19‐Nor‐vitamin D A‐ring synthons were obtained from linear olefins by means of ring‐closing olefin metathesis followed by palladium‐catalyzed isomerization of the endocyclic olefin product to an exocyclic olefin.
1a-Amino-25-hydroxyvitamin D 3 is of interest because of its low calcemic effect in vivo comparedt o1 ,25-dihydroxyvitamin D 3 and its characteristicinhibitory activity towards sterol regulatory elementb inding protein (SREBP), aregulator of lipogenesis. Here we describe the construction of an ovel A-ring synthon bearing an allylic amine, in which the key reaction is an Ichikawa rearrangemento fa llyl cya-nate generated from an allylic alcohol, which wasd erived from l-malic acid. The diastereomers were separated by silica-gel chromatography,a nd ap alladium-catalyzed coupling reactiono fe ach diastereomer with the CD-rings ynthon afforded 1a-amino-25-hydroxyvitamin D 3 and 1bamino-25-hydroxyvitamin D 3 ,r espectively.Scheme1.Convergent strategy for synthesis of 1a-amino-25-hydroxyvitamin D 3 (2).Scheme2.Synthesis of allylic alcohol 11. Scheme3.Preparation of A-ring precursor 13.
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