Diels-Alder type cycloaddition between 2-substituted indoles and ethyl α-nitrosoacrylate followed  by reduction affords 2-substituted tryptophan esters. N-Protection followed by saponification  furnishes the corresponding N           α-protected 2-substituted tryptophans suitable for peptide  synthesis. The preparation of a number of 2-substituted indoles by modified Madelung synthesis  is also described.
                                    2-取代
吲哚与乙基α-亚硝基
丙烯酸酯之间的Diels-Alder型环加成反应经过还原后,得到2-取代色
氨酸酯。随后进行N-保护和皂化,得到适用于肽合成的相应Nα-保护2-取代色
氨酸。此外,还描述了一种通过改良的Madelung合成法制备多种2-取代
吲哚的方法。