Synthesis and NMR Spectral Properties of Phosphines in the 2-Phosphabicyclooct-5-ene and 2-Phosphabicycloocta-5,7-diene Systems

Article abstract of DOI:10.1021/jo00243a023

1,6-Dihydrophosphorin 1-oxides were synthesized by dehydration of 3-hydroxy-1,2,3,6-tetrahydrophosphorin 1-oxides; Diels-Alder reactions with maleic acid derivatives gave the 2-phosphabicyclo<2.2.2>oct-5-ene ring system, while reaction with dimethyl acetylenedicarboxylate gave the corresponding octa-5,7-diene system.The latter system was also approached by lead tetraacetate oxidation of a dicarboxylic acid in the oct-5-ene system.Removal of the phosphoryl oxygen required very gentle conditions with the dienes to prevent fragmentation.This was accomplished with trichlorosilane at -8 to 0 deg C.The dienic phosphines were stable at 0-25 deg C but lost the P-containing bridge at 30-50 deg C.The 31P NMR shifts of all compounds were normal and resembled monocyclic phosphorin models.This ring structure, either with one or two double bonds, therefore does not cause the strong deshielding so characteristicof the related 7-phosphanorbornene system.To interpret the 1H and 13C NMR spectra of the dienic phosphines, 2-D techniques were used.