Transition-Metal-Free and Visible-Light-Mediated Desulfonylation and Dehalogenation Reactions: Hantzsch Ester Anion as Electron and Hydrogen Atom Donor

Abstract

Novel approaches for N-and O-desulfonylation under room temperature (rt) and transition-metal-free conditions have been developed. The first methodology involves the transformation of a variety of N-sulfonyl heterocycles and phenyl benzenesulfonates to the corresponding desulfonylated products in good to excellent yields using only KO t Bu in dimethyl sulfoxide (DMSO) at rt. Alternately, a visible light method has been used for deprotection of N-methyl-N-arylsulfonamides with Hantzsch ester (HE) anion serving as the visible-light-absorbing reagent and electron and hydrogen atom donor to promote the desulfonylation reaction. The HE anion can be easily prepared in situ by reaction of the corresponding HE with KO t Bu in DMSO at rt. Both protocols were further explored in terms of synthetic scope as well as mechanistic aspects to rationalize key features of desulfonylation processes. Furthermore, the HE anion induces reductive dehalogenation reaction of aryl halides under visible light irradiation.

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

“…The fact that step 4 is an equilibrium indicates that dHE has not yet been formed on the hundreds of microseconds time scales and likely represents the rate-determining step in the catalytic cycle. The irreversible dehydrogenation of HE • to produce the more stableby about 30 kcal mol –1 dHE could not be fully elucidated from experimental data and might indeed involve multiple and competitive reaction pathways. − For instance, HAT from HE • to 2a • is more favorable compared to HE due to the subsequent aromatization of the pyridine ring forming dHE. However, such a pathway would have produced nearly equimolar concentrations of 2b and dHE .…”

Domino Ring‐Opening of N‐Tosyl Vinylaziridines Triggered by Aryne Diels‐Alder Reaction

“…These results greatly enriched the good synthetic potential of this method by N ‐detosylation and protection of sulfamides. In addition, the product 3 aa in the presence of Hantzsch ester and potassium tert ‐butoxide gave the desired product 11 in 95% yield [19] …”

Advantage of Using NaH2PO2 over Alkali Metal Formates as a Hydrogen Source for Pd‐gC3N4 Catalyzed Hydro‐Dehalogenation of Aryl Halides

“…[5,6] These kinds of reactions are eco-friendly and environmentally sustainable process. [7][8][9] M. Yus et al reviewed various types of metal-mediated hydro-dehalogenation systems in detail. [10] The catalytic hydro-dehalogenation process is also accompanied by reductive coupling reaction during the process.…”