Heterocyclization of N-phenylanthranylamide effected by aroyl ketenes

Carboxamides react with aroyl ketenes generated by thermal decarbonylation of 5-aryl-2,3-dihydro-2,3furandiones to afford the corresponding N-aroylacetyl derivatives [1, 2]. Performing the reaction between Nphenylanthranylamide and 5-aryl-2,3-dihydro-2,3furandiones Ia–Ic under conditions of the thermal decarbonylation of the latter we unexpectedly obtained (E)-2-aroylmethylene-1-phenyl-1,2,3,4-tetrahydroquinazolin-4-ones IIa–IIc. The spectral characteristics of quinazolinones IIa–IIc showed that both in the crystalline state and in solutions the compounds exist as E-isomers with a strong intramolecular hydrogen bond of an H-chelate type between the N3–H group and the carbonyl in the side chain. Apparently in the first stage of the reaction occurring along the scheme similar to the above described intermediately form N-aroylacetyl derivatives IIIa–IIIc suffering dehydration under the existing reaction conditions. The relatively low yield of compounds IIa–IIc may be due to the reaction of water eliminated during this dehydration with one of the reagents, furandione Ia–Ic (see Scheme). This reaction is a convenient one-stage preparative method for representatives of a hard-to-obtain class of heterocyclic enaminoketones. (E)-2-Phenacylidene-1-phenyl-1,2,3,4-tetrahydroquinazolin-4-one (IIa). A solution of 10 mmol of 5-diketone Ia and 10 mmol of N-phenylanthranylamide in 25 ml of anhydrous benzene was boiled for 3 h, then cooled, the solvent was distilled off till the solution volume 10 ml, the solution was cooled, and the precipitate was filtered off. Yield 44%, mp 299–300°C (decomp., from