Dioxolanones as synthetic intermediates. Part 2. Synthesis of tetronic acids and pulvinones
The utility of 1,3-dioxolan-4-ones as intermediates in the synthesis of tetronic acids is examined. The reaction of dioxolanone (1) with lithium enolates of 2-substituted methyl or t-butyl acetates at –78 °C in tetrahydrofuran afforded a general synthesis of 2-substituted tetronic acids (3)–(8). Treatment of (1) with the anions of 2-substituted acetonitriles led to formation of the corresponding 3-substituted-2-aminofuran-4(5H)-ones (13) and (14).
A route to unsymmetrically substituted pulvinones by reaction of 5-arylidene-2,2-pentamethylene-1,3-dioxolan-4-ones [5′-arylidenecyclohexanespiro-2′(1′,3′-dioxolan)-4′-ones] with appropriately substituted phenylacetic ester anions has been devised. Thus, the preparation of the naturally occurring pigment 3′,4′,4-trihydroxypulvinone (18) was achieved via an intermediate in which the phenolic groups were protected as benzyl ethers. The dioxolanone (26) has been used in the preparation of 2-acyl-4-benzylidenetetronic acids.