NH-Isoxazolo-bicycles; new molecular scaffolds for organocatalysis

A new scaffold for organocatalysis of the Diels–Alder reaction is disclosed; an isoxazolidine ring forms the core of the catalyst and its activity is enhanced by judicious fusion of a second five-membered heterocycle to the c-edge. The catalyst performance is improved by the incorporation of an endo-cyclic electron withdrawing group adjacent to the fusion point. The organic core is effective only in the presence of an acid co-catalyst and whilst the two-component system shows potential as an enantioselective catalyst it is demonstrated that stereocontrol is a feature of the organic core and is fully independent of the choice of co-catalyst.