Studies on O-alkylisoureas in solution phase and on solid support

Crosignani, Stefano (2003) Studies on O-alkylisoureas in solution phase and on solid support. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The use of polymer-supported reagents is proving to be an ideal methodology for the clean and efficient preparation of chemical libraries. Polymer-supported reagents for the oxidation of alcohols and for the O-alkylation of carboxylic acids were studied. Several polymer-supported sulfoxides were prepared in order to accomplish catch-and-release oxidations of primary and secondary alcohols. Unfortunately, an efficient protocol for the oxidations with purification of the intermediate polymer-supported sulfoxonium ion could not be achieved.

A protocol for the synthesis of polymer-supported O-alkylisoureas was developed, and the isoureas thus obtained proved to be excellent reagents for the O-alkylation of carboxylic acids. The usefulness of microwave irradiation to accelerate the esterification reactions was demonstrated. The use of polymer-supported isoureas as intermediates in a catch-and-release esterification procedure was also investigated.

Some novel reactions of O-alkylisoureas were investigated in solution phase. Alcohols could be O-benzylated using O-benzylisourea with Lewis acid catalysis. Isoureas were used as reactive intermediates for the cyclisations of β-hydroxyamides to form 2-oxazolines and of N-hydroxyalkylsulfonamides to form cyclic sulfonamides.

Finally, a new activation mechanism for the reactions of isoureas using acetyl halides has been discovered, and applied to an efficient one-pot conversion of alcohols into haloalkanes.

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