Synthesis of Pyrazoles Based on Functionalized Allenoates

Abstract

Regiospecific synthesis of pyrazole-3-carboxylate derivatives by 1,3-dipolar cycloaddition of diazomethane with allenoates in presence of triethylamine is demonstrated. Reaction of allenoates with stearic acid moiety containing diazoketone is explored under ultrasonic conditions. Novel derivatives of pyrazole were achieved in excellent yields. INTRODUCTION Among compounds containing nitrogen heterocyclic frameworks, pyrazole is one of most useful building blocks for various biologically active molecules. The biological activities of these compounds have been widely used as antidiabetic, antiviral, antimicrobial, antibacterial, anticancer agents. In addition to their biological importance, pyrazoles play important role as catalysts, molecular magnetic devices and sensors. 1,3-Dipolar cycloaddition reactions of diazo compounds to double and triple bonds are well known and documented. In contrast, studies including this methodology with regard to allenes have received much less attention. In consideration of biological activity of compounds bearing the pyrazole moiety we planned the synthesis of series of pyrazole derivatives from functionalized allenoates. RESULTS AND DISCUSSION Allenoates 2a-f were obtained from N-phthalyl amino acids 1a-c and fatty acids 1d-f. Thionyl chloride was used to convert acids 1a-f to their corresponding acid chlorides. The reaction of acid chlorides with HETEROCYCLES, Vol. 89, No. 3, 2014 641