Abstract

A catalyst-free, site-selective diverse functionalization of latent C-H bonds in 1-aryl-beta-carbolines and natural norharmane and harmine has been accomplished. This method enables the functionalization of 1-aryl-beta-carbolines as C6-chlorination, C6-bromination, and C4-nitration employing cost-effective, eco-friendly reagents such as trichloroisocyanuric acid (TCCA), N-bromosuccinimide (NBS) and tert-butyl nitrite (TBN), respectively. Pleasingly, these catalyst-/additive-free strategies were suitable with a broad range of substrate functionalities of different electronic nature, providing moderate to good yields of functionalized 1-aryl-beta-carbolines. The critical/sensitive functionalities such as -CF3, -NO2, -CN, and 1-(thiophen-2-yl)-beta-carboline were successfully employed, offering corresponding C6-halogenated or C4-nitrated products without strain. Furthermore, site-selective chlorination and bromination of two natural alkaloids such as harmine, norharmane were realized, resulting in corresponding halogenated products, including natural product eudistomin-N. In addition, we also employed these products in further diversification through -NO2 reduction and Suzuki (C-C) coupling of brominated compounds to deliver a C6-arylated product.