Azide with triphenylphosphine

Recently Zbiral and Stroh reported that treatment of a-azido-ketones (obtained generally by reaction of the a-halogenoketone with sodium azide) with triphenylphosphine is a convenient route to 2,5-disubstituted pyrazines (Scheme 5). Thus, 2,5-diphenyl-, 2,5-bis(4-methoxyphenyl)-, and 2,5-diisopropylpyrazine have been obtained in 75, 45, and 44% yield, respectively. The intermediate P-iV-ylide undergoes intermolecular condensation to give a 2,5-dihydropyrazine which is subsequently aromatized.122... 

By far the most common method of formation of IMPs is the Staudinger reaction.1 This is the reduction of an organic azide with triphenylphosphine (Scheme 4). It has been proven that attack of the phosphorus is at the terminal nitrogen of... 

Staudinger reduction Reduction of azides with triphenylphosphine. 428... 

The Staudinger reaction is a mild method for the conversion of azides to amines by treating the azide with triphenylphosphine in the presence of water. The water is necessary, because the intermediate iminophosphrane is hydrolyzed to form the amine and triphenylphosphine oxide. Reviews (a) Gololobov, Y. G. Kasukhin, L. E Tetrahedron 1992, 48, 1353-1406. (b) Gololobov, Y. G. Zinnurova. 1. N. Kasukhin, L. E Tetrahedron 1981, 37,437 72. 

Iminophosporanes (phosphazenes) are easily formed by a Staudinger reaction of azides with triphenylphosphine or a Kirsanov reaction, which is a process that takes place between an amine and dichlorotriphenylphosphorane. The ready availability of... 

The Wittig reaction of the to-azidoalkylidene ylides (249) with the aldehyde (250) has been used in a synthesis of Theonelladins (251) and (252). 50 The reaction of allylic azides with triphenylphosphine followed by treatment with the corresponding ketene provides a one-pot synthesis of a-allylated nitriles (253) in moderate yield. 5 ... 

Treatment of a-D-glucopyranosyl azide with triphenylphosphine in the presence of carbon dioxide afforded carbamates 26 and 27, in which the configuradon at C-3 is retained and inverted, respecdvely, as well as their a-D-fioanose isomers. Similar results were observed for a-D-xylopyranosyl azide, and a mechanism involving intramolecular displacement at C-3 was invoked to explain the inverted products. ... 

S,3S)-(+)-Aziridine-2,3-dicarboxylic acid (234 Scheme 3.86), an example of a naturally occurring aziridinecarboxylic acid, is a metabolite of Streptomyces MD398-A1. This aziridine was prepared by treatment of diethyl (2i ,3K)-(-)-oxir-ane-2,3-dicarboxylate (231) with trimethylsilyl azide in EtOH/DMF to produced azido alcohol 232 [137], and treatment of this alcohol with triphenylphosphine afforded the aziridine dicarboxylate 233 in 71 % yield. Hydrolysis of 233 afforded the natural product 234 in 69% yield. 

It may be concluded that the conversion of functionalized oxiranes into the corresponding aziridines by an azide ring opening followed by a Staudinger ring closure with triphenylphosphine constitutes a general method for the preparation of aziridines with high enantiopurity. 

The reduction of an azide group with triphenylphosphine in tetrahydrofuran by microwave heating at 130 °C for 5 min has been described by Kihlberg and colleagues (Scheme 6.152) [297]. The use of diethyl 4-(hydrazinosulfonyl)benzyl phosphonate as an in situ diazene precursor for the reduction of trisubstituted gem-diiodoalkenes to terminal geminal diodides under microwave conditions has also been reported [298],... 

Scheme 6.152 Reduction of an azide group with triphenylphosphine.

Synthesis of the amino-triazole derivative (43) was performed in the authors laboratory by Pati et al. [52] (Scheme 7). Substituted benzyl bromide was reacted with triphenylphosphine to produce the phosphonium bromide starting material, 44. The Wittig reagent, obtained by treatment with sodium hydride, was reacted with 3,4,5-trimethoxybenzaldehyde 18 to generate the nitro-stilbene 45 in good yields. The alkyne 46 was obtained by bromination of the stilbene, followed by didehydrobromination. Compound 46 was then reacted under thermal conditions with benzyl azides... 

V-Methyl-/V-(2-perlhioroalkyl)ethy I amines 17 (R = C4F9, QT n or C-xI i 7) were prepared from the azides 16 by sequential reaction with triphenylphosphine, methyl iodide and aqueous potassium hydroxide45. 

One of the classical methods for the synthesis of pyrazines involves dimerization of an a-amino carbonyl compound and subsequent aromatization. Cyclic dimerization of the a-amino ketone, which is formed by reduction of a-azido ketone 149 with triphenylphosphine, leads to the formation of a pyrazine derivative 150 (Scheme 40) <1994JOC6828>. Reduced Te also dimerized a-keto azide 149 to give pyrazine 150 <2006JOG2797>. 

An alternative approach to N-S bond formation involves the aza-Wittig-type reaction of sulfoxides (Scheme 26) <2004SL101>. Initial Staudinger ligation of aryl azide 195 with triphenylphosphine afforded iminophosphorane 196, which was purified by column chromatography and then heated in anhydrous toluene, producing benzothiazines 62 and 197. The N-S bond was found to be rather sensitive to hydrolysis and cleavage to 198 was observed upon treatment of benzothiazines 62 or 197 with wet THF. 

Vicinal diazides 85a-c, prepared by the action of sodium azide on the corresponding 3,4-dichloromaleimide, react with triphenylphosphine in refluxing dichloromethane to give 2-amino-l,2,3-triazole derivatives 86a-c (Scheme 9). The stable di-Staudinger side products 87a-c are also produced from the reaction <2005JCX385>. 

A one-pot cascade approach to 4-alkylidene-(3-lactams from aryl azides and aryloxyacetyl chlorides has been reported. (4-Methyloxyphenyl)azides reacted with triphenylphosphine in 1,2-dichloroethane to form triphenylphosphazene, which was treated with phenoxyacetyl chloride and Et3N to afford 4-phenoxy-methylene-(3-lactam (Scheme 45), [122]. 

---