Synthesis of 7-arylethyl-5-arylpyrazolo$\left[1,5\text{-}a\right]$pyrimidines through an aza-Michael addition/nucleophilic addition/1,3-hydrogen transfer cascade

An efficient method for the synthesis of pyrazolo$\left[1,5\text{-}a\right]$pyrimidines by the tandem reactions of dienones with pyrazole-3-amine through an aza-Michael addition/nucleophilic addition/1,3-hydrogen transfer process in the presence of potassium hydroxide is described. This protocol offers access to 7-arylethyl-5-arylpyrazolo$\left[1,5\text{-}a\right]$pyrimidines in good to excellent yield. Meanwhile for 4-substituted dienones, different products, 7-arylethylene-5-arylpyrazolo$\left[1,5\text{-}a\right]$pyrimidines, are given through an aza-Michael addition/nucleophilic addition/oxidation process. A gram-scale reaction has been performed to demonstrate the potency of optimized procedure for the scale-up process.

Graphical Abstract

SYNOPSIS7-Arylethyl-5-arylpyrazolo$\left[1,5\text{-}a\right]$pyrimidines were efficiently synthesized by the reactions of 4-unsubstituted dienones with pyrazole-3-amine. In contrast, 7-arylethylene-5-arylpyrazolo$\left[1,5\text{-}a\right]$pyrimidines could be afforded by the reactions of 4-substituted dienones with pyrazole-3-amine. .