RULES FOR RING CLOSURE: APPLICATION TO INTRAMOLECULAR ALDOL CONDENSATIONS IN POLYKETONIC SUBSTRATES

Article abstract of DOI:10.1016/0040-4020(82)85023-0

An extension of the nomenclature for classifying ring closures to include intramolecular reactions of enolate anions is described, and the rules governing such cyclizations are enumerated.The syntheses of the polyketonic substrates 4-acetyl-2,6-heptanedione (11), 4-acetyl-4-methyl-2,7-octanedione (24), and 3-acetyl-3-methyl-1,6-diphenyl-1,6-heptanedione (33) were carried out, and their base-induced intramolecular aldol condensations studied.With each substrate a favored 6-(enolendo)-exo-trig cyclization to produce cyclohexenone products was the only ring forming reaction observed, this process predominating in all instances over competing disfavored 5-(enolendo)exo-trig closures, and also over other competing favored cyclizations.The identity of the cyclization product 12 derived from 11 was confirmed by aromatizing 12 to 17, and alternately synthesizing 17 from 3-bromo-5-methylphenol.