The 1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides in Water Media

The 1,3-dipolar cycloadditions (DCs) of nitrile oxides (NOs) have been used as a powerful tool in synthetic organic chemistry. The cycloadducts arising from cycloadditions (CAs) of NOs to alkenes and alkynes (2-isoxazolines and isoxazoles respectively) are valuable synthetic intermediates because, among others, their capacity to mask other functionalities including alpha, beta-unsaturated ketones, beta-hydroxy carbonyl compounds and 1,3aminoalcohols. In particular, the beta-hydroxy ketone functionality is an illustrative example, making the NOs alkenes CAs reactions a synthetically equivalent methodology of aldol reactions. The vast majority of these reactions are carried out in organic solvents. Nevertheless, the use of water as an alternative solvent has evident advantages on the "Green Chemistry" concept. The critical discussion on the use of water instead of "conventional" solvents in the 1,3-DCs reactions of NOs is the objective of the present review.