Triphenylphosphine, reaction with organic azides

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... 

Modifications of C6 of CyD other than by tosylation are very rare. However, a single-step quantitative-yield synthesis of CyD monoaldehydes has been published. The CyD was dissolved in an organic solvent, Dess-Martin perodinane was added, and the mixture was stirred for 1 h at room temperature. Addition of acetone and cooling allowed isolation of the crude product by filtration [16]. Another synthesis was performed by using IBX (l-hydroxy-l,2-benziodoxol-3(lH)-one 1-oxide) as oxidant in DMSO. Mono-oxidation of jS-CyD was performed along with its incorporation into chitosan by a reductive coupling reaction [17]. A direct azidation of CyDs with sodium azide in the presence of triphenylphosphine-carbon tetrabromide has also been reported [18]. 

The alcohol group can be replaced by various nucleophilic entities (such as cyanide, azide, halide, etc.) by reaction with triphenylphosphine, diethyl azodicar boxylate, and either the conjugate acid (HX) or an organic derivative (R X) of the nucleophilic residue (equation 6). The reactions are found to proceed with inversion at the alcohol carbon, and mechanisms for these conversions have been discussed. 

Azides react with epoxides too. This epoxide is one diastereoisomer (trans) but racemic and the symbol ( ) under each structure reminds you of this (Chapter 14). Azide attacks at either end of the three-membered ring (the two ends are the same) to give the hydroxy-azide. The reaction is carried out in a mixture of water and an organic solvent with ammonium chloride as buffer to provide a proton for the intermediate. Triphenylphosphine in water is used for reduction to the primary amine. 

Esr studies wth organic spin traps have shown that azide radicals (N3) are formed in the reaction of hydroxyl radicals with azide ions, and that the radicals N 3 and OCN are formed by persulfate oxidations of azide and cyanide. However, azide radicals could not be detected in the photochemical reductive cis elimination of cw-diazidobis(triphenylphosphine)platinum(II) to give Pt(PPh3)2, even though they have been observed in the esr spectra of the photolysis products of other azido complexes. It is suggested, therefore, that the azide ligands are cleaved off as Ne (hexaazabenzene). Calculations have shown that Ne is slightly stabilized and could therefore be stable at the low temperatures of these experiments. 

---