Palladium(II)-assisted [2+3] cycloaddition of nitrones to organonitriles: Synthesis of 2,3-dihydropyrrolo[1,2-a]quinazolin-5-one and Δ4- 1,2,4-oxadiazoline derivatives

Abstract

The [2+3] cycloadditions of different organonitriles NCR (R1 = C6F5, R2 = Pr, R3 = p-CHOC 6H4, R4 = Ph) with the cyclic nitrone or acyclic nitrone -O+N(Me)C(H)(C6H 2Me3-2,4,6), in the presence of PdCl2, give the corresponding fused tricyclic fluorinated ketoimine trans- (1), fused bicyclic Δ4-1,2,4-oxadiazoline trans- (R2 = Pr (2), R 3 = p-CHOC6H4 (3)) or monocyclic Δ4-1,2,4-oxadiazoline trans- (4) palladium(II) complexes. The free tetrafluoro-2,3-dihydropyrrolo[1,2-a]quinazolin-5-one (1a) and Δ4-1,2,4-oxadiazolines (2a-4a) are liberated upon reaction of complexes 1-4 with a diphosphine (dppe). All the compounds were characterized by elemental analyses, ESI+-MS, IR, 1H and 13C NMR spectroscopies. © 2013 Elsevier Ltd. All rights reserved.