Stereospecificity of 1,.3-dipolar cycloadditions of cyclic nitrones to (E) and (Z)-β-nitrostyrenes

Experimental and Theoretical DFT Study on Synthesis of Sterically Crowded 2,3,3,(4)5‐Tetrasubstituted‐4‐nitroisoxazolidines via 1,3‐Dipolar Cycloaddition Reactions Between Ketonitrones and Conjugated Nitroalkenes

“…Nitroalkenes 2a and 2b should be considered—due to the presence of second electron withdrawing group—to a class of highly reactive dipolarophiles. Subsequently, in contradiction to 2‐alkyl‐substituted and 2‐aryl‐substituted nitroethenes , they exist only as stable E‐isomers. Unfortunately, 2‐nitroacrylic esters do not exist as stable compounds—they are only indentified as unstable reaction intermediates .…”

Cascade oxime formation, cyclization to a nitrone, and intermolecular dipolar cycloaddition

“…The isomer 17 could arise either from the isomer 18 (for example by epimerization or via retro-Mannich reaction) or from a stepwise rather than concerted cycloaddition process. 11 From the results above, it is clear that the aldehyde 13 is amenable to the desired cascade chemistry involving oxime formation, cyclization to give a nitrone, followed by intermolecular cycloaddition. This requires an activated alkene to promote cycloaddition, otherwise (as found for compound 5) the five-membered nitrone is prone to conversion to a pyrrole ring.…”

Understanding the different reactivity of (Z)- and (E)-β-nitrostyrenes in [3+2] cycloaddition reactions. An MEDT study

“…9 Some nitroethylenes can exist as transitory unstable (Z)-isomeric form. [10][11][12][13][14][15][16] These structures have shown to have some tendency to gradually transform into the (E)-isomers.…”

“…In particular, only some minor mentions regarding the participation of (Z)-nitroethylenes in [3+2] cycloaddition (32CA) reactions can be found in the literature. 13,16 Gandol and coworkers 16 studied the course of 32CA reactions of (E)-b-nitrostyrene (E)-1 and (Z)-b-nitrostyrene (Z)-1 with 5,5-dimethylpyrroline-N-oxide 2, a ve-membered cyclic nitrone, in benzene, under kinetic control conditions (see Scheme 1). They found that the 32CA reaction involving bnitrostyrene (E)-1 gave isoxazolidine trans-3 in a 72% yield, together with isoxazolidine cis-4.…”