From Iminophosphoranes

In the reaction of iminophosphoranes (Et0)2P(0)CH2N=PPh3 5 with phenyl isocyanate, a 75 % yield of the expected carbodiimide 6 is obtained.  

Erom the iminophosphorane Ph3P=NCN and tertiary alkyl halides in the presence of antimony pentachloride the heterocumulene salts Ph3P=N+=C=NR SbCle (R = t-Bu or adamantyl) are obtained in excellent yields.  

The reaction of cyclic iminophosphoranes 7 with isocyanates produces a carbodiimide intermediate 8, which was characterized as the corresponding urea 9.  

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The smooth hydrolysis of imidoyl chlorides provides access to carbonam-ides from iminophosphoranes via an aza-Wittig reaction, without the occurrence of free acid or amino functions. This is of special advantage in the synthesis (Scheme 32) of sensitive substrates such as )8-lactam antibiotics (60) (77H719, 79JOC4393). 

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). 

The synthesis of iV-substituted-S -trimethylenepyrazoles (45) from iminophosphoranes and 2-azido-l-cyclopentene-l-carboxaldehyde has been described (R = Ph, CH2Ph, CH2C02Et) (88S742). 

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

A less usual type of 2-aza-l,3-butadienes is the class of C=C-conjugated carbodiimides like 3-59. They are readily available from iminophosphoranes and react smoothly with carbo- and hetero dienophiles to yield the desired heterocycles, e.g. 1,3-oxazine 3-60 (Fig. 3-18) [286-288]. 

The synthesis of N-substituted-3,4-trimethylenepyrazoles 67 from iminophosphoranes 66 and 2-azidocyclopentene-l-carbaldehyde has been described (Scheme 41) <1988S742>. 

Symmetrically substituted carbodiimides are also obtained from iminophosphoranes and carbon dioxide or carbon disulfide, involving isocyanates or isothiocyanates as intermediates. Instead of the heterocumulenes di-t-butylcarbonate is also used in the reaction with iminophosphoranes. For example, bis(l-naphthyl)carbodiimide is obtained in 64 % yield using this procedure. 

When carbodiimides are generated from iminophosphoranes with adjacent reactive groups, intramolecular cyclization occurs. For example, reaction of the bis-iminophosphorane 13 with two equivalents of isocyanate affords the tricyclic compound 14. ... 

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. 

An original synthesis of A -substituted-3,4-trimethylenepyrazoles (204) from iminophosphoranes... 

A useful synthesis of symmetrical diaryl carbodi-imides from iminophosphoranes (readily available from amines and triphenylphosphine) and carbon disulphide has been described (Scheme 50). ... 

Treatment of resin-bound iminophosphorane 197 with an excess of solid CO2 and CS2 in a sealed glass tube, and with aryl isocyanates afforded I-OXO-, 1-thioxo- 198, and l-arylimino-l//-pyrido[l,2-c]pyrimidine-3-car-boxylates 199 (OlJMClOll). Reaction of iminophosphorane 200, derived from 2-(2-azidophenyl)pyridine with excess PPh3, yielded 6//-pyrido[l,2-c] quinazoline-6-thione (201). 

The ready synthesis of iminophosphorane 767 from 766 and its subsequent conversion to benzylidene derivative 768 and aza-Wittig reaction... 

A general synthesis of the secondary amines RNHMe and RNHEt has been developed starting from the iminophosphoranes (181). Alkylation with methyl or ethyl iodides (all other halides gave olefins) gave the salts (182) from which secondary amines were obtained on alkaline hydrolysis. 

The iminophosphoranes (181) with imide bromides gave the amidino-phosphonium bromides (183) which, it appears from their temperature-variable n.m.r. spectra, are interesting fluxional molecules. The free energy of activation for the interconversion of (183a) and (183b) (R R = Pr R3 = Ph) is 17.2 0.9kcalmol-i. 

Oxazoles (191) are producedwhen triphenylphosphine is treated simultaneously with an a-azidocarbonyl compound and an acyl halide. The intermediate iminophosphoranes (189) react with the acyl halide before they can react with themselves to give pyrazines. Elimination of phosphine oxide from the resulting salts may give the intermediate halo-genoimines (190), or the oxazoles may be formed via the betaines (192). 

For the formation of iminophosphoranes from triphenylphosphine and a-bromo-ct-cyano-succinimides see Chapter 1, Section 2C. 

The 2,3-dihydro-6/7-pyrimido[2,l-A]quinazolin-4(177)-ones 201 were obtained in a one-pot synthesis from the iminophosphorane 199 and isocyanate, through the 2-aminoquinazoline 200. Yields were good (R1 = H, Rz = c-hexyl) to excellent (R1 = Rz = Ph) (Equation 21) <1996TL9071>. 

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... 

An efficient solid-phase synthesis of [l,2,4]triazolo[l,5-7]indazoles has been described starting from bis(azide) 367. The coupling of this compound with polymer-bound triphenylphosphine gives compound 368. This unprecedented bis(iminophosphorane) reacts with various isothiacyanates to give the corresponding iminophosphoranes 215 (unreported yields) attached to the resin (Scheme 37) <2000SL1411>. 

The reaction of the lithium compound 55, accessible from the iminophosphorane CH2(SiMe3)PPh2=NSiMe3 and BuLi, with PbCl2 gives colorless crystals of the lead complex 56 in 50% yield (Equation (21)).77 Similarly, treatment of PbCl2 with the lithium compound 57 affords yellow crystals of the donor-stabilized lead(ll) diaryl 58 in 70% yield (Equation (22)).78... 

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