TRIENEDIOLATES OF HEXADIENOIC ACIDS IN SYNTHESIS - ADDITION TO UNSATURATED-KETONES - A CONVERGENT APPROACH TO THE SYNTHESIS OF RETINOIC ACIDS

The regioselectivity of the addition of the lithium trienediolates gen erated 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 omega carbon, and the ketones according to 1,2- and 1, 4-additions. beta-Ionone 6a and t he aryl-butenone 6b lead to the 1,2-omega-adducts 8, which undergo a f acile acid catalyzed dehydration to retinoic acids 11. On reaction wit h the unsaturated ketone 6b or with the aryl ketones 21, the trimethyl dihydropyran-2-one S leads to gamma'-adducts derived from deprotonatio n of the chain methyl substituent along with the 1,4-omega-adducts.