Sulfonylpyrazole- and pyrazole-directed ortho-selective C-H functionalization/alkenylation and desulfenylative olefination of aryl(sulfonyl)pyrazoles

ortho-Selective C-H alkenylation of arenes was achieved using sulfonylpyrazoles and pyrazoles as directing groups, favored by a combination of a Pd(OAc)2 catalyst, Boc-Sar-OH and silver acetate. A wide variety of mono-alkenylated products of aryl-sulfonylpyrazoles and pyrazoles were synthesized with complete site-selectivity under mild reaction conditions. This transformation tolerated several electron-withdrawing and electron-donating groups on the aryl ring and the yields ranged from 52% to 70%, producing highly decorated/valuable alkenylated sulfonylpyrazole and pyrazole derivatives. Amazingly, switching of the oxidant, with the use of AgBF4 in place of AgOAc, offered cinnamic acid derivatives through de-sulfonylation followed by alkenylation at the same position with good yields in the case of aryl-sulfonylpyrazoles. These kinds of molecules have great biological importance and target predictions indicate that they may serve as potential antifungal and anti-tumor agents.

Biomimetic design of an α-ketoacylphosphonium-based light-activated oxygenation auxiliary

The biomimetic design of a transition metal complex based on the iron(iv)-oxo porphyrin π-cation radical species in cytochrome P450 enzymes has been studied extensively. Herein, we translate the functions of this iron(iv)-oxo porphyrin π-cation radical species to an α-ketoacyl phosphonium species comprised of non-metal atoms and utilize it as a light-activated oxygenation auxiliary for ortho-selective oxygenation of anilines. Visible light irradiation converts the α-ketoacyl phosphonium species to the excited state, which acts as a transiently generated oxidant. The intramolecular nature of the process ensures high regioselectivity and chemoselectivity. The auxiliary is easily removable. A one-pot protocol is also described.

Brönsted acid-mediated annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines: efficient strategy for the synthesis of 1,3,5-trisubstituted pyrazoles

A diversity-oriented synthesis of 1H-pyrazole derivatives via Brönsted acid-promoted annulations of 1-cyanocyclopropane-1-carboxylates with arylhydrazines has been developed.

DMSO/I2 mediated C–C bond cleavage of α-ketoaldehydes followed by C–O bond formation: a metal-free approach for one-pot esterification

One-pot I₂/DMSO mediated metal-free C–C bond cleavage of aryl-/heteroaryl- or aliphatic α-ketoaldehydes offering a carboxylic acid followed by esterification is presented.