文档介绍：方法一:2和3经叶立德反应得到最终产品从Vitamin D2 合成片段31,of vitamin D2 6经KMnO4 氧化的7:2,7经Mitsunobu反应得到8;3,8用SeO2氧化,得到9;4,9用TMS保护的105,10经水解得到11,6,11用TMS保护得到127,12氧化裂解后在氢化还原为13,8,13经过一步氧化得到3片段片段22的合成的合成A new enantioselective synthesis of the building block 2 was developed based upon the asymmetric Mukaiyama–Michael Optically active thioester?14 (96% ee, Scheme 3), was treated with LDA and then with TMSCl to give ketene acetals15. The latter were allowed to react with enone5 in the presenceof 5 mol% of TrSbCl6. When the majority of the reagents were consumed, the second Michael acceptor 16 was Thereaction product consisted of three diasteromers in a ratio of 85:11:4 (by HPLC). All our attempts to separate the ponent, to which structure 17 was later assigned, failed. The mixture was subjected to cyclization to give 18 along with minordiastereomers. After NaBH4–CeCl3 reduction21 of these a,b-unsaturated ketones a crystalline material was obtained, which was recrystallized to afford allylic alcohol 19 in a 53% yield from 17. The structure of 19 was determined by X-ray contrast to Kocienski’s23 procedure for executing the Julia alkylation, the coupling of sulfone2 and aldehyde3 was plished using an excess of the sulfone. Treatment of 2, in THF, with BuLi ( mol equivalent), at ?20°C, followed with a mixture of 3 and 3a ( mol equivalents), at?78°C, afforded the adduct which was quenched with AcCl. The crude product 23was then reduced with 6% sodium amalgam in methanol in the presence24 of Na2HPO4. A mixture of silyloxy and acetoxytrienes24 was obtained in a 25% overall yield from 3. This mixture was allowed to react with TBAF·3H2O in THF and then with methanolic KOH to give the respective trihydroxytrienes as a mixture of geometric isomers25 in a ratio of 94:5:1. Themajorisomer, ent-1, was separated by preparative HPLC. Its retention time on an analytical olumn was the same as that of natural 1a,25-dihydroxyvitaminD3 and the 1H NMR spectrum was