Visible-light-mediated synthesis of β-keto sulfones using g-C3N4 as a recyclable photocatalyst under sustainable conditions

An inimitable illustration of blue-light-induced synthesis of beta-keto sulfones has been disclosed using commercially available phenylacetylenes or ketones as precursors and sodium sulfinates as the sulfonyl source. Here, the synthesized heterogeneous graphitic carbon nitride (g-C3N4) was employed as a recyclable photocatalyst. The mechanistic investigation revealed that the formation of beta-keto sulfones from phenylacetylenes proceeds via a beta-iodo sulfone intermediate. While for ketones, it proceeds via a radical C-I cleavage of the in situ generated alpha-iodo ketone intermediate, followed by the attack of the sulfonyl radical. Potent biologically active compounds like anti-analgesic agents and CES1 inhibitors were synthesized using the present protocol. To explore the applicability, a few post-synthetic modifications of beta-keto sulfones were also carried out. Finally, to show the greener aspects of the protocol, green chemistry metrics (mass efficiency, atom economy, atom efficiency, carbon efficiency, E-factor and eco-scale) of one of the derivatives of both phenyacetylens and acetophenones have been calculated. The E-factor of the current protocol was found to be 1.1 times (with phenylacetylene) and 1.2 times (with acetophenone) higher than that of a reported thermal process. The eco-scale value of the current procedure was also found to be acceptable (with both acetylene and acetophenone). Besides this, metal, base and ligand-free reaction conditions, a recyclable photocatalyst (up to five cycles) and wide substrate variability are some additional advantages of this methodology.

Automated summary

This study presents a method for the blue-light induced synthesis of beta-keto sulfones using commercially available compounds and a recyclable photocatalyst. Mechanistic investigation revealed different pathways for the formation of beta-keto sulfones from different reactants. The method also enabled the synthesis of biologically active compounds and post-synthetic modifications. Additionally, the method demonstrated good environmental friendliness and wide applicability with the absence of metal, base, and ligands.