Metallated Ketenimines: Quinazoline Derivatives from Base Induced Dimerization of N-Phenyldiethylketenimine. An Experimental and Theoretical Study

Article abstract of DOI:10.1016/0040-4020(95)00514-9

Deprotonation of N-phenyl-diethylketenimine 1 may be achieved by surplus strong organic base (2,2,6,6-tetramethylpiperidine, n-butyllithium, and potassium tert.butoxide in tert.butylmethyl ether).The resulting organometallic suspension is investigated by means of trapping reactions using trimethylacetyl chloride and dimethyl disulfide as electrophiles.From the structures of the trapping products obtained for the first step of the reaction sequence metallation at an aromatic ortho position is deduced.The methylene protons are not affected in the deprotonation.Addition of a second ketenimine 1 leads after ring closure to the heterocyclic anion 9, which is trapped by the electrophiles, yielding the quinazoline derivatives 2-7.The reaction sequence is interpreted in terms of a kinetically accelerated metallation.Semiempirical calculations (MNDO, PM3) of the gas phase acidities of N-phenyl-diethylketenimine 1 support this analysis.Additionally, the quantum chemical results for the optimized structures of the intermediate monomeric lithium compounds 10 and 11 are discussed.