingly, 1,4-dichloro-2,3,5,6-tetrakis(isopropylidene)1,4-diboracyclohexane (1d) is obtained in 38% yield, when tetrabutyltin and 3,4-bis(dichloroboryl)-2,5-dimethyl-2,4-hexadiene (4b) are heated. Reactions of 1,2-bis(chloromethylboryl)ethane derivatives 5a, b with (Me(2)C=CLi)(2) lead to the 2,3-bis(isopropylidene)-1,4-diboracyclohexanes 6a, b in 41 and 35% yield. The irradiation of 6 a, b and Ic, d with ultraviolet light induces an antarafacial [1,5]-H-shift which leads to the formation of the diboracyclohexenes 7a, b and 8a, b, as indicated by NMR studies. On further irradiation 8a, b rearrange to form the corresponding nido-C4B2 carboranes 9a, b. The constitutions of the compounds are derived from spectroscopic data and are proven by X-ray structure analyses of Ic, d, e.