Reagentless Chemistry "On-Water": An Atom-Efficient and "Green" Route to Cyclic and Acyclic β-Amino Sulfones via aza-Michael Addition Using Microwave Irradiation.

A reagentless, catalyst-free, and sustainable methodology was developed for facile access to cyclic and acyclic β-amino sulfones "on-water" using a microwave. A variety of aromatic and aliphatic amines undergo double aza-Michael addition on the surface of the water with water-insoluble divinyl sulfones upon microwave irradiation at 150 °C for 10 min to mostly afford solid cyclic β-amino sulfones as easily separable products in excellent yields by simple filtration avoiding any workup steps. Thus, all atoms of the substrates are reflected in the product making it a 100% atom-efficient method. Both electron-rich and electron-deficient amines participated well in the reaction as well as good functional group tolerance was observed. The competitive experiments expectedly revealed faster reaction kinetics for electron-rich amines. The methodology was extended to acyclic β-amino sulfones by interacting phenyl/ethyl vinyl sulfones with various amines in a similar manner. Expectedly, the method afforded very low environmental factors (in a range of 0.05-0.5) and a high Ecoscale score (up to 94). In an attempt toward sustainable development, this reagent-free, metal-free, organic solvent-free, cost-effective protocol is certainly a viable alternative to the available methods for β-amino sulfones.