Preparation of a Select Tautomer of Various Unsymmetrical 1,3,5-Pentanetriones, (1Z,4Z)-1-(Aryl)-1,5-dihydroxy-5-phenylpenta-1,4-dien-3-ones, a 4H-1-benzothiopyran-4-one, and a 2-(2-oxoyl)quinolin-4(1H)-one

Abstract

Deprotonation of 1-benzoylacetone with excess lithium hexamethyldisilazide (LHMDS) or lithium diisopropylamide (LDA) resulted in a dilithium dianion-type intermediate, which underwent a Claisen-type condensation with substituted aromatic esters or an isatoic anhydride to afford unsymmetrical 1,3,5-pentanetriones or a cyclized heterocyclic product when the C-acylated intermediates contained a select ortho-substituted phenacyl pendant group. Spectral data indicated that a particular tautomer, a (1Z,4Z)-1-(4-aryl)-1,5-dihydroxy-5-phenylpenta-1,4-dien-3-one, resulted upon recrystallization of the linear products. Condensation−cyclization of the dianion-type intermediate with methyl thiosalicylate resulted in a phenacyl benzoheterocyclic thiopyranone and with 5-chloroisatoic anhydride in a phenacyl quinolinone. X-ray crystal analysis of several products afforded additional proof of structure, especially regarding which tautomer was isolated.