Wittig rearrangement of furylmethyl ethers and application to natural product synthesis

通过2-呋喃甲醚的Wittig重排进行了手性转移。(2S，3Z)-和(2S，3E)-3-戊烯-2-基醚经完全手性转移重排，分别得到(1R，2S，3E)-和(1R，2R，3E)-1-(2-furyl)-2-methyl-3-penten-1-ols，。以16-呋喃甲氧基类固醇的Wittig重排为关键步骤，完成了蜕皮酮、胡芦巴内酯和油菜素内酯等甾体侧链的立体选择性构建。(17E)-16-α-和(17Z)-16-β-Furyoxy-6-β-甲氧基-3α，5-环-5-α-17-烯的Wittig重排分别得到(20S，22S，23Z，25Z)-和(17Z)-5-α-Cholesta-16，23，25-三烯。具有20S和22S立体化学结构的甾体可以转化为蜕皮酮和内酯侧链，而(20S，22R)-异构体则会生成油菜素内酯侧链。利用环呋喃醚的分子内Wittig重排反应合成了拟蕨类内酯的核心。其主要特征是(5E)-5-甲基-3，16-二氧二环[11.2.1]十六碳-1(15)，5，13-三烯的非对映选择性Wittig重排，为(2R^*，3R^*)-3-异丙基-13-氧双环[8.2.1]十三碳-1(12)，10-二烯-2-醇在目标分子的C1和C2位置提供了正确的立体化学。

Chirality transfer via the Wittig rearrangement of 2-furylmethyl ethers has been carried out. Both (2S,3Z)-and (2S,3E)-3-penten-2-yl ethers rearranged with complete chirality transfer to give (1R,2S,3E)-and (1R,2R,3E)-1-(2-furyl)-2-methyl-3-penten-1-ols, respectively.Stereoselective construction of steroidal side chains, such as ecdysone, withanolide, and brassinolide, has been accomplished employing the Wittig rearrangement of 16-furfuryloxy steroids as a key step. Wittig rearrangement of (17E)-16α-and (17Z)-16β-furfuryloxy-6β-methoxy-3α, 5-cyclo-5α-pregn-17-enes proceeded stereoselectively to afford (20S,22S,23Z,25Z)-and (20S,22S,23Z,25Z)-23,26-epoxy-22-hydroxy-6β-methoxy-3α, 5-cyclo-27-nor-5α-cholesta-16,23,25-trienes, respectively. Steroid possessing 20S and 22S stereochemistries could be transformed into ecdysone and withanolide side chains, whereas (20S,22R)-isomer would lead to brassinolide side chain.Studies toward the synthesis of the core of pseudopterolide have been carried out by the utilization of the intramolecular Wittig rearrangement of cyclic furfuryl ether. The key feature is the diastereoselective Wittig rearrangement of (5E)-5-methyl-3,16-dioxabicyclo [11.2.1] hexadeca-1(15), 5,13-triene providing (2R^*,3R^*)-3-isopropyl-13-oxabicyclo [8.2.1] trideca-1(12), 10-dien-2-ol with the correct stereochemistries at the C1 and C2 positions of the target molecule.