Reactions of Umpolung Reagents with Enol Ethers of β-Diketones: Sterically Induced Selectivity of the Dithiane Anion

Article abstract of DOI:10.1021/jo01295a018

In work on the synthesis of a tricyclic analogue of daunomycinone, the reactions of several umpolung equivalents of acetaldehyde with enol ether esters of 3,5-dioxocyclohexanecarboxylic acid have been examined.The dithiane reagent 1 and the sulfoxide 2 give 1,2 attack on the carbonyl group of the vinylogous ester system and also react at a similar rate with ester groups.The latter reaction can be retarded by using esters formed with isobutyl rather than methyl alcohol.In order to get selective attack on the carbonyl of the vinylogous esters in preference to thatof the ester, it is best to use reverse addition at low temperature.