Synthesis of 9-Alkylated Calcitriol and Two 1 alpha,25-Dihydroxy-9-methylene-10,19-dihydrovitamin D-3 Analogues with a Non-natural Triene System by Thermal Sigmatropic Rearrangements

[摘要]：1 alpha,25-(OH)(2)-9 alpha-Methylvitamin D-3 (4), the first known analogue of the natural hormone 1 alpha,25-(OH)(2)D-3 (3) with an alkyl substituent at C-9, and two 1 alpha,25-(OH)(2)-9-methylene-10,19-dihydrovitamin D-3 analogues (7 and 8) with an unprecedented non-natural triene system were synthesized by thermal isomerization of 1 alpha,25-(OH)(2)-9-methylprevitamin D-3 (6). Three alternative approaches (Sonogashira, Stille, or stereoselective dehydration of a tertiary propargyl alcohol) have been successfully used to construct the dienyne precursors of previtamin 6 possessing two methyl groups capable of participating in the [1,7]-sigmatropic hydrogen shift.

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