A ONE-POT CONDENSATION OF PYRONES AND ENALS - SYNTHESIS OF ,6,8,9-TETRAHYDRO-1-OXOPYRANO[4,3-B][1]BENZOPYRANS

Condensation of various 6-substituted 4-hydroxypyrones 1 with 1-cycloh exenecarboxaldehydes in the presence of L-proline in ethyl acetate gav e high yields of substituted 6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]ben zopyrans. The reaction presumably occurs via the 1,2-addition of the p yrone with the aldehyde followed by dehydration and then cyclization t hrough a 6 Pi electrocyclic process. A remarkable asymmetric induction was obtained from a stereogenic center (C4) of the cyclohexenecarboxa ldehyde [such as (S)-perillaldehyde] to provide only the C5a,7-trans t ricyclic pyrone products. On the other hand, condensation of S-(formyl oxy)- or 3-hydroxy-2-methyl-1-cyclohexene-carboxaldehydes with pyrones 1 gave mixtures of C5a,6-cis and -trans products. Several of the tric yclic pyrones strongly inhibit acetylcholinesterase activity, DNA synt hesis, and tumor cell growth in vitro.