Trienediolates of hexadienoic acids in synthesis. Addition to unsaturated ketones. A convergent approach to the synthesis of retinoic acids

Article abstract of DOI:10.1016/0040-4020(95)00114-N

The regioselectivity of the addition of the lithium trienediolates generated from hexa-2,4-dienoic acids 1 and 2 or the dihydropyran-2-ones 4 and 5 to unsaturated ketones 6 is studied. Equilibration conditions favour reaction of the trienediolates through their ω carbon, and the ketones according to 1,2- and 1,4-additions. β-Ionone 6a and the aryl-butenone 6b lead to the 1,2-ω-adducts 8, which undergo a facile acid catalyzed dehydration to retinoic acids 11. On reaction with the unsaturated ketone 6b or with the aryl ketones 21, the trimethyldihydropyran-2-one 5 leads to γ'-adducts derived from deprotonation of the chain methyl substituent along with the 1,4-ω-adducts.