Polystyrene-bound triphenylphosphan

Another well-known process that utilizes a nucleophilic phosphane is the Mit-sunobu reaction, that is, the reaction between an acidic partner and an alcohol, typically facilitated by an azodicarboxylate and a phosphane. Two options are possible, anchoring of the electrophilic part to the solid support, dealt with in the next section, or anchoring of the nucleophilic phosphane. Georg et al. used polystyrene-bound triphenylphosphane and DEAD (diethyl azodicarboxylate) in their synthesis of aryl ethers [31]. Alcohols were reacted successfully with electron-rich and electron-deficient phenols, giving the desired products in good yield and purity. More recently, Wilhite and coworkers disclosed an efficient protocol for the synthesis of pyridine ethers using ADDP [l,l -(azodicarbonyl)dipiperidine] and polymer-supported triphenylphosphane (Scheme 6.9) [32], Both methods eliminate purification problems caused by triphenylphosphane oxide, but chromatography is still needed. 

Ley and coworkers used this method to carry out the cyclization of 1,4-disubstituted-(thio)semicarbazides, forming 2-amino-l,3,4-oxadiazoles (Scheme 6.6). A polymer-bound tertiary base was needed to facilitate the ring closure [16], In summary, the most obvious advantages of the CC14 or CBr4/PS-TPP (polystyrene-supported triphenylphosphane) system are the ease of purification... 

The combination of polystyrene-bound triphenylphosphine and carbon tetrachloride has been used for the condensation of N-alkoxycarbonyl a-amino acids and primary amines, including amino acid esters, in the presence of N-methyl-morpholine as base and refluxing dichloromethane as solvent [56]. In this case, supported triphenylphosphane oxide was isolated by filtration after the coupling reaction. The nature of the intermediate involved in the condensation was supposed to be the acid chloride, as these derivatives are found when heating polystyrene-supported dichlorotriphenylphosphorane with carboxylic acids [57, 58], However, evidence supported by infrared spectroscopy suggests the formation of... 

---