Diphenylphosphoryl azide conversions

Diphenylphosphoryl azide also gives good conversion of primary alkyl and secondary benzylic alcohols to azides in the presence of the strong organic base diazabicyc-loundecane (DBU). These reactions proceed by O-phosphorylation followed by Sw2 displacement.78... 

Three new synthetic methods for the conversion of alcohols into azides (and hence potentially into amines) have been published. One route involves a further application of the chemistry of 2-alkoxypyridinium salts (formed in situ from an alcohol and the 2-fluoropyridinium salt) in their reaction with azide ion " (Scheme 17). Another extends the utility of the triphenylphosphine-ethyl diazodicarboxylate system, using diphenylphosphoryl azide as azide donor (Scheme 18), but is sensitive to steric hindrance at the alcohol carbon. The third route (Scheme 19) achieves oxygen activation through the alkoxyphosphonium salts (39), which are prepared from the alcohol, a phosphine, and a positive halogen donor such as carbon tetrachloride (with primary alcohols) or Af-chlorodi-isopropylamine (in... 

The reaction of carboxylic acids with diphenylphosphoryl azide (DPPA) and subsequent Curtins rearrangement can be used for the conversion of malonic esters 304 into protected (/ )-2-methylcysteine 308. Monomethylation of dimethyl malonate followed by alkylation with t-butylchloromethyl sulfide gives the achiral diester 305. Enantioselec-... 

Carboxylic acids can also be activated by formation of mixed anhydrides with various phosphoric acid derivatives. Diphenylphosphoryl azide, for example, is an effective reagent for conversion of amines to amides. The postulated mechanism involves formation of the acyl azide as a reactive intermediate. 

The monoacid pentaester 6 is a versatile intermediate, nearly perfect for the synthesis of a series of compounds like tiiose above described. However, its synthesis (14) largely accounts for the low yield observed in the preparation of Ic. Furthermore, the conversion of methyl deoxycholate into the corresponding 3/ -NH2 derivative 14 (see Figure 5 Research route) involves the intermediate production of the SjS-Ns derivative 15. Although the latter proved a perfectly safe compound, we must underline that i) the reagent (Le. diphenylphosphoryl azide) which is used in the Mitsunobu reaction is extremely expensive ii) alternative approaches to generate the azide by phase tiansfer catalysed... 

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