Pseudo-Wittig reaction

In molecular chemistry, ketones react cleanly with alkyhdene ligands via a pseudo-Wittig reaction. This reaction yields a metalloxo complex and an... 

Scheme 8 Pseudo-Wittig reaction between 17 and acetone...

Scheme 6.15 Proposed formation of the alkylidene oxo species from dioxo species via a pseudo-Wittig reaction.

Pseudo-Wittig reactions are also observed with metal carbonyl complexes. For example, reaction of W(CO)e with hexaphenylcarbodiphosphorane affords the metal cumulene 36 with elimination of PhsPO . 

Two mechanistic variations can be envisioned to be operative in some Wittig reactions. In some cases (Z-stereoselective reactions) a very asynchronous reaction with a 2-center "anti" pseudo betaine transition state is involved. The other mechanism involves a more synchronous concerted reaction with a 4-center "syn" transition state. These two mechanisms may compete, e.g., in the reactions of semistabilized ylides with aldehydes where mixtures of Z- and E-alkenes are obtained. Further details of these studies will be provided in future publications, as well as additional data about solvent effects. 

J. M. Garcia Fernandez, C. O. Mellet, V. M. Diaz Perez, J. Fuentes, J. Kovacs, and I. Pinter, Synthesis of (1 -6)-carbodiimide-tethered pseudo oligosaccharides via aza-Wittig reaction, Carbohydr. Res, 304 (1997) 261-270. 

The Wittig reaction can be modified to allow the synthesis of enamides. In Scheme 4.57, the Wittig olefination of A -formyl imide precursor III-85 [204] (pseudo-aldehyde) with a phosphonium ylide III-86 is shown. The A -formyl imide III-85 can be synthesized from the parent lactam unit. 

Corey s retrosynthetic concept (Scheme 9) is based on two key transformations a cationic cyclization and an intramolecular Diels-Alder (IMDA) reaction. Thus, cationic cychzation of diene 50 would give a precursor 49 for epf-pseudo-pteroxazole (48), which could be converted into 49 via nitration and oxazole formation. Compound 50 would be obtained by deamination of compound 51 and subsequent Wittig chain elongation. A stereocontroUed IMDA reaction of quinone imide 52 would dehver the decaline core of 51. IMDA precursor 52 should be accessible by amide couphng of diene acid 54 and aminophenol 53 followed by oxidative generation of the quinone imide 52 [28]. 

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