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 5-positions. Control experiments show 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.