Phosphorane ylid rearrangement

With cyclic phosphite 3, when the trapping reagent used in reaction is phenol, we obtain a quantitative yield of ylid. Between 0° and 20° this ylid undergoes a complete rearrangement leading to a phosphorane (J ) ... 

Conversely, a phosphorane is obtained at -20°C when the PIII reagent is trimethy 1phosphite and methanol is the trapping species. This phosphorane undergo a complete rearrangement in a few minutes at 20°C leading to an ylid. 

In table 1, the three phenomena which correspond to the paper s title are encircled. We can also see that the same reagent i.e.methanol always gives a phosphorane. This one is stable when the phosphite reagent is a cyclic species. This phosphorane then undergoes a rearrangement to an ylid when the phosphite reagent is a linear species (P(0Me)3). 

At low temperature, the ylid 4 adds methanol before giving by rearrangement a phosphorane 5 which finally lead to a saturated phosphorane 11. 

In an extension of earlier work, Buigada et al. have also reported on the reaction of the cyclic phosphite (66) with dimethylacetylene dicarboxylate (58) in the presence of proton sources such as carboxylic acids, amide N-H bonds in succinimide or phthalimide and amine N-H bonds in p UTole or indole. With carboxylic acids (67) a mixture of the ylid (68) and the cyclic phosphorane (69) was obtained and in some instances (e.g. with 2,4,6- trimethylbenzoic and p-methoxybenzoic acids) the ylid and phosphorane were shown to be in equilibrium. With amides as the proton source, ylids were generally formed although with N-methylbenzamide (PhCONHMe)a signal attributed to (70) was observed at = - 52 p.p.m. which had disappeared by the end of the reaction through rearrangement to (71). With amines (e.g. pyrrole) the products were again a mixture of ylid (72) and phosphorane (73) and the entire set of results was rationalised in terms of HSAB theory and the symbiotic effect around phosphorus. 

Methylenetriphenyl phosphorane has been used for the synthesis of a variety of cyclic compounds by a combination of ring closure and nucleophilic ylid reaction A new simple synthesis of isoflavones via a thallium(III) acetate-promoted rearrangement of chalcones has been published ... 

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