First Diels-Alder Cycloaddition of N'-Oxazolyl-N,N-dimethylalkylamidines with Electron-Poor Dienophiles: Characterization of a Diastereoselective Pathway

Diels-Alder cycloaddition of N'-oxazolyl- N, N-dimethylalkylamidines 1a, b with electron-poor dienophiles were performed, leading to new 2-phenoxymethyl-6-formyl-2,3-dihydro-5 H-oxazolo[3,2- a]pyrimidines and 2-phenoxymethyl-6-nitro-2,3-dihydro-5 H-oxazolo[3,2- a]pyrimidines. The regio and endo diastereoselectivity of one [4+2] cycloadduct 4 was established through the single-crystal X-ray structure determination of 4a. The diastereoselectivity could be related to a potential π-stacking interaction.