Synthesis of 1, 4-Diketones from 2-Methyl-2-Vinyl-1, 3-Dioxolane

Abstract

1, 4-Diketones, which are important intermediates for syntheses of jasmones, were prepared from 2-methyl-2-vinyl-1, 3-dioxolane (1) via the radical addition of aldehydes to (1) followed by hydrolysis of ketoacetals.
The radical addition reaction of heptanal (2a) to (1) was carried out with benzoyl peroxide or α, α'-azobisisobutyronitrile as an initiator in N₂ atomosphere at 8085°C. 2, 2-Ethylenedioxy-5-undecanone (3a) was obtained in 57% yield as a major product by this reaction. The by-products in this reaction were 2-methyl-2-octyl-1, 3-dioxolane (5), 7-tridecanol (6), heptanoic acid (7), 2, 2-ethylenedioxy-3-methyl-4-decanone (8), 3, 3-ethylendioxy-1-phenylbutane (9), and 2- (3, 3-ethylendioxybutyl) heptanal (10).
Similarly, 2, 2-ethylenedioxy-cis-8-undecen-5-one (3b), 4, 4-ethylendioxy-1-phenyl-1-pentanone (3c) and 5, 5-ethylenedioxy-2-hexanone (3d) were obtained in 1257% yield.
Hydrolysis of (3a) with 20% H₂SO₄ gave 2, 5-undecanedione (4a) in 95%, yield. Similarly, cis-8-undecene-2, 5-dione (4b), 1-phenyl-1, 4-pentanedione (4c), and 2, 5-hexanedione (4d) were obtained in 9093% yields.