Reactions of fused and unfused α-pyrones with magnesium alkoxide, sodium alkoxide and water as the nucleophile: effects of chelation

摘要: The reactions between a series of α-pyrones (two mono- and three fused) the non-chelating base sodium alkoxide, chelating magnesium alkoxide water as nucleophile, have been studied. Aromatic other products formed reflect points attack on pyrone systems when methoxide is used ensuing cyclisation preferentially by aldol mechanisms. employment excess or ethoxide gives magnesium-chelated precursors nature now depends these intermediates, protection afforded such chelation to reaction products. In case structures containing chelated β-keto ester features chelates are screened from acceptors, but effective Claisen acceptors. an adjacent methylene activated further act donor. These contrasting aldol/Claisen reactivities, base, illustrated in chemistry pyrones. Treatment with releases main carbon chain decarboxylation, which new may form.