1,3-Dipolar cycloadditions of 5-(4-methoxyphenyl)- and 5-(1H-indol-3-yl)-substituted (1Z,4R*,5R*)-1-(arylmethylidene)-4-benzamido-3-oxopyrazolidin-1-ium-2-ides to olefinic dipolarophiles

Abstract

1,3-Dipolar cycloadditions of (1Z,4R*,5R*)-1-(arylmethylidene)-4-benzamido-5-(4-methoxyphenyl)-3-oxopyrazolidin-1-ium-2-ides 6a–6f and their 5-(1H-indol-3-yl) analogues 6g–6j to olefinic dipolarophiles 7–9 were studied. Stereochemistry was controlled by the structure of dipoles 6 and dipolarophiles 7–9. Reactions of ortho-unsubstituted dipoles 6a–6c, 6g gave the major isomers 10 and 14 with syn-oriented protons H-3 and H-5, whilst ortho-disubstituted dipoles 6d, 6e, 6j gave cycloadducts 11 and 12 with anti-oriented protons H-3 and H-5. In comparison with their 5-phenyl-substituted analogues, dipoles 6a–6e, 6g, 6j were less reactive in cycloadditions to olefinic dipolarophiles 7–9. This was reflected in longer reaction times, lower yields, and sometimes in lower selectivity as well. The relative configurations of cycloadducts were determined by NMR.