Eosin Y as a direct HAT photocatalyst for the synthesis of tetrahydrodipyrazolopyridines under white LED irradiation

A facile and efficient synthetic protocol has been developed for the synthesis of biologically privileged tetrahydrodipyrazolopyridines via visible light mediated one pot pseudo-six component reaction of ethyl acetoacetate, hydrazine hydrate, multifarious aldehydes and ammonium acetate (Knoevenagel condensation-Michael addition) by using metal-free, inexpensive eosin Y organic dye as a direct hydrogen atom transfer (HAT) catalyst at room temperature in open air condition. Mild condition, good yields, environment-friendly, high atom economy and good functional group tolerance of an extensive range of both electron-withdrawing and electron-donating groups are extra features of this approach. Additionally, this methodology is also appropriate for multi-gram scale, which enlighten the potentiality of using this reaction for industrial purposes.