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Scheme 30. Organocatalytic 1,3-dipolar cyclization of butyrolactone-derived cyclic imino esters 57 and alkylidene pyrazolones 60. This
figure is used with permission from Wiley-VCH Verlag [89] .
Scheme 31. Organocatalytic annulation cascade reaction of α, β-unsaturated butenolides 62 and butyrolactone-derived cyclic imino
esters 57. This figure is used with permission from the Royal Society of Chemistry [90] .
