Iminophosphoranes preparation

Molina, P., Alajarin, M., Lopez-Leonardo, C., Elguero, J. Four-membered heterocyclic rings from iminophosphoranes. Preparation and reactivity of 2,4-dimino-1,3-diazetidines and related compounds. J. Prakt. ChemJChem.-Ztg. 1993, 335, 305-315. 

Several interesting 1,2,4-triazole fused-ring systems have been reported. A facile synthesis of 3,5-dihydro-677-imidazo[l,2-fc]-l,2,4-triazol-6-ones 162 was obtained by an iminophosphorane-mediated annulation <06EJ04170>. 8-Trifluoromethyl-l,2,4-triazolo[4,3- >]pyridazines 163 has been prepared from 4-trifluoromethyl-4,5-dihydropyridazin-3-one... 

Crotyl diazoacetate has been prepared by the procedure described here and by the reaction of diazomethane with crotyl chloroformate. The lower homolog, allyl diazoacetate, has been )repared by the reaction of allyl glycinate with nitrous acid and by the successive conversion of allyl chloroacetate to the corresponding azide, iminophosphorane, and, finally, the diazo ester. ... 

Although several recent reviews deal with selected aza-Wittig reactions of iminophosphoranes (910PP1 92OPP209,92T1353 94S1197), heretofore no detailed synopsis has appeared on the preparative importance of this synthetic principle for individual heterocycles with different ring size. 

A variant of the Kirsanov reaction was developed by Zimmer et al, where the system iodine/base/triphenylphosphane was used for the preparation of iminophosphoranes (68TL3811). 

A recent review on four-membered heterocycles formed from imino-phosphoranes concentrates on the preparation and the reactivity of 2,4-diimino-l,3-diazetidine and related compounds (93JPR305). As an example, the synthesis via bisiminophosphorane 85 is described in Scheme 42. The bisiminophosphorane has both a heteroaryl and a styryl site. From a mechanistic view, the reaction of the bisiminophosphorane proceeds with aryl isocyanate formation via an aza-Wittig mechanism. Intermediate car-bodiimide formation (86) occurs directly on the iminophosphorane moiety... 

An easy one-pot procedure (Scheme 80) gives pyrimido[4,5-h]quinolines by reacting the iminophosphorane 215 prepared from o-azidobenzaldehyde with A(N-dialkylbarbituric acid (216). Refluxing in pyridine leads to the elimination of phosphane oxide and to quinoline 217 (92S827). 

Another general route to 5,10-dihydro[l,2,4]triazolo[5,l-b]quinazolines via the electrocyclization of an azino carbodiimide intermediate has been described (94S1057). The key iminophosphorane, a benzophenone-1-[(triphenylphosphoranylidene)amino]ethylidenehydrazone, was easily prepared in a Kirsanov-variant first applied by Bayless and Zimmer (68TL3811). It consists of the reaction of triphenylphosphine/iodine/trieth-ylamine with benzophenone 1-aminoethylidenehydrazone (94SI057). 

Molina et al. were able to prepare the mesoionic thiadiazole (292) from iminophosphorane 297 and carbon disulfide. As Scheme 106 shows, 298 reacts with a,w-dihalo compounds to form dimer 299 [91JCS(P1)1159]. The synthesis of the mesoionic thiazolo[2,3-6][l,3,4]thiadizole is described in (92T1285). 

Although this review is by no means exhaustive, it should present an impression of the importance of iminophosphoranes as versatile synthons in heterocyclic synthesis. Much attention was paid to the aza-Wittig reaction, which enables the preparation of a wide range of simple and complex heterocyclic systems. 

To examine further the possible intermediacy of iminoiodinane 101, a compound having this presumed structure was prepared (Scheme 17.33) [91]. Support for the assignment of 101 was obtained upon treatment with Ph3P, which leads rapidly to the formation of iminophosphorane 102. The putative iodinane 101 also reacts with 2 mol%... 

A phosphine-free procedure has now been developed that avoids the need to prepare the iminophosphoranes altogether. Thus, treatment of benzamidines 831 with aldehydes under microwave conditions results in direct formation of 4-substituted quinazolines 832 and benzoquinazolines <2005T3533>. 

Iminophosphoranes have also proved to be key intermediates because they react with carbonyl compounds, isocyanates, isothiocyanates, acid chlorides, carbon dioxide, and carbon disulfide to give a wide range of imines and heterocumulenes, which are intermediates to pteridines. The preparation of iminophosphoranes has been investigated... 

Singh and Lai [73IJC959 76IJC(B)685] prepared 8,9,10,11-tetrahydro-benzothiazolo[3,2-c]quinazolin-7-ium perchlorate (287) by dehydrative cyclization of 4-[(2-oxocyclohexyl)thio]quinazoline (286) with sulfuric acid and then perchloric acid. 2-(2-Azidophenyl)benzothiazole (288) reacted with triphenylphosphine to give the iminophosphorane, which cyclized to 289 on treatment with ethoxycarbonyl isocyanate (89T4263). 

Ten series of substituted iminophosphoranes (1-10) have been prepared, each series differing either in the steric or electronic effects of the phosphorus substituents. Within each series the N-aryl substituents, Y, (usually OMe, Me, H,... 

Imines have also been prepared by the reaction of iminophosphoranes with aromatic, heteroaromatic, aliphatic and a, 3-unsaturated aldehydes at reflux in dry benzene. Reactions with ketones were rather sluggish. Acetone was used as the reagent and the solvent and cyclohexanone was reacted at reflux in toluene for a prolonged period of time.235... 

A convenient synthesis of l//-indolyl-2-benzothiazoles in moderate yield by the direct conversion of indole-2- and 5-carboxylates with in situ generated trimethylaluminum-2-aminothiophenol was described. [95H1045] 2-Substituted 1,3-benzothiazoles having a variety of substituents can be prepared from 2-methylthio-N-triphenylphosphoranylideneaniline and acid chlorides by iminophosphorane-mediated cyclization. [95H455]... 

Diimino-l,3-diazetidines, preparation from iminophosphoranes and reactivity 93JPR305. 

The most common synthetic approaches to both types of pyrimidopyrimidine have been described in CHEC-I and in review articles by Delia . In addition some new strategies in the preparation of pyrimido[4,5-rf]pyrimidines have been developed in the last few years. A new approach is the aza-Wittig-type reaction of iminophosphoranes of 5-aminouracils with aromatic isocyanates which leads to functionalized pyrimido[4,5-rf]pyrimidines. Ethyl 1,3-dimethyl-6-(triphenylphosphoranylideneamino)-uracil-5-carboxylate (105) reacts with isocyanates via adduct (106a) intermediates to afford 7-ethoxypyrimido[4,5-. 

Bravo et al. treated (Ss)-(+)-p-toluenesulfinamide (63), prepared by hydrolysis of 44,23 with triphenylphosphine in the presence of DEAD to give the N-sulfinyl iminophosphorane 64 in 92% yield.45 The Staudinger, aza-Wittig reaction of 64 with methyl or ethyl trifluoropyruvate afforded the unstable sulfinimine 65. Attempts to purify the imino sulfinimines by flash chromatography resulted in hydrolysis. 

Preparation and reactions of iminophosphoranes and their synthetic applications in the aza-Wittig reaction... 

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