Phosphonate carbanions, reactions with nitrile

The preparation of a-selenoketones, esters, nitriles and related compounds can easily be performed via alkylation of the corresponding enolates or stabilized carbanions [21]. These compounds have found many synthetic applications in radical chemistry. In Eq. (9), a typical example involving a ketone is depicted [22]. The stability of a-selenoketones such as 41 is remarkable. Similar reactions with lactones have been performed. For instance, this approach has been applied to the stereoselective synthesis of oxygen-containing rings to either faces of a bicyclic structure [23]. The approach based on a-selenenylation/radical allyla-tion compares favorably with classical enolate allylation procedures, which usually leads to mixture of mono- and diallylated compounds. Furthermore, this strategy is excellent for the preparation of quaternary carbon centers [24] as shown by the conversion of 43 to 45, a key intermediate for the synthesis of fredericamycin A, [Eq. (10)] [25]. Similar reactions with sulfoxides [26] and phosphonates [27] have also been reported. 

A related process consists initially in the reaction between diethyl methylphosphonate carbanion and a nitrile, RCN, to give the species 318, and the alkylation (R = Me, CH2CH=CH2, CH2Ph) of the latter. Work-up of the product under basic conditions leads to the enamines 319. Work-up with acid conditions affords the (2-oxoalkyl)phosphonic diesters 320 the latter were also obtained through acidolysis (3 m H2SO4) of the enamines 319. A wide choice of alkylating species is possible alkyl halides, disulphides RSSR (R = Me or Ph), sulphenyl chlorides RSCl (R = Me or Ph), PhSeBr, MeS02SMe and PhSOoCl have all been used ". ... 

Phosphonate carbanions, formed by percolation of a dilute ether solution of the diethyl phos-phonate through a macroporous AER in HO" form, react with carbonyl compounds in Horner-Wittig syntheses of alkenes (Scheme 20). " a,j -Unsaturated nitriles are formed from both aldehydes and ketones, but a,) -unsaturated esters are formed only from aldehydes. The reactions... 

The factors affecting the competition between transesterification and olefination in reactions of phosphonoalkylcarboxylates (111) with aldehydes and potassium carbonate in alcohols under heterogeneous conditions have been investigated.57 The reaction of the carbanion of I-cyano-1-fluoromethanephosphonate, prepared in situ from diethyl cyanomethane-phosphonate (112) and N-fluorobis(trifluoromethanesulphonyl)imide, with aldehydes and ketones provides a synthesis of a-fluoro-a,3-unsaturated nitriles (113) in moderate yield (Scheme 8).5 Wadsworth-Emmons... 

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