REACTIONS OF CYCLIC OXALYL COMPOUNDS .34. SYNTHESIS OF DIBENZOYLACETATE-N-CARBOXYALKYLAMIDES AND SEMIEMPIRICAL CALCULATIONS OF KETO-ENOL TAUTOMERS

4-Benzoyl-5-phenylfuran-2,3-dione (1) and the urethanes 2 combine under loss of carbon monoxide yielding the open chain dibenzoylacetic acid derivatives 3 and 4. 3a, b only can be cyclized to the oxazinone 5. The keto-enole tautomerism 3 half arrow right over half arrow left 4 is further investigated with aid of semiempirical quantum chemical calculations, based upon the molecular geometry of 3a, deduced from an X-ray study