SYNTHESIS AND REACTIONS OF ETHYL 6-ARYL-3-ETHOXY-6-OXO-2,4-HEXADIENOATES

Biologically interesting ethyl 6-aryl-3-ethoxy-6-oxo-2,4-hexadienoates (1) have been prepared by the Wittig reaction of yl)-2-ethoxy-2-prope nylidene]triphenylphosphoranes (3a and 3b) and -arsorane (3c) with gly oxal monohydrates (5) and by oxidation of 6-aryl-3-ethoxy-6-hydroxy-2, 4-hexadienoate (9) with activated manganese (IV) oxide supported by si lica. Reaction of 1a with 3c gave 3-(4-chlorobenzoyl)-1,2-trans (and b is(1-ethoxy-2-ethoxycarbonylethenyl)cyclopropanes (6 and 7). When 1a w as treated with a 1: 5 mixture of concentrated HCl and tetrahydrofuran at room temperature, 3-hydroxy-6-oxo-2,4-hexadienoate (10a) was obtai ned in 46% yield. Treatment of 1b with trifluoroacetic acid gave 5,6-d ihydro-2H-pyran-2-one (12) in 53% yield together with 10b in 28% yield . When 1a was treated with 1N ethanolic potassium hydroxide, 12 and 2H -pyran derivative (13) were obtained in 33% and 28% yields, respective ly, Reaction of la with ammonium hydroxide and primary amines in the p resence of a proton acid gave 2-oxo-1,2,5,6-tetrahydropyridines (14) i n good yields. The mechanism of the formation of 6, 12, 13, and 14 is discussed.