A biocatalytic/reductive etherification approach to substituted piperidinyl ethers

A synthetically useful protocol has been developed for the preparation of highly functionalized piperidinyl ethers. Biocatalytic reduction of cyclhexanones 7, 10, and 14 allows for the preparation of both cis- and trans diastereomers with an extremely high degree of stereochemical control. Reductive etherification of the corresponding trimethylsilylethers with 1-(benzyloxycarbonyl)-4-piperidinone 17 in the presence of triethylsilane and catalytic TMSO-Tf provides the desired piperidinyl ethers in good to excellent yields. Finally hygrogenolysis of the nitrogen protecting group leads to piperidinyl ethers in near quantitative yields. Application of the methodology to a range of piperidinyl ethers, including the core scaffolds of diphenylpyraline and ebastine, is also described.