Intramolecular [4 + 2] Cycloaddition Reactions of Ketenimines: A New Synthesis­ of Benz[b]acridines

Abstract

N-[2-(2-Propenyl)phenyl]-C,C-diphenyl ketenimines undergo a thermally induced intramolecular [4 + 2] cycloaddition to give 5,11,11a,12-tetrahydrobenz[b]acridines, which are converted into the fully aromatic benz[b]acridines by oxidation with Pd/C in refluxing ortho-xylene.

Key words

azides - acridines - cycloadditions - polycycles - ketenimines - phosphazenes

References

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8

Compound 2 ³¹P NMR (121.4 MHz, CDCl₃): δ = 1.29.

9

The heating of the toluene solutions of the ketenimines 10 at 130 °C in a sealed tube gave mixtures of 5,11,11a,12-tetrahydro, 5,12-dihydro and the fully aromatic 11-aryl-6-phenylbenz[b]acridines, and the same results were obtained when this thermal treatment was carried out in the presence of Pd/C.