Iminophosphoranes, condensation with

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

Starting from acylated 2-azidomethylbenzimidazoles (145), an additional imidazole ring can be condensed by transformation of the azido group with tri-n-butylphosphane into the appropriate iminophosphorane intermediate 146. After extrusion of phosphane oxide, cyclization occurs to the 1-substituted 4//-imidazo[l,5-a]benzimidazole 147 (Scheme 58) (89T1823 94S1197). 

Several condensed systems, especially those combined with pyridine rings, show biological activity, e.g., in the field of crop protection and as anti-virus and anti-cancer compounds. Aza-Wittig reactions in particular should make several novel heterocyclic rings available. The aza-Wittig reaction of iminophosphoranes has to be considered as a major principle in modern synthetic chemistry, as was wisely foreseen by Staudinger and Meyer as early as 1919. 

A rather unusual nitrogen source for the pyridine moiety is the iminophosphorane function. Condensation of l,3-dimethyl-2,4-dioxo-6-[(triphenylphosphoranylidene)amino]-l,2,3,4-tetrahydropyrimidine with 7V,7V-dimethyl-/i-nitrovinylamine yields an iminophosphorane 27, which then in consecutive aza-Wittig and electrocyclization reactions with arylisocyanates gives the corresponding pyrido[2,3-rf]pyrimidines 28.186... 

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. ... 

A variety of cyclic phosphonium ylide structures have been reported. Hetero-cyclic and -bicyclic structures, including the ylide (11) and a variety of iminophosphoranes, are the products of the reaction of the 1,2-dihydro-1,3,2-diazaphosphinine (10) with dimethyl acetylenedicarboxylate. Attempts to prepare a simple adduct of DBN with the (phosphino)(P-chlorophosphonio) carbene (12) led instead to formation of the unsaturated tricyclic adduct (13). The diphosphete structure (14) is the product of a simple two component reaction of dichloro(bis(trimethylsilyl)methylphosphine) with DBU. Details of the synthesis, chemistry and structure of X -phosphetes (15), benzo-X, -phosphetes (16), and naphtho-X -phosphetes (17) have been reported. 2,4-Diphosphoniodihydro-phosphetide cations (19) have been prepared by condensation of the... 

The first bis(iminophosphorane (7.515e) was reported by Niecke and Flick in 1974 [13]. Condensation of (Me3Si)2NP=NSiMe3 with trimethylsilylazide first produces a complex, then above 100°C rapidly forms bis(trimethylsilylimino)phosphorane mp = 36°C, which reacts extremely rapidly with water. 

Under ruthenium-catalyzed ortho-C-H activation and intramolecular C-N bond formation, the condensation of iminophosphoranes (in situ generated from acyl azides and triphenylphosphine) with internal alkynes afforded a variety of isoquinolinone derivatives (Eq. (7.43)) [53]. The regioselective insertion of unsymmetrical alkynes led to an (aryl)C-N bond formation. Thiophene and indole-based acyl azides were also compatible for this transformation. A domino reaction sequence via coordination of ruthenium with Af-atom of iminophosphoranes, ort/zo-cyclometalation, alkyne insertion, protonation, and reductive elimination was proposed for the catalytic cycle. Based on and NMR experiments, the involvement of benzamide during the reaction process was ruled out. 

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