STUDIES ON VITAMIN-D (CALCIFEROL) AND ITS ANALOGS .37. A-HOMO-11-HYDROXY-3-DEOXYVITAMIN-D - RING SIZE AND PI-FACIAL SELECTIVITY EFFECTS ON THE [1,7]-SIGMATROPIC HYDROGEN SHIFT OF PREVITAMIN-D TO VITAMIN-D

被引:22
作者
ENAS, JD [1 ]
PALENZUELA, JA [1 ]
OKAMURA, WH [1 ]
机构
[1] UNIV CALIF RIVERSIDE, DEPT CHEM, RIVERSIDE, CA 92521 USA
关键词
D O I
10.1021/ja00004a043
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The previtamin D-vitamin D interconversion, a [1,7]-sigmatropic hydrogen shift, provides a convenient system with which to evaluate the structural requirements of this hydrogen migration process. Thus, the A-homoprevitamin D analogues 7a,b and 8a,b were synthesized and their thermal [1,7]-sigmatropic hydrogen rearrangements studied. Relative to the parent previtamin D3 system, the presence of the seven membered A-ring not only accelerates the rate of the rearrangement but also shifts the equilibrium to lie completely in favor of the vitamin. In addition, the 11-hydroxyl group was found to exert a modest effect (approximately 2:1 to approximately 5:1) on the preferred helicity of the antarafacial rearrangement (a pi-facial selectivity effect). In both cases a syn directive effect by the 11-hydroxyl was observed.
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页码:1355 / 1363
页数:9
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