Hydrogenphosphinates

Hydrogenphosphinic acids (384) have been esterified with orthosilicate in excellent yields. Phosphinylidene acids react selectively under the same conditions (Scheme 101). One-pot procedures have been also described for the preparation of phosphinate esters from alcohols. ... 

Nitroalkyl Acids. - Additions of hydrogenphosphinic esters, Ph(R0)P(0)H, or diethyl (lithiodifluoromethyl)phosphonate to nitrostyrene or other nitroalkenes yield the nitroalkyl phosphonates (187) and (188), respectively. Diethyl (lithiodifluoromethyl)phosphonate also, by reaction with DMF, has provided (175), as already noted the condensation between the latter and nitromethane has given a 69% yield of (189) further reactions involving (175) (Scheme 12) have provided several additionally functionalized esters, amongst them (190). 

Several communications, summarized in Scheme 14, have described the synthesis of many amino-substituted dialkylphosphinic acids and phosphonic acids, and also many similarly substituted hydrogenphosphinic acids. Alkylation of the phosphinates (272) (R = H or Me, = Et, R = H) yields the corresponding (273) which, in a single step, are convertible into the useful intermediates (274). With 1,2-unsaturated nitriles, for example, the (3-aminopropyl)phosphinic acids... 

Within this area, the most recent developments in the synthesis of esters of phosphonic acids have been the direct alkylation of hydrogenphosphonates using diazoalkanes in the presence of copper-containing catalysts in benzene as the solvent Of those catalysts examined, the most effective seem to be [Cu(acac)2] and [Cu(OTf)2], with Cu, Pd and Rh acetates and [Ni(acac)2] being less effective. The overall reaction is that represented in equation 18, in which R and R may be H, Ph or a simple alkyl group, but they may also consist of a functionalized alkyl group in reactions catalysed by trifluoromethanesul-phonic acid A similar procedure has been applied to the hydrogenphosphinate Ph(MeO)P(0)H ... 

The alkylation of C-arylnitrones affords oximinium salts which also undergo addition reactions with hydrogenphosphonates or hydrogenphosphinates the products are O-alkylated derivatives of the hydroxy amino acids Although fairly complex... 

The key intermediate, a cyclic hydrogenphosphinate, 9,10-dihydro-9-oxa-lO-phosphaphenanthrene-lO-oxide, has been converted, originally by Japanese manufacturers, to a variety of difunctional polymer intermediates. Addition to itaconic ester produces a dicarboxylic ester commercially used to make thermoplastic polyesters. This technology is discussed below in connection with modified polyester fibers and epoxy resins. Addition of the hydrogen phosphonate to itaconic acid and copolyesterification can be done in a single operation (61). 

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