P-oxo ylide

Further, Wasserman and coworkers developed a direct acylation of stabilized phosphonium ylides by carboxylic acids in presence of the EDCI/DMAP (way c). This last method allows the introduction of a-aminoacid structures into the resulting P-oxo phosphorus ylides [19-25],opening the way to the total synthesis of depsipeptide elastase inhibitors [22,24] or cyclic peptidic protease inhibitor EurystatinA [20]. 

A new dipolarophile bearing a chirality-controlling heterocyclic auxiliary at the p-position is readily accessible from (5)-A -benzylvalinol and methyl ( )-4-oxo-2-propenoate. However, the dipolarophile is available only as an 86 14 equilibrium mixture of trans and cis stereoisomers (Scheme 11.20) (84). When this is used without separation in the reaction with the Al-hthiated azomethine ylide derived from methyl (benzylideneamino)acetate in THE at 78 °C for 3.5 h, a mixture of two diastereomeric cycloadducts (75 25) was obtained in 82% yield. These two cycloadducts are derived from the trans and cis isomers of acceptor, indicating that both cycloadditions were highly diastereoselective. 

In contrast, ethyl 3-oxo-4-(triphenylphosphoranylidene)butyrate behaves as a C,0-bis(nucleophile) when reacted with unsaturated 5(4//)-oxazolones 584 with a leaving group at the exocyclic p-carbon. In this case, initial Michael reaction generates 585 that eliminates HX to produce a resonance stabihzed ylide 586. Cyclization of 586 with ring opening leads to the interesting ylide intermediate 587 used for the synthesis of 2//-pyran-2-ones (Scheme 7.185). 

Reaction of dialkyl arylphosphonites or dialkyl alkylphosphonites with two molar equivalents of dimethyl acetylenedicarboxylate, through an analogous pathway to the reaction of trimethyl phosphate with the acetylenedicarboxylate, proceeds smoothly for 30 min at -70 °C to give phosphorus ylide 7 initially in almost quantitative yield. The ylide (31P NMR p 69.8 ppm) converts to affords the X5-phosphole 8, and then to cyclic ylide 9. Addition reaction of hydrogen bromide to the X5 -phosphole 8 at -70 °C occurs for dealkylation of the X5-phosphole giving the oxo-phosphole 10 (8p 38.7 ppm) (Scheme 2) [3]. 

The reaction of optically active (l-diethoxyphosphoryl)vinyl p-tolyl sulfoxide (20) with sulfur ylides has provided the corresponding cyclopropanes (21) in high yields (g) (Scheme 10).52,53 With fully deuterated dimethyl(oxo)sulfonium methylide, (CD3)2 S(0)CD2, the cyclopropanation reaction occurred in a highly diastereoselective... 

Canthaxanthine (53) is to be regarded as an oxidative metabolite of P-carotene (1). In its industrial production, 4,4 -diacetoxy-p-carotene (52) is used as a starting compound, being hydrolyzed and oxidized 51). This compound, in turn, is obtained by the dimerization of 4-acetoxy-retinal or its phosphorus ylide (51), according to one of the methods described above48. The reaction of 4-oxo-Cls-phosphonium salt (54) with C10 dialdehyde (22) likewise leads to canthaxanthine (53)48b). In a further production process, P-carotene (1) is directly oxidized with chlorate, under catalysis with iodine 49). 

As one might expect, the addition of carbanions to the ylide (34) results in addition to the iminium bond. Similarly, this bond is reduced to form the diazetidinone (35), which displays some interesting chemistry, such as ring-expansion to an oxadiazine upon treatment with acetic anhydride.Conversion of the ylide into 3-oxo-1,2-diazetidinium tosylate (36) is achieved by using toluene-p-sulphonic acid. Treating the tosylate with a 1,3-dicarbonyl compound provides a novel route to pyrazoles. ... 

The other approach to P-ylides based on the nucleophilic addition of phosphorus(HI) reagents to the terminal carbon atom of 1,2-diaza-1,3-butadienes has continued to find application. The reaction with dialkyl-phosphonites or phosphorus(III) amides under solvent-free conditions (and in the presence of atmospheric moisture) was found to be a convenient approach to a-phosphanylidene hydrazones (42). The linear ylides (42) in THF solution undergo further intramolecular transformations to give 1,2,3X -diazaphospholes (43) in the case of phenylphosphinite as a starting substrate or 5-oxo-4-phosphoranyidene-4,5-dihydro-l/f-pyrazoles (44) using tris(dialkylamino)phosphine. 

---