Go West, Early Man: Modeling the Origin and Spread of Early Agriculture

Background: Pyrazoline derivatives have been found to possess a broad spectrum of biological activities. Among various pyrazoline derivatives, 2-pyrazolines seem to be the most frequently studied. A variety of methods have been reported for the preparation of this class of compound. However, in spite of their potential utility, some of the reported methods suffer from drawbacks such as long reaction times, cumbersome product isolation procedures and environmental concerns. Organic reactions in aqueous media have attracted increasing interest recently because of environmental issues and the understanding of biochemical processes. Ultrasound has increasingly been used in organic synthesis in the last three decades. A large number of organic reactions can be carried out in higher yields, shorter reaction time or milder conditions under ultrasound irradiation. Results: Preparation of a series of 1,3,5-triaryl-2-pyrazolines through the reaction of chalcones and phenylhydrazine hydrochloride was carried out in 83–96% yield within 1.5–2 h in sodium acetate-acetic acid aqueous solution under ultrasound irradiation. Conclusion: We have described a practical and convenient procedure for the synthesis of 1,3,5triaryl-2-pyrazolines in sodium acetate-acetic acid aqueous solution at room temperature under ultrasound irradiation. Background Pyrazoline derivatives have been found to possess a broad spectrum of biological activities such as tranquillizing, muscle relaxant, psychoanaleptic, anticonvulsant, antihypertensive, and antidepressant activities. [1-6] Among various pyrazoline derivatives, 2-pyrazolines seem to be the most frequently studied pyrazoline type compounds. A variety of methods have been reported for the preparation of this class of compounds. After the pioneering work of Fischer and Knoevenagel in the 19th century, the reaction of α,β-unsaturated aldehydes and ketones with phenylhydrazine in acetic acid by refluxing became one of the most popular methods for the preparation of 2-pyrazolines. [7] In 1998, Powers et al. [8] reported that the reaction of chalcones and phenylhydrazine hydrochloride in the presence of sodium hydroxide was carried out in the absolute ethanol at 70°C, but there is a disadvantage due to longer the reaction time (8 h). In 2005, the synthesis of 3,5-diaryl-2-pyrazolines by the reaction of chlorochalcones with phenylhydrazine in acetic acid by refluxing for 3 h was reported by Levai, [7] yet the ratio of chlorochalcones and phenylhydrazine was 1:5. These reaction condiPublished: 21 March 2007 Beilstein Journal of Organic Chemistry 2007, 3:13 doi:10.1186/1860-5397-3-13 Received: 26 January 2007 Accepted: 21 March 2007 This article is available from: http://bjoc.beilstein-journals.org/content/3/1/13 © 2007 Li et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.