Reaction of Electron-Deficient 3-Acetyl-1-arylpent-2-ene-1,4-diones as a Building Block of Heterocycles

The BF3-assisted reaction of 3-acetyl-1-arylpent-2-ene-1,4-diones 1a-c with cyclohexanones and piperidin-4-ones 2a-i gave unique 3a,6a-dihydrospirofuro[2,3-d][1,3]dioxoles 3 in good to high yields. A similar reaction with the 2,3-dihydroquinolin-4(1H)-ones did not occur, but the reaction with 4-hydroxychromenone 5 mainly produced 3-furfuryl-4-hydroxychromenone 6 along with furochromenone 7. The reaction of the electron-deficient pentenedione la as a Michael acceptor with indole, pyrrole, furan, and N-methylaniline produced the corresponding 1,4-adducts. Especially, the indole adduct was easily converted by the Paal-Knorr synthesis into the corresponding furanyl-, pyrrolyl-, and thiophenyl-substituted indoles. The reaction details and the structure determination of the products are described.