New methods in organophosphorus chemistry: a wide reaching tool box for the modern chemist

Phosphines have number useful properties most notably its nucleophilicity and high oxophilicity which allows it to be an effective activator and reducing agent of oxygen containing compounds such as alcohols and carbonyls. These properties allow phosphine to participate in a number of widely used reactions such as the Wittig, Appel, Mitsunobu and Staudinger reactions. DMAP on the other hand has been used as an effective acylation catalyst and has been incorporated in to the widely utilised Steglich esterification. This thesis details the development of a new three component reagent system consisting of PPh3, I2 and DMAP. This new system takes advantage of both the initial activation properties of Ph3P-I2 adduct formed from the combination of phosphine and iodine, as well as the nucleophilic catalytic properties of DMAP. This was initially developed as a new method for the direct coupling of carboxylic acids with alcohols and amines. For this purpose the new reagent system was highly successful resulting in good-excellent yields of both esters and amides in an extremely rapid reaction. The mechanism of this acylation process consists of two distinct stages; the first involves initial activation of the carboxylic acid the second a DMAP catalytic cycle. This led to the development of a catalytic system in terms of the DMAP but still offered significantly faster reaction times compared to other common mild reaction condition methods. The reagent system was also applied to the activation and further reactivity of oximes with the intramolecular cyclisation of 2-hydroxy-benzaldehyde oximes resulting in rapid formation of the corresponding 1,2-benzisoxazoles. The activation of oximes also led to the formation of novel DMAP-hydrazones which could undergo further reactivity with methoxide anion to form imidates. Benzaldehyde oxime did not produce a stable DMAP-hydrazone and instead undergo elimination reaction straight to the benzonitrile. Finally, the reagent system was applied to the formation of phosphazenes. This produced a range of aryl-phosphazene in high yields and fast reaction times. A one-pot urea system was then developed producing both asymmetrical and symmetrical ureas in good yield and under mild reaction conditions.