Application of Design of Experiments (DoE) Approach for the Optimization of Phase-transfer Catalyzed Biginelli Dihydropyrimidinone (DHPM) Synthesis

Abstract

The conventional Biginelli synthesis is more cumbersome and produces lower yields. Several improved methods are reported in the literature to replace the Biginelli catalyst. The design of biocompatible organic transformation is a major concern and a versatile greener procedure to construct Biginelli analogs is in great demand. Factorial design guided, energy-efficient, and versatile synthesis of 3,4-dihydropyrimidin-2-(1H)-ones (DHPM) was developed. One-factor-at-a time (OFAT) and factorial design (2<sup>3</sup>) studies were utilized for screening the independent variables. The optimum levels of potential variables (benzyl-n-triethylammonium chloride (BTEAC) and glacial acetic acid) were determined through studies. The factorial design (3<sup>2</sup>) analysis inferred the use of BTEAC (10.25 mol%) and glacial acetic acid (7.6 ml) as optimal for the 60 min condensation. Thirteen new 3,4- dihydropyrimidine-2-(1H)-one (DHPM) analogs were synthesized using optimized reaction conditions. The quaternary ammonium ion of BTEAC stabilizes the polarization of carbonyl group in aryl aldehydes and enolizable ketone (alkyl acetoacetate) to facilitate the cyclocondensation, in order to produce DHPMs through N-acyliminium ion and Michael adducts formation. The biocompatible strategy, simple product isolation (non-chromatographic method), and good to excellent yields are attractive features of this new protocol. Hence, the newly developed methodology is superior to the literature methods.