Phosphoranes, reaction with azide

Peptides. A new amide or peptide synthesis is based on the formation of iminophosphoranes, R N=PR3, from the reaction of azides with a tertiary phosphine. These phosphoranes react with carboxylic acids to form amides.1 Ethyl diphenylphosphinite is more useful than a triarylphosphine because the by-product is hydrolyzed to diphenylphosphinic acid, which can be readily removed. The iminophosphorane 2, derived from 1 and ethyl azidoacetate, reacts with CboGly-L-Phe-OH to give optically pure 3 in 70% yield.2... 

The reaction of dienamines and sulfonyl azides provides a method for the synthesis of vinyldiazomethanes.233,431 Likewise, the pyrolysis of a fluo-rinated 1-benzyltriazoline over a nickel surface yields difluorodiazometh-ane.145 The formation of diazo compounds from the reaction of azides with alkylidene phosphoranes apparently originates from an intermediate triazoline compound (Scheme 145)408,411 412,415,441... 

The j8-azidoacrylester 31 was obtained by a corresponding reaction sequence and also on direct treatment of the phosphorane with acetyl azide. Unfortunately, a number of other phosphoranes treated with either acetyl azide or acetyl chloride and sodium azide cyclized to 4-,5-iV-acetyl-l, 2,3-triazoles... 

The fact that tetrazolo[l,5- ]pyridine reacts with phosphines - via ring opening to the valence bond isomer azide -to give a phosphorane has been long recognized. Some novel applications of this transformation have been published during the recent period. The fused tetrazoles subjected to this reaction, the resulting phosphoranes, and the literature sources are summarized in Table 4. 

In another approach, 2-(alkylamino)alcohol is employed as starting material for aziridine syntheses with the aid of dihalogenophosphoranes (70BCJ1185). Intramolecular transformation of 3-azidopropyloxirane 73 results in a simultaneous formation of a condensed aziridino[l,2-a]pyrrol-idine system (Scheme 39). The azide group is first transformed into imino-phosphorane 74, the nucleophilic N atom cleaves the oxirane to form betaine 75 [as in the Mitsunobu reaction (81S1)], and the phosphorus is shifted from N to O and then eliminated as phosphane oxide under simultaneous cyclization to bicyclic 76 (89JA7500). 

Isocyanates have provided one carbon atom in transformations of the general type (296) - (290). Thus, azide (343) reacts with triphenylphosphine in a Staudinger reaction giving phosphorane (344) which is then treated with isocyanates (RNCO R = benzyl or aryl) giving naphthyridines (346) (50-59% yield) via the carbodiimide (345). The cyclization (345)->(346) occurred in toluene at 160°C (92T4601). Azide (347) undergoes a similar sequence of reactions yielding a 1 1 mixture of isomeric naphthyridines (348) and (349) (44—47% yield). 

Reactions of phenyl azide with a tautomeric mixture of (15) and (16) also lead to the phosphazenes (17) as intermediates, tentatively identified as such by n.m.r. spectroscopy. Intermediate (17) undergoes intramolecular addition of the N—H bond across the phosphazenyl linkage to form a phosphorane (18). Novel polymers (19), containing phosphazenyl side-groups, have been obtained by the azide route. 

It is sometimes desirable to avoid the use of alkoxide during the formation of C—C double bonds in the synthesis of / -lactams [3324]. An iminophosphorane (formed in situ from an azide and triphenylphosphine) reacts with a carboxylic ester group in a neighbouring malonylidene side-chain to form this ring [3792]. The classic Wittig reaction has been extended to the synthesis of 2-vinylindoles [3603], and other indoles have been obtained from isothiocyanato phosphoranes [3297]. 

A full account has appeared of the reactions of acyl azides with jS-keto-alkylidenephosphoranes. These phosphoranes with nitrile oxides gave isoxazoles (54) and the stable ylides (56) or (57), formed as shown via the quinquecovalent 1 1 adducts (55). ... 

Phosphoranylideneaminoquinones, e.g. (20), have been prepared in good to excellent yields by the reaction of phosphines with [2,l]benzisoxazole-4,7-quinones, e.g. (19)." A safer alternative to the vinyl azide-based synthesis of (N-vinylimino)phosphoranes (21) has been reported (Scheme 1)." N-(AlkyIthiomethyl)iminophosphoranes (23) have been synthesised from the benzotriazole-substituted iminophosphorane (22) and used without isolation to provide routes to N-alkylthiomethyl-imines, -amides, and -ureas. Tetraazolyl-substituted ylides (25) and (26) are the products of the reaction of vinylphosphonium salts (24) with excess sodium azide." The novel 1,2-1 -azaphosphete (28), which is potentially antiaromatic, has been prepared by the reaction of the azide... 

In 2012, Grushin s team developed a palladium-catalyzed carbonylative coupling of aryl iodides with sodium azide [103]. This catalytic reaction occurs smoothly at temperatures as low as 25-50 °C and 1 bar to cleanly produce aroyl azides from the corresponding aryl iodides, CO and NaNs (Scheme 4.52). The reaction exhibits high-functional group tolerance and can also be conveniently used for one-pot, two-step procedures furnishing primary benzamides, imino-phosphoranes, isocyanates, and ureas in high yield without isolation of the primary benzoyl azide product. 

The existing alternative preparative methods for the a diazo esters, such as diazotization of glycine esters, p3TolysIs of TYacylYVnltrosoglydne esters, hase-catalyzed cleavage of 0 dlazo ketoacetates, reactions of alkoxycarhonylmethylene phosphoranes with arenesulfonyl azides, or add catalyzed decomposition of acetic esters with aryltriazene substituents, all... 

Silylmethyl-Substituted Heterocumulenes. (Trimethylsilyl-methyl)iminotriphenylphosphorane is obtained from a one-pot reaction of the azide and triphenylphosphine (eq 3). The reactions of the phosphorane with carbon dioxide or carbon disulfide (eq 5) give trimethylsilylmethyl isocyanate or trimethylsilylmethyl isothiocyanate in 68 and 94% yields, respectively. ... 

---