Unsaturated carboxylic acids, reactions with phosphites

Attack on Unsaturated Carbon. The annual addition of phosphites to every variety of activated double bond continues. These include nitro-alkenes,9 a/S-unsaturated carboxylic acid derivatives,10 maleimides,11 fulvenes,12 and pyridinium salts.13 The reaction of diethyl phosphite with keten 0,N-, S,N, and Al,AT-acetals has been used to prepare the enamine phosphonates (19).14... 

With halogens, triaryl phosphites form phosphoranes which may dissociate into various aryloxy-phosphonium compounds. On the other hand, trialkyl phosphites undergo an Arbusov-type reaction with halogens (except F) at low temperature (6.349). Saturated carboxylic acids produce dialkyl phosphites (dialkyl esters of phosphonic acids), while unsaturated acids give dialkyl phosphonates (6.350, 6.351) and a-diketones give pentaoxyphosphoranes (6.344) above. Diphosphonates can be obtained from trialkyl phosphites (6.747). 

A new synthesis of a)S-unsaturated acids has been developed through alkylation of dibenzyl phosphite anion followed by carboxylation to give the phosphonate (11), which gives the olefin on reaction with aldehydes and two... 

Although the combined additive phosphonylation and esterification of an a,j5-unsatu-rated carboxylic acid by a trialkyl phosphite can thus easily, although not necessarily accurately, be envisaged, that of a similarly unsaturated ester, nitrile, or amide is perhaps not so readily apparent. Harvey showed that successful reaction between triethyl phosphite and such a substrate (Scheme 43) occurs in a protic medium. In this respect, the reactions proceed faster in methanol than in ethanol, but reactions are, in general, (including those of structurally analogous unsaturated ketones) much cleaner and faster when carried out in phenol, and also afford much higher yields in this solvent. It has also been shown that ammonium salts will also act as a proton source to allow completion of addition without alkylation. The later Russian workers used acetic acid with successful results ... 

Reaction of a,j5-unsaturated aldehydes with diethyl trimethylsilyl phosphite was used for the synthesis of chain-lengthened esters. Alkylation of the a-silyloxy-j ,y-unsaturated phosphonate with lithium diisopropylamide (Ida) and an alkyl halide occurs at the y-position with migration of the double bond to the a,j9-position. The silyloxyenolate could isolated in this reaction. Acide-catalysed alcoholysis leads to the carboxylic ester through the acylphosphonate (equation 93) ". ... 

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