Transition-Metal-Free Dehydrogenation of Benzyl Alcohol for C–C and C–N Bond Formation for the Synthesis of Pyrazolo[3,4-b]pyridine and Pyrazoline Derivatives

Abstract

A series of cascade reactions that produce a range of functionalized aromatic heterocyclic compounds with pyrazole/pyrazoline cores have been developed. The method relies on a metal-free dehydrogenative process to produce in-situ benzaldehydes. The produced benzaldehyde was then allowed to react with some other substances, including acetophenone, pyrazole amine, and phenylhydrazine. The intermediate produced from these substrates underwent several chemical processes, including electrocyclization, the aza-Diels–Alder reaction, and the formation of intramolecular C–N bonds. These positive outcomes would open up the possibility of producing biologically active pyrazolo­[3,4-b]­pyridine and pyrazoline derivatives through a variety of possible reactions.

Transition Metal Catalyst Free and Single‐Step Synthesis of Significant Thiosemicarbazones via Oxidative Coupling Strategy

“…[28,29] A plausible pathway for generating TSCs (Scheme 4) was deduced from the results of control test and previous research report. [26] Benzyl alcohol 1 a was converted into its potassium salt I by reaction with potassium tert-butoxide and then oxidized in air forming the potassium benzyloxy hydroperoxide intermeditae III. III generated benzaldehyde 1 a' by discharging potassium hydroperoxide.…”

“…Subsequently, Yu and co- workers reported the t BuOK-mediated acceptorless dehydrogenation of N-heterocyclic compounds. [26,27] Transition metal-free and base catalyst-mediated construction of TSCs from alcohols is still not explored. In contemplating this, we have investigated a metal-free methodology to synthesize highly important TSCs utilizing base catalysts through the dehydrogenative coupling of alcohols and substituted thiosemicarbazides.…”