Phosphoranes, reduction

A full account has appeared of the reactions of the ester phosphoranes (30 R = H) with acyl chlorides. Equimolecular proportions gave the salts (31) from which /8-ketoesters were obtained on electrolytic reduction. A 2 1 excess of phosphorane gave the allenic esters (32), presumably via the betaines (33). 

One of the reported syntheses of ( )-9-oxodec-2-enoic acid 392, the queen substance of the honey bee Apis mellifera, uses two ylide reactions 222). Starting from pimelic acid 385 the resonance-stabilized ylide 386 is prepared by alkylation of methylene-triphenylphosphorane 209 and the former hydrolyzed to 7-oxooctanoic acid 387. Reduction of the corresponding thiol ester 389 and olefination of the resulting aldehyde 390 with phosphorane 67 gives the ( )-2-unsaturated ester 391. The latter was hydrolyzed to pheromone 392 222) (Scheme 69). 

Hydroxydec-2-enoic acid 397 was identified in the fodder juice of the Weisel cells (gelee royale) of honey bees. One of the synthesis of 397 starts from suberic acid ethylester 393 222) which was first converted into the hydroxyacid 394 and then into the thiol ester 395. Raney nickel reduction of the latter yields an intermediate aldehyde which, in statu nascendi, reacts with the phosphorane 67 to give 396. Subsequent hydrolysis of396affords the ( )-a,0-unsaturated hydroxy acid 397 222) (Scheme 70). 

Other known methods for preparing O-alkyl enol ethers include, most notably, alcohol elimination from acetals, double bond isomeri2ation in allylic ethers, reduction of alkoxy enol phosphates, and phosphorane-based condensation approaches.5 These methods, however, suffer from poor stereoselectivity, low yields, or lack of generality, if not a combination of these drawbacks. 

---