1,4-Chirality transfer via the ester enolate Claisen rearrangements in the preparation of (25R)- and (25S)-cholestenoic acids.
Steroids
; 78(7): 683-92, 2013 Jul.
Article
in En
| MEDLINE
| ID: mdl-23583600
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.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Cholestenes
Language:
En
Journal:
Steroids
Year:
2013
Document type:
Article
Affiliation country:
Belarus