Stereoselective dioxirane hydroxylations and the synthesis of tripod boronic acid esters

Methyl(trifluoromethyl)dioxirane (TFDO, 1b), a powerful yet selective oxidant, was employed to achieve in high yield the direct stereoselective hydroxylation at tert-CH of cis,cis-1,3,5-trimethylcyclohexane (4), yielding triol 7 bearing all-axial disposition of the three OH groups. Similarly, TFDO oxidation of 1,3- and of 1,4-dimethylcyclohexane gave the corresponding Z-diols 5 and 6, respectively. Triol 7 was a convenient starting material to synthesize a novel borate--that is, 1-bora-2,8,9-trioxa-3,5,7-trimethyladamantane (8)--having a peculiar cage-shaped 'tripod' structure. From triol 7, novel tripod arylboronic Brönsted-assisted Lewis acids (BLA) could be obtained, as exemplified by 10a and 10b.