1996 Volume 44 Issue 5 Pages 885-891
Biologically interesting ethyl 6-aryl-3-ethoxy-6-oxo-2, 4-hexadienoates (1) have been prepared by the Witting reaction of [3-(ethoxycarbonyl)-2-ethoxy-2-propenylidene]triphenylphosphoranes (3a and 3b) and -arsorane (3c) with glyoxal monohydrates (5) and by oxidation of 6-aryl-3-ethoxy-6-hydroxy-2, 4-hexadienoate (9) with activated manganese (IV) oxide supported by silica. Reaction of 1a with 3c gave 3-(4-chlorobenzoyl)-1, 2-trans (and cis)-bis(1-ethoxy-2-ethoxycarbonylethenyl)cyclopropanes (6 and 7). When 1a was treated with a 1 : 5 mixture of concentrated HCl and tetrahydrofuran at room temperature, 3-hydroxy-6-oxo-2, 4-hexadienoate (10a) was obtained in 46% yield. Treatment of 1b with trifluoroacetic acid gave 5, 6-dihydro-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, respectively. Reaction of 1a with ammonium hydroxide and primary amines in the presence of a proton acid gave 2-oxo-1, 2, 5, 6-tetrahydropyridines (14) in good yields. The mechanism of the formation of 6, 12, 13, and 14 is discussed.
