Iminophosphoranes rearrangement

In a closely related system, cleavage of the AZMB-group with a proximal N-TCA group proved to be troublesome, due to iminophosphorane rearrangement Love, K. R. Seeberger, P. H. J. Org. Ghem., 2005, 70, 3168-3177. 

However, dicarboxylic acid dichlorides treated with iminophosphoranes (Scheme 116) show a substrate-dependent reaction. Thus, o-benzodiacetyl dichlorides (321) form chloroazepinones (322) only with A -arylimino-phosphoranes. N-Alkyliminophosphoranes, upon elimination of dichloro-triphenylphosphorane and subsequent Mumm rearrangement (71M168), give the cyclic imide (323) (90S149 91T53). 

Additionally, uracil 6-iminophosphorane, isocyanate, and o-methyl-e-caprolactim ether join to form the intensely yellow pyrimido[4 5 4,5] pyrimido[6,l-n]azepine (360), as shown in Scheme 130. Upon ring closure, methanol is spontaneously eliminated. Diethyl azodicarboxylate affords with the other components pyrimido[4,5-e][l,2,4]triazoline (361), which is closely related to the alkaloid isofervenuline. The imidazo[5, -/][ ,2,4]tria-zine (362) results in a known Michael-type rearrangement sequence by treatment with diethyl acetylenedicarboxylate (86JOC149, 86JOC2787) in this latter case, the Michael-type addition occurs much faster than the expected three-component reaction [93H(35)1055]. 

Very few 2/f-triazole syntheses involve azides, apart from those (such as 2-acetyl derivatives) which involve prior formation and rearrangement of IjEf-triazoles. Some vinyl diazides react with triphenyl-phosphine in mild conditions to give iminophosphoranes of 2-amino-triazoles (Scheme 36). ... 

Iminophosphoranes are obtained from (44) and ylides (Scheme 7) by a rearrangement that is influenced by substituents and the reaction temperature. ... 

Pentenenitriles and benzo[f]indoles. Ally iminophosphoranes are formed from the corresponding azides upon treatment with PPh j (Staudinger reaction). Condensation of these products with diaryl ketenes leads to 4-pentenenitriles by a sig-matropic rearrangement. In the homoallyl series the Wittig reaction is followed by an intramolecular Diels-Alder reaction. Mild dehydrogenation of the products gives ben zo[/] indoles. ... 

Ashfeld and coworkers proposed that the initial phosphinylation of oxime 2 and subsequent Staudinger-like reduction of the tosyl azide forms iminophosphorane 171 (Scheme 5.42k The formation of the phosphoryl bond upon rearrangement is a likely driving force behind the regioselective migration of the trans-oxime substituent (R in 171) to afford the nitriliumion 5. The corresponding anionic phosphoramide is released and then adds to the nitrilium ion amidine 17. A subsequent 1,3-phosphoryl shift leads to the final amidine product 173. 

A DFT study of the origins of stereoselectivity in the aldol reaction of bicyclic amino ketones (20) with aromatic aldehydes has been reported (Scheme 18). ° Base-catalysed direct aldolization of a-alkyl-a-hydroxy trialkyl phosphonoacetates with aldehydes proceeds via a fully substituted glycolate enolate intermediate formed by a [l,2]-phosphonate-phosphate rearrangement. High enantioselectivity can be achieved by the application of chiral iminophosphorane catalysts. 

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