A Novel Rearrangement of Allyl Benzyl Ethers and Aspects on the Glyoxylate Ene Reaction

Abstract: This thesis describes an improvement of the glyoxylate ene reaction by using siamyl glyoxaylate and a development of the novel rearrangement of allyl benzyl ethers. The glyoxylate ene reaction was used as a key reaction in a 8-step synthesis of a Taxol A-ring building block. During the work with the ene reaction it was found that the ene component underwent a rearrangement to give arylbutanals in moderate to good yields, when zeolite b was used as catalyst. A few other catalysts such as BF3¥Et2O and Cl2Ti(OiPr)2 also worked but gave inferior yields and more by-products.The mechanism was shown to involve two migrations; a 1,4-migration of the benzylic moietyand a 1,2-hydride (or 1,2-alkyl shift). The reaction was further developed and variation of the substitution pattern at the allylic and benzylic positions showed that the rearrangement was quite general. It was also found that some rearrangement products spontaneously ringclosed to give dihydronaphthalene derivatives. a-Branched allyl benzyl ethers rearranged smoothly, and in one such case an arylnaphthalene skeleton was formed. A short synthesis of the natural product 4-(4-methoxyphenethyl)-cyclohex-2-en-1-one was performed using the rearrangement as a key step.