Conjugate Addition of Indoles and Pyrroles to Dihydronitronaphthalenes in Water: Synthesis of 3,4‐Fused Tetrahydro‐β‐carbolines

Abstract

AbstractA catalyst‐free conjugate addition of indoles and pyrroles to 1,2‐dihydro‐3‐nitronaphthalenes in water has been developed. A variety of indoles containing electron‐rich and ‐deficient functional groups including aza‐indoles and pyrroles reacted smoothly with a number of dihydro‐3‐nitronaphthalenes, especially bromo derivatives. For structural elaboration, the bromo functionality (dihydronitronaphthalene unit as well as indolyl unit) of the addition products was utilized for Suzuki coupling reactions and provided moderate to good yields of the desired coupling compounds. The utility of the method was further demonstrated by the synthesis of 3,4‐fused tetrahydro‐β‐carbolines, a new class of compounds, from the addition products through reduction of the nitro group to the amine and subsequent Pictet–Spengler cyclization.