With iminophosphoranes

Imido-bromides yield amidinotriphenylphosphonium salts (73) with iminophosphoranes. The fluxional nature of these salts is shown by the marked temperature dependence of the n.m.r. of the alkyl groups. ... 

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). 

In some cases, side reactions were observed. When 4-chlorophenyl isocyanate reacted with iminophosphorane 135 (R= Pr ), along with the corresponding pteridin-4(377)-one (43%), the hydrolyzed compound, 3-isopropylpteridine-2,4-(177,377)-dione (26%), was also isolated. In cases with additional functional groups in the pteridine substrate such as esters, polycyclic compounds such as the imidazo[2,T ]pteridine derivative 138 (37%) were obtained. Similarly, Wallyl and W(l-methylprop-2-enyl) groups in 137 gave imidazo[2,l- ]pteridines 139 by iodoamination. 

Aziridines are obtained in one step from oxiranes with iminophosphoranes (76CB814) or phosphoramidate esters (76TL4003). 

Isothiocyanates are also major starting materials for carbodiimides either by converting them into 1,3-disubstituted thiourea intermediates, which are subsequently desulfurized, or by treating them with iminophosphoranes. 

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. 

Dicarbodiimides have not gained the same prominence as diisocyanates as monomers for addition polymers. Dicarbodiimides are obtained from difunctional precursors, such as bis-thioureas. Another synthetic method is the conversion of diisocyanates with iminophosphoranes. The reaction can be condncted stepwise to give an isocyanato-carbodiimide as an intermediate. 

The reaction of a-chloroisocyanates 3 with iminophosphoranes is a mild and efficient method of synthesis of o -halocarbodiimides 4 ... 

Also, in the reaction of the a-difluoro isocyanates 5 with iminophosphoranes Ph3P=NR (R = i-Pr, Ph, 2,4,6-Mc3Ph) the corresponding carbodiimides 6 are obtained in 40-60 % yield." ... 

Orthopalladated complex [Pd(/i-Gl)(G6H4-2-PPh2=NPh-/ -6 ,A)]2 and related complexes have been obtained by the reaction of Pd(OAc)2 with iminophosphoranes. ... 

Aryl imines are also prepared from JV-nitrosoamines by thermal elimination of from aldehydes by reaction with iminophosphoranes, from... 

The cycloaddition reaction of carbon dioxide across P=N bonds is likewise observed, but in these cases an exchange reaction occurs with formation of isocyanates. The [2+2] cycloaddition reaction of iminophosphoranes with carbon dioxide was already investigated by Staudinger and Hauser in 1921 . A mixture of isocyanates and carbodiimides was obtained, because the generated isocyanate 50 reacts with iminophosphoranes to give carbodiimides 51. 

The reaction of carbon disulfide with iminophosphoranes is quite general. In addition to trialkyl- and triaryliminophosphoranes also bisalkoxyalkyliminophosphoranes, trialkoxyiminophosphoranes , dimeric trichlorophosphazenes and phosphoramidate anions react similarly. Bisiminophosphoranes react with carbon disulfide to give diisothiocyanates which are used in the construction of macrocyclic carbodiimides". ... 

Route B is also versatile and efficient (/-/,/5), allowing for the preparation of iV-aryl, A -alkoxycarbonyl and also A -unsubstituted polyfluoroalkyl enamines and imines in good to excellent yields. Starting material in this case are fluorinated p-sulfmyl ketones 7, which were submitted to Staudmger (aza-PP/7%) reaction 16,17) with iminophosphoranes 8. Monofluorinated ketones 7 were found to be poorly reactive when submitted to the Staudinger reaction, therefore low yields (10-30%) of the corresponding products were generally obtained. No reaction was achieved with nonfluorinated 3-ketosulfoxides. 

Another total synthesis used the rich chemistry of iminophosphoranes (95AHC159). The /3-(3-indolyl)vinyl iminophosphorane 354 underwent an aza-Wittig/electrocyclic ring closure reaction to give the carboline 355 which was hydrolyzed with lithium hydroxide (Scheme 106). A selective reduction, deprotection, decarboxylation and diazotation followed by ring closure gave Fascaplysine (353) (94TL8851). 

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 conversion of an alcohol to an amine can be achieved in a one-pot reaction the alcohol 1 is treated with hydrazoic azid (HN3), excess triphenylphosphine and diethyl azodicarboxylate (DEAD). The initial Mitsunobu product, the azide 14, further reacts with excess triphenylphosphine to give an iminophosphorane 15. Subsequent hydrolytic cleavage of 15 yields the amine—e.g. as hydrochloride 16 ... 

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). 

A Wittig-type reaction of iminophosphorane 995 with benzoyl and ethoxycarbonyl isocyanates gave (91T6747) thiadiazolotriazines 996, whereas reaction of 995 with aromatic isocyanates afforded 997. On the other hand, iminophosphorane 995 reacted with methyl and benzyl isothiocyanates to give 998. Reaction of 995 with acid chlorides gave 999 (88H1935). All these compounds display mesoionic or zwitter ionic character (Scheme 184). 

Reaction of iminophosphorane 1006 with ethoxycarbonyl isocyanate gave (91T6747) regioselectively thiadiazolotriazine derivatives 1007, whereas treatment of 1006 with aromatic isocyanates in ethanol or in the presence of tetrafluoroboric acid afforded 1008 and 1009, respectively. Similarly, 1006 with methyl isocyanate gave 1010 (91T6747) (Scheme 187). 

Diphenylcarbodi-imide reacts with ylides to give, in general, the iminophosphorane (86) and the imines (85). The latter usually react with a second mole of ylide to give the stable phosphoranes (87) although the imine (85 R = R = Ph) was isolated. Hydrolysis of the solution... 

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). 

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