Studies on the generation of chemical diversity using hetero Diels Alder reactions and polyfunctional scaffolds
In the first part of this work we developed four novel methodologies for the generation of nitroso dienophile from commercially available hydroxamic acid I which is trapped with appropriate diene through a hetero-Diels-Alder (HDA) reaction (Scheme 1). These procedures afforded cycloadduct in good yields, employing reagents in a 1:1 ratio and only 5 mol.% catalyst loading. Remarkably, the crude reaction mixture showed the HDA adduct as the only compound present: this renders the reactions described herein as ideal for the development of tandem processes. Moreover, we demonstrated that these new methodologies can be applied to a large number of dienes.
In the second part we demonstrated the synthetic usefulness of styrylisoxazole IV which was used to access a number of compounds. Herein we describe the syntheses of aziridines V, N-Michael adducts VI, VII and VIII and S-Michael adducts IX which were obtained by reacting styrylisoxazole IV, with the corresponding nucleophile (Scheme 2).
We also report the one-pot preparation of S-Michael adducts IX from commercially available isoxazole X, an aromatic aldehyde XI and benzyl mercaptan XII (Scheme 3).