A variety of routes are described for the synthesis of a-silyloxy aldehydes in which the silicon atom bears a prenyl side chain. These compounds are shown to undergo stereoselective carbonyl ene cyclisation under mildly Lewis acidic conditions and the derived silacycles are cleaved to afford single diastereomers of functionalised triols.

[reaction: see text] We describe two applications of silicon-tethered thermal allyl transfer reactions of alpha-silyloxyaldehydes; formally, these processes can be regarded as silatropic carbonyl ene reactions in which the silicon tether is transferred to the aldehyde oxygen concurrent with carbonyl allylation. In the first application, isoserinal substrates, which bear side-chain nitrogen functionality, are elaborated to dihydroxypiperidines. In the second application, a product of cyclohexadienyl transfer is taken on to carbocylic analogues of, for example, mannose. In both series, the silatropic ene reactions are effected thermally, with no added Lewis acid, and are both stereospecific and highly stereoselective.

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Organo-silicon compoundsOrgano-silicon compounds S 0060Ene Cyclizations of α-(Prenyl)dialkylsilyloxy Aldehydes: Formation and Oxidative Cleavage of Oxasilacyclohexanols. -α-silyloxy aldehydes which are generated by different routes are found to undergo stereoselective ene cyclization to oxasilacyclohexanols. In one case formation of a siladioxolane is also observed via competing allylic transfer. The oxasilacyclohexanols smoothly undergo ring opening in the presence of H 2 O 2 yielding chiral functionalized triols which are useful synthons. -(ROBERTSON*, J.; HALL, M. J.; STAFFORD, P. M.; GREEN, S. P.; Org. Biomol.