Abstract
An efficient one-pot multi-component reaction for the diastereoselective synthesis of novel trans-4,4a-dihydro-3H-benzo[4,5]oxazolo[3,2-a]pyridines starting from readily available cinnamaldehydes, o-aminophenol and 1,3-dicarbonyl compounds/ ethyl propiolate catalysed by AcOH is described. The products could be obtained in 3 h under refluxing conditions with perfect diastereoselectivity. Single crystal X-ray analysis confirmed the trans-derivative as the only isomer. All the compounds were unequivocally confirmed by NMR, HRMS and XRD analysis. To discuss the special pattern of methylene protons (H8a: td and H8b: dt) on the NMR of the compound 4a, NMR spectra analysis (1D-NMR and 2D-NMR) was conducted in details by the chemical shifts, couplings and correlations. XRD analysis of 4a and 6a further aids to disclose the spatial effect of methyl group on the geometry of the tetrahydropyridine rings of the compounds.
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