Phosphorus ylides, triazoles

An interesting application of a phosphorus ylide in heterocyclic synthesis is in a ring annulation. The diazopyrazole (592) when treated with various phosphorus ylides gave the 3//-pyrazolo[5,l-c][l,2,4]triazole derivatives (593) with elimination of triphenylphosphine (79TL1567). 

The diazopyrazole (93) with various phosphorus ylides afforded 3/7-pyrazolo[5,l-c]-1,2,4-triazoles (94) by elimination of triphenylphosphine (79TL1567). Reaction of 1-chloroisoquinoline with 5-phenyltetrazole gives 3-phenyl-1,2,4-triazolo[3,4-a]isoquinoline (96) via intermediate (95) (70CB1918) (cf conversion 86 — 87). 

The 1,7-electrocyclization of nitrile imines 47 has been proposed as a key step in the conversion of the stable phosphorus ylides 45 to pyrazolo[4,3-d] [2,3]benzodiazepines 48, upon refluxing in xylene (Scheme 16). Ringopening of the triazoles 45 and recyclization is postulated to give the pyra-zoles 46. Migration of the triphenylphosphine group, followed by the elimination of triphenylphosphine oxide, would then give the nitrile imine 47 (95TL5637). 

In substituted triazoles (obtained, for example, from phosphorus ylides and carbonyl-azides) H NMR is a valuable tool for determining the constituents and the progress of a reaction, as in the acyl group migration (34) (35) (70TL5225). In the case of the isomeric... 

Ethyl azidoformate reacts with a-keto and a-ester phosphorus ylides to give 1-carboethoxy-iiic-triazoles. ... 

L abbe and his collaborators have also demonstrated the importance of electronic effects in the synthesis of 1-vinyl-1,2,3-triazoles by adding azides ta either acetylenes (Eq. 15) or active methylene compounds (Eq. 16). In both cases iodoalkyl azides may be added, with comparable results, to produce precursors of 2.2-4 and 2.2-5. This very productive group has pioneered the excellent general method for l,5-disub tituted-l,2,3-triazoles involving phosphorus ylides (Eq. 17). The high yields and wide range of substituents employed makes this method most attractive. Product structures were demonstrated by the Dimroth addition and decarboxylation (Eq. 16). 

Sheehan and Robinson, using the method described in Chapters 1 and 2, prepared l,5-diphenyl-4-(2-aminoethyl)-l,2,3-triazole in good yield. L abb6 and his collaborators included one trisubstituted example in their study of a-keto phosphorus ylides (Eq. 18). ... 

The preparation of N-acyl-1,2,3-triazoles by reaction of N-trimethylsilyl derivatives with acetyl chloride has been reported by Birkofer and Wegner (Eq. 1). In a later paper they showed that the 1-N-product (5.1-1) is obtained at low temperature (15°), and the 2-N-product (5.1-2) at high temperature (120°). The yields are generally high (ca. 90%), and the isomer ratio for an unsymmetrical case was determined (Eq. 2). Zbiral and his collaborators have added acetyl azide to a-keto phosphorus ylides and have obtained generally good yields of N-acetyl-1,2,3-triazoles (Eq. 3). The isomer ratio for unsymmetrical products (5.1-3) was not determined. 

The presence of an acyl group characterizes the second most common disubstituted 1,2,3-triazole and in general may be obtained in excellent yield from, for example, aroyl azides and phosphorus ylides (Eq. 31). A similar reaction has been used to prepare an acetyl-1,2,3-triazolecarboxylic acid... 

Several D-ribofuranosyl [113] and L-arabinofuranosyl 1,2,3-triazole derivatives [114] such as 119 have been prepared by cycloaddition of the corresponding glycosyl azide to 2-ethoxycarbonyl-2-oxoethylidene-triphenylphos-phorane, followed by reaction with methanolic ammonia or primary or secondary amines (Scheme 29). Some of prepared nucleosides proved to be potent inhibitors of HIV-1 replication. Phosphorus ylides containing an a-oxo group in the chain behave in a similar way as activated acetylenes with electron-donating groups [108[. Presimiably the azide adds to the enolate form of the ylide, followed by elimination of PhsPO [108]. 

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