ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Assessment of non-standard reaction conditions for asymmetric 1,3-dipolar organocatalytic cycloaddition of nitrone with α,β-unsaturated aldehydes

Melinda Mojzesová, Mária Mečiarová, Ambroz Almássy, Roger Marti, and Radovan Šebesta

Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina CH-2, 84215 Bratislava, Slovakia

E-mail: radovan.sebesta@fns.uniba.sk

Abstract: Non-standard experimental conditions can often enhance organocatalytic reactions considerably. The current study explores the effectiveness of a range of non-standard reaction conditions for the asymmetric organocatalytic 1,3-dipolar cycloaddition of a nitrone with α,β-unsaturated aldehydes. The influence of ionic liquids, high-pressure conditions, ultrasound, microwave irradiation and ballmilling was tested as well as the flow process. Because of the low reactivity of the nitrone and unsaturated aldehydes in the 1,3-dipolar cycloaddition, cycloadducts were isolated in only moderate yields from the majority of experiments. However, high diastereo- and enantioselectivities were observed in ionic liquids under solvent-free conditions and in the flow reactor.

Keywords: dipolar cycloaddition – ball-milling – flow reactor – ionic liquids – microwave – ultrasound

Full paper is available at www.springerlink.com.

DOI: 10.1515/chempap-2015-0020

Chemical Papers 69 (5) 737–746 (2015)