Acyclic isoprenoid 1,3-dieneamines in the Diels-Alder reaction

Abstract

The dieneamines obtained from 3-methyl-2-butenal and citral (Ia) and (Ib, c) enter into [4 + 2]-cycloaddition with monoethyl citrylidenemalonate (II) and prenylidenemalonate (III), respectively, forming the esters of substituted 1,3-cyclohexadiene-1-carboxylic acids with side chains of the isoprenoid type. The same or analogous cyclohexadiene can be obtained from “citral dieneamine” (Ib, c) and typical dienophiles (methyl acrylate, diethyl fumarate, etc.) in a two-stage path, including the initial production of derivatives of 2-amino-3-cyclohexene-1-carboxylic acid in the Diels-Alder reaction and then elimination of the amino group from the cyclic adducts. The isomeric composition of the mixture of cyclic adducts formed in the reaction of (Ib + Ic) with diethyl fumarate under strictly aprotic conditions correlates with the ratio of the structural isomers with a δ3 and δ3(9) bond (Ib, c) in the “citral dieneamine.” In the reaction of the dieneamine with the less reactive methyl acrylate the obtained mixture of cyclic adducts contains a significantly larger fraction of the isomer corresponding to the minor δ3(9) isomer of the dieneamine.