title: 1,4-Chirality transfer via the ester enolate Claisen rearrangements in the preparation of (25R)- and (25S)-cholestenoic acids.
abstract: Two variants of the Claisen rearrangement were evaluated for a stereoselective construction of a C-25 stereogenic center in cholestenoic acids based on 1,4-chirality transfer. Johnson orthoester Claisen rearrangement of (22R)- and (22S)-propargyl enol ethers proceeded in a highly stereoselective manner to give (25R)- and (25S)-isomeric allenes. The stereochemical outcome of the Ireland-Claisen rearrangement of 22-allylic alcohols was dependent on the configuration of the C-22 hydroxyl group and the geometry of the enol ether. The latter could be controlled by the solvent (THF or a mixture of THF/HMPA) chosen for the generation of silyl enolate.
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str. 5/2, 220141 Minsk, Belarus.
authors.forename: Yurii V
authors.initials: YV
authors.lastname: Ermolovich
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Zhabinskii
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Khripach
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000737:chemistry; D002782:Cholestenes / Q000737:chemistry*; D006492:Hempa / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D002782:Cholestenes; C514718:cholestenoic acid; D015761:4-Aminopyridine; D006492:Hempa; C003885:4-dimethylaminopyridine