A mild method for α-hydroxylation of N-acyl oxazolidinones by asymmetric radical addition of the 2,2,6,6-tetramethylpiperidine N-oxy (TEMPO) radical to titanium enolates was developed. The high diastereoselectivity and broad scope of the reaction show synthetic utility for the α-hydroxylation of substrates that are not tolerant to strongly basic conditions.

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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.

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