TBAT-catalyzed dioxasilinane formation from beta-hydroxy ketones

Beta-hydroxy ketones can be reduced using a sequence of ruthenium-catalyzed silyl etherification followed by tetrabutylammonium fluoride (TBAF) promoted intramolecular hydrosilylation. Switching from TBAF to tetrabutylammonium difluorotriphenylsilicate (TBAT), even without first forming the silyl ether, gave cyclic dioxasilinane products. These somewhat sensitive compounds could be isolated pure by column chromatography using florisil as the stationary phase. Alternatively, the dioxasilinanes were regioselectively opened with methyl lithium, affording the corresponding differentiated 1,3-diol with selective protection of the secondary alcohol as its diphenylmethylsilyl (DPMS) ether. A mechanism is proposed involving TBAT-catalyzed silyl ether formation followed by TBAT-promoted intramolecular carbonyl hydrosilylation. This mechanism is supported by the observed diastereoselectivity of the reaction, which was consistent with other carbonyl hydrosilylations thought to proceed intramolecularly.