Organocatalytic Alkylation and Photoorganocatalyst-Free Acylation of Azomethine Imines by Hantzsch Esters under Blue LED Light

A synthetic method to prepare 1-alkyl-substituted-pyrazolidin-3-ones efficiently that relies on the 4CzPN-mediated alkylation of azomethine imines by 4-alkyl-substituted-1,4-dihydropyridines (DHPs) under blue light emitting diode (LED) light (λmax = 456 nm) is reported. An approach that exploits the ability of blue LED light to initiate the acylation of the imine substrate by 4-acyl-substituted-DHPs to give 1-acyl-substituted-pyrazolidin-3-ones is also presented. Achieved under mild reaction conditions at room temperature, the synthetic protocol was shown to tolerate a broad range of functional groups to afford the corresponding 1-substituted-pyrazolidin-3-ones in yields up to 99%.