An Atom-Economical Approach to Conformationally Constrained Tricyclic Nitrogen Heterocycles via Sequential and Tandem Ugi/Intramolecular Diels−Alder Reaction of Pyrrole<sup>1</sup><sup>,</sup><sup>2</sup>
作者:K. Paulvannan
DOI:10.1021/jo030231z
日期:2004.2.1
and 24C) as the acid components provided trienes 22, 25b, and 25c, respectively, which upon heating at 120 °C for 12 h yielded the corresponding [4 + 2] cycloaddition products. In the case of maleic acid derivative 24a, heating the reaction mixture at 60 °C for 6 h promoted the cycloadditionreaction and provided the desired product 26a in 78% yield. In contrast, fumaric acid monoethyl ester (27a)