Synthesis of dihydropyrano[2,3-c]pyrazole scaffolds by methylene blue (MB+) as a photo-redox catalyst via a single-electron transfer (SET)/energy transfer (EnT) pathway

A new environmentally friendly plan was created to make dihydropyrano [2,3-c]pyrazole structures without using metals. This plan involves combining ethyl acetoacetate, hydrazine hydrate, aldehyde derivatives, and malononitrile in a radical tandem Knoevenagel-Michael cyclocondensation reaction. We used metal-free methylene blue (MB⁺) to create special functions that respond to light. These functions can transfer electrons and energy in water at room temperature using light as a source of energy in the air. The amount of product made is pretty consistent (between 81 and 98 %, with an average of 91.8 %), and it gets made quickly (between 3 and 7 min, with an average of 5.3 min). The important thing mentioned in the conversation is that the process can handle different types of chemicals while still being fast and giving good results. The results show that this special technique is a successful and easy way to get good results in just one step. Methylene blue is used with very little amount to make a chemical reaction happen. This leads to high amounts of product, saves energy, and is good for the environment. It helps use up all the starting materials efficiently, saves time by not needing to separate chromatography, and reduces waste. This photocatalyst is easy to use. This creates many different types of characteristics in the environment and chemicals that last a long time. The turnover number (TON) and turnover frequency (TOF) of dihydropyrano [2,3-c]pyrazole scaffolds were calculated. It is interesting that cyclization on a gram scale can be achieved, showing that this technique can be used in industries.