Wittig rearrangement of furylmethyl ethers and application to natural product synthesis

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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.