Das 2-Halogen-5,6-benzo-1,3,2-dioxaphosphorinan-4-on-Ringsystem / The 2-Halogeno-5,6-benzo-1,3,2-dioxaphosphorinan-4-one Ring System

Abstract

The reaction of salicylic acid with phosphorus trichloride furnished the previously known 2-chloro-5,6-benzo-1,3,2-dioxaphosphorinan-4-one heterocycle 1 which was unambiguously characterized, for the first time, by NMR spectroscopy and mass spectrometry. The fluorine and bromine analogues of 1, 2 and 3 were synthesized from 1, using exchange reactions. The iodo derivative, 4, owing to its instability, could be identified only in the reaction mixture by 1H and 31P NMR spectroscopy. The amine derivatives 5-8 were obtained from 1 using standard exchange reactions, either with silylated amines or with secondary amines in the presence of base. There was no evidence by 1H NMR spectroscopy for intramolecular Me2N→P coordination in 6. The 31P NMR investigation of 7 revealed the presence of two rotational isomers, presumably as a result of steric hindrance at the P–N bond by the methyl substituent of the piperidine group. The reaction of 6 with methyl iodide led to methylation at the nitrogen atom of the Me2N group, producing the ammonium iodide, 9. The reactions of 5,6 and 8 with norbornadiene tetracarbonyl molybdenum failed to furnish isolable products.