Acyl Anion Equivalents for 1,2-Alkylative Carbonyl Transpositions

3 Acyl Anion Equivalents for 1,2-Alkylative Carbonyl Transpositions 

2-alkylative carbonyl transpositions where the carbonyl group moves forward into the newly added fragement, e. g. 63 - 64, the reagent behaves as an acyl anion equivalent. We have seen one example of this in the synthesis of the occidentalol intermediate 8. Phosphine oxides with OR or SR substituents on the a-carbon 65 are ideal reagents for this process as the Horner-Wittig reaction gives vinyl compounds which can be hydrolysed to 64. 

The classical solution to this problem is the decarboxylation of glycidic acids37-1 66, used by Woodward38 in his Lysergic acid synthesis. The Wittig reaction was 

Phosphine oxide anions are often superior to ylids in olefmation reactions, and the anion of 68, made with lithium di-isopropyl-amide (LDA), has none of the disadvantages of the ylid 67. We have made 41 a range of vinyl ethers 70 this wayc, and as part of a synthesis of stiychnos alkaloids43, we were able41 to convert the acyl indole 71 into the aldehyde 72 

One advantage of this route is that the vinyl ethers can be synthesised as single geometrical isomers by separating the diastereoisomers of 69 and converting each separately into the vinyl etherd. These vinyl ethers form anions which have been used in synthesis45. The trans vinyl ether -73 tends to form the vinyl anion46  

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