Stereochemistry of the reaction of oxygen nucleophiles with a phosphinous chloride in the 7-phosphanorbornene series

Dimers of 1-aminophosphole oxides react with trichlorosilane–pyridine at the 7-phosphanorbornene moiety to provide the anti-chloro derivative, useful for preparing other compounds. With sodium methoxide, chlorine displacement occurs smoothly to give exclusively the anti-phosphinite. This ester has been treated with benzyl and methyl halides to give tertiary phosphine oxides. The chloro compound reacts with methanol to give the same phosphinite, along with some of the secondary phosphine oxide from cleavage of the methyl group. The secondary phosphine oxide, with anti-oxygen, is the exclusive product of the hydrolysis of the chloride. The complete retention of configuration in these reactions, also observed previously in arylation with phenyl Grignard reagent and in a bromide-exchange reaction, is consistent with a mechanism involving a phosphoranide intermediate whose decay is governed by rules laid down for true trigonal bipyramidal intermediates.