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

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.

Green Asymmetric Organocatalysis

“…Asymmetric 1,3‐dipolar organocatalytic cycloaddition of nitrone 42 with α,β‐unsaturated aldehyde 43 proceeded under continuous‐flow conditions with high stereoselectivity. Isoxazoline 44 was obtained as only the endo diastereoisomer with 94 % ee (Scheme ) …”

Recent Advances in Mechanochemical Organic Synthesis

“…A mechanistic study of Diels-Alder reactions of selected anthracenes by Arrhenius kinetics was reported by Andersen and Mack [70]. The array of 1,3-dipolar cycloaddition reactions is recently extended with nitrones [71] and nitrile oxides [72].…”

Recent Developments on 1,3-Dipolar Cycloaddition Reactions by Catalysis in Green Solvents

“…In 2015, Šebesta and co-workers tested nine different organocatalysts and six ionic liquids ( Figure 3) in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide 66 with α,β-unsaturated aldehydes 67a-f (Scheme 12) [45].…”

“…In 2015, Šebesta and co-workers tested nine different organocatalysts and six ionic liquids ( Figure 3) in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide 66 with α,β-unsaturated aldehydes 67a-f (Scheme 12) [45]. Six ionic liquids (commercial or prepared according to the literature [45]) and two of nine organocatalysts tested in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide with α,β-unsaturated aldehydes [45]. Six ionic liquids (commercial or prepared according to the literature [45]) and two of nine organocatalysts tested in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide with α,β-unsaturated aldehydes [45].…”

“…Six ionic liquids (commercial or prepared according to the literature [45]) and two of nine organocatalysts tested in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide with α,β-unsaturated aldehydes [45]. Six ionic liquids (commercial or prepared according to the literature [45]) and two of nine organocatalysts tested in 1,3-dipolar cycloaddition of (Z)-N-benzylidene-1-phenylmethanamine oxide with α,β-unsaturated aldehydes [45].…”