Retrosynthesis III Et C-C bond NSOzA CO2Et OMe 18b C6Ha-p-Me Eto Imine formation CHO 21: ethyl glyoxylate 20: 2-veratry tryptamine C-C bo OMe 23: 2-veratrylindole NHNH2 OMe 24: phenylhydrazine 25: acetoveratroneRetrosynthesis III