J Alkylation of 2-Hydrophosphinic Acids and Esters with Oxonium Salts

1) Method J Alkylation of 2-Hydrophosphinic Acids and Esters with Oxonium Salts 

According to Teichmann, Jathowski and Hilgetag the P = O group can be alkylated to the P-0—R group. Similarly, Hettche found that the cyclic 2-hydro- 

This reaction can also be used to convert the phosphine oxide 158. (Method I, p. 86) to 1-aiyl-l-alkoxy-X -phosphorin 156 

l-bis-dimethylamino-2.4.6-triphenyl-X -phosphorin 164 is allowed to react with 2 moles of trifluoroacetic acid and a 10-fold molar excess of methanol in refluxing benzene, one of the amino groups is displaced and 1-methoxy-l-dimethyl-amino-2.4.6-triphenyl-X -phosphorin 757 can be isolated in good yield. The phos-phonium salt 165 (H can also attack C-2) is initially formed by protonation of 164 at C-4 (or C-2). Nucleophilic substitution then leads to 167 via 166 (Hettche, ). 

Such nucleophilic substitutions can also be carried out on analogous 1,1-di-arylamino-X -phosphorins and on oxy-bis -X -phosphorinsii4 or acetates 153, the latter can be viewed as mixed anhydrides in which phosphinic acid or acetic acid are easily displaced by nucleophiles. These reactions have a broad application in synthesis. 

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