Enantioselective protonation of the lithium transient enolate of 2-methyltetralone with 2-sulfinyl alcohols

A new catalytic cycle for the enantio selective protonation of cyclic ketone enolates with sulfinyl alcohols has been developed. An enol trifluoroacetate that can be easily obtained from the corresponding ketone is used for the first time as an enolate precursor of a cyclic ketone enolate. In this method, the achiral alcohol plays two roles: it is involved, as is usual in catalytic asymmetric protonation reactions, in the turnover of the chiral proton source and also in the generation of a transient enolate through the reaction of its corresponding alkoxide with the enol trifluoroacetate precursor. Stereoselectivity is highly dependent on the structure of the achiral alcohol. High levels of stereoselectivity can be achieved with the use of cyclohexanol. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).