The preparation of ethyl and isopropyl dienol ethers and dienol pivalate esters from Hagemann's ester and its t-butyl analogue, and the reactions of the derived ester dienolates with electrophiles

Abstract

The preparation of ethyl 4-ethoxy-2-methylcyclohexa-1,3-diene-1-carboxyate, ethyl 4-isopropoxy- 2-methylcyclohexa-1,3-diene-1-carboxylate, t-butyl 4-isopropoxy-2-methylcyclohexa-1,3-diene-1- carboxylate, ethyl 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate, and t-butyI 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate from Hagemann's ester and its t-butyl analogue in the presence of diethyl or diisopropyl sulfates and sodium hydride in dimethyl sulfoxide, or pivaloyl chloride and N,N,N',N'-tetramethylethylenediamine in tetrahydrofuran is described. The foregoing dienol ethers and esters are smoothly deprotonated by lithium diisopropyl- amide in tetrahydrofuran at -78" to give the corresponding ester dienolates, which react regio- specifically with a number of electrophiles, either a or y to the alkoxycarbonyl group of the dienol ether or ester. A number of the products, which are generally obtained in good yields, have been hydrolysed to Hagemann's ester derivatives substituted exclusively at C1.