Enantioselective construction of alicyclic bicyclo[3.1.0]hexane framework by double stereodifferentiation and its application for the synthesis of both enantiomers of vitamin D3 CD ring synthons

Article abstract of DOI:10.1016/S0040-4020(97)00869-7

Good diastereoselectivity (85:15) was observed in the intramolecular cyclopropanation of the chiral unsaturated α-diazo-β-keto ester 9f, which possesses (R)-pantolactone as a chiral auxiliary. The reaction was catalyzed by a chiral bis-oxazoline copper (1) complex 17. The absolute stereochemistry of each generated diastereomer (10f and 11f was elucidated. Both enantiomers of the vitamin D₃ CD ring synthons ((-)-21 and (+)-22) were synthesized from (-)12 and (+)-13, respectively.