Methyl arylphosphinate

The most efficient synthetic route was a condensation of methyl arylphosphinates 283 with oxazolidine 280. Precursors 283 were prepared by esterification of corresponding phosphinic acid, using a procedure described by Afarinkia (Scheme 56) [201]. When //-phosphinic acids were not commercially available, they were obtained by pallado-catalyzed arylation of anilinium hypophosphite [202]. The condensation gave a mixture of two diastereomers synlanti). The last step was selective epimerization at the phosphorus atom in concentrated HCl. 

Catalysts which have been found to promote dimerization of phenyl isocyanate include pyridine (11), methylpyridine (12), triethylamine (13), X-methyl- (or ethyl-)morpholine, triethylphosphine, and other alkyl or alkyl-arylphosphines (14, 15). Alkylphosphines bring about a very violent polymerization since they act as active catalysts and the polymerization is quite exothermic. Triphenylphosphine is inactive. Alkyl-arylphosphines are not as active as alkylphosphines and permit better control of the reaction. Another convenient method (14, 16) for control of phosphine-catalyzed dimerization involves the addition of an alkylating agent such as benzyl chloride in an amount stoichioraetrically equivalent to the substituted phosphine present. Complete deactivation of the catalyst results. By this means the reaction may be mitigated or even quenched and then activated by the addition of more catalyst. 

The structures of fluorophosphine, PH2F, and chlorophosphine, PH2CI, have been determined by ab initio calculations, and the pyramidal geometry of the X Ai ground state of the Pp3 cation has been confirmed. An ab initio study of the internal rotation levels of the terminal methyl group in the ethylphosphine molecule CH3CH2PH2 has been undertaken. Ab initio calculations on ethyldi-fluoro-, ethyldichloro-, and ethyldimethyl-phosphines, CH3CH2PX2 " have been compared with conformational stabilities obtained from temperature-dependent FT-IR spectra recorded in liquefied xenon solutions. Theoretical gas-phase proton affinities of arylphosphines have also been reported at the MP2 level. 

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