An efficient asymmetric synthesis of 1.alpha.,25-(OH)2 vitamin D3 A-ring synthon
摘要:
Chiral synthesis of the A-ring synthon 3 of 1alpha,25-dihydroxyvitamin D3 (1a) based on palladium-catalyzed cyclization of 8-bromo-2,8-nonadienoates is described. Reaction of (E)-4b and (Z)-4d in the presence of Pd(OAc)2, PPh3, and K2CO3 gave (E)-3b and (Z)-3d, respectively. Optically active 4d was prepared from 24 by asymmetric aldol reaction using 31, which was cyclized to 3d. With further reactions, 1alpha,25-dihydroxyvitamin D3 (1a) was obtained.
An efficient asymmetric synthesis of 1.alpha.,25-(OH)2 vitamin D3 A-ring synthon
摘要:
Chiral synthesis of the A-ring synthon 3 of 1alpha,25-dihydroxyvitamin D3 (1a) based on palladium-catalyzed cyclization of 8-bromo-2,8-nonadienoates is described. Reaction of (E)-4b and (Z)-4d in the presence of Pd(OAc)2, PPh3, and K2CO3 gave (E)-3b and (Z)-3d, respectively. Optically active 4d was prepared from 24 by asymmetric aldol reaction using 31, which was cyclized to 3d. With further reactions, 1alpha,25-dihydroxyvitamin D3 (1a) was obtained.
A novel asymmetric synthesis has been developed for the construction of the A-ring of a chiral precursor to calcifediol. The highlights of this synthesis include (i) the introduction of the stereochemistry at the C5-position of the A-ring through the organocatalytic enantioselective desymmetrization of a prochiral cyclicanhydride using a bifunctional urea catalyst and (ii) the introduction of the
Palladium-catalyzed cyclization of 8-bromo-2,8-nonadienoates proceeded stereoselectively to give 1-alpha-hydroxyvitamin D3 A-ring synthons in good yields.