Dioxolanones as synthetic intermediates. Part 3. Biomimetic synthesis of pulvinic acids
The reaction of the phosphorane (16) with methyl arylglyoxylates gives 5-(α-methoxycarbonyl-arylidene)-2,2-pentamethylene-1,3-dipxolan-4-ones [5′(α-methoxycarbpnylarylidene)cyclohexane-spiro-2′-(1′,3′-dioxolan)-4′-ones] which have been treated with the lithium enolates of t-butyl phenylacetic esters to provide a biomimetic synthesis of pulvinic acids. By this method pulvinic acid (2), vulpinic acid (1), and the unsymmetrically substituted compounds, leprapinic acid (3), and xerocomic acid (4) have been prepared; the last named was obtained via an intermediate (28) in which the phenolic groups were protected as benzyl ethers.