Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1–3 with the Knoevenagel adducts 4–6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13–17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13–16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations.

The selective functionalization of 2-formylpyrrole to provide diverse 1,2- and 1,2,5-substituted pyrroles is described. These compounds were used as versatile building blocks in a divergent synthesis of biologically valuable aza-bycyclic skeletons, such as pyrrolizine and pyrrolizidine derivatives. These bicycles were prepared following metal-free cascade synthetic approaches via regioselective intramolecular 1,3-dipolar cycloadditions and stereoselective Knoevenagel/Michael/ cyclization­ with dimethyl malonate.

A simple green approach for the production of benzylideneaniline oxides is offered. This contribution was performed via the condensation of phenylhydroxylamine with several aryl aldehydes, in the absence of both catalyst and solvent, and using microwave irradiation as the activating reaction mode. In addition, good yields of the products were achieved in a short time. It is also worth noting that the work-up procedure is simple and the products do not require further purification. Finally, an interesting comparison without the use of microwave irradiation is also discussed.

A new approach is described for the synthesis of substituted indoles 5, through an intramolecular and regioselective Friedel-Crafts cyclization of enaminones 6a-h catalyzed by Lewis acids. Compounds 6 were prepared from the 2-anilinocarbonyl compounds 7, by treatment with DMFDMA under thermal or microwave (MW) irradiation conditions. An alternative and shorter one-pot two-step synthesis of indoles 5 was achieved starting from compounds 7 and promoted by MW radiation, including the elusive 2-acetylindoles 5i-m.