THE 2-HALOGENO-5,6-BENZO-1,3,2-DIOXAPHOSP HORINAN-4-ONE RING-SYSTEM

The reaction of salicylic acid with phosphorus trichloride furnished t he previously known 2-chloro-5,6-benzo-1,3,2-dioxaphosphorinan-4-one h eterocycle 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 reacti ons. The iodo derivative, 4, owing to its instability, could be identi fied only in the reaction mixture by H-1 and P-31 NMR spectroscopy. Th e amine derivatives 5-8 were obtained from 1 using standard exchange r eactions, either with silylated amines or with secondary amines in the presence of base. There was no evidence by H-1 NMR spectroscopy for i ntramolecular Me,N-->P coordination in 6. The P-31 NMR investigation o f 7 revealed the presence of two rotational isomers, presumably as a r esult 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 met hylation at the nitrogen atom of the Me2N group, producing the ammoniu m iodide, 9. The reactions of 5, 6 and 8 with norbornadiene tetracarbo nyl molybdenum failed to furnish isolable products.