Manganese(I)-CNP Complex-Catalyzed Multicomponent Synthesis of 2-Pyrazolines by Acceptorless Alcohol Dehydrogenation

Abstract

An efficient multicomponent cascade reaction for the synthesis of structurally diverse 2-pyrazolines has been developed through a Mn I -CNP complex-catalyzed acceptorless dehydrogenative coupling (ADC) strategy. The transformation integrates alcohol dehydrogenation, Aldol reaction, and subsequent cyclization with hydrazines in a single operation, enabling direct access to 2-pyrazolines from readily available alcohols, ketones, and hydrazines without the need for stoichiometric oxidants. A broad substrate scope was achieved, tolerating both alkyl and aryl substituents at the 3-and 5positions. Control experiments support that the Mn I catalyst operates exclusively in the initial alcohol-to-aldehyde dehydrogenation step, with the in situ generated α, β-unsaturated ketone serving as a key intermediate. This work provides a practical and sustainable entry to 2-pyrazolines and expands the synthetic utility of Mn I -catalyzed ADC chemistry.