Dienediolates from unsaturated carboxylic acids. Reaction with para-substituted benzaldehydes. Electronic effects on regioselectivity

Regioselectivity α/γ ratios for addition of the lithium dienediolate of crotonic acid to para-substituted benzaldehydes are subject to small electronic effects when reactions are carried out at low temperature, but strong influence by substituents is observed on heating for 1 h at 60 °C. A linear correlation is then found between regiochemical ratios and σp parameters. Stereoselectivity RR/RS ratios (33 : 66 to 43 : 57) for α-adducts obtained in the cold do not depend on the substituents.