Rhodium‐Catalyzed Heterocycle Synthesis by CH Functionalization

Abstract

Rhodium complexes of +1, +2, and +3 oxidation states are adept at functionalizing CH bonds and do so via distinct mechanistic pathways. These modes of activation have been harnessed into cascade processes that lead to a wide variety of heterocycles, including isoquinolines, isoquinolones, pyridines, pyridones, indoles, lactones, and their fused polycyclic derivatives. As such, this article will focus on the chemistry that enables de novo synthesis of heterocycles rather than those that only functionalize existing heterocycles. This article is organized into three parts, starting with Part A, Rhodium(III) catalysis, which makes up the largest subfield of rhodium‐catalyzed heterocycle synthesis, and is further divided into the chemistry of alkynes, alkenes, carbenes, and nitrenes. Part B details rhodium(I) catalysis in the contexts of hydroalkenylation (e.g. alkynes), hydroarylation (e.g. alkynes), and hydroacylation (e.g. alkynes, alkenes, and ketones). The article closes with Part C, a brief discussion on the use of rhodium(II) catalysis in constructing heterocycles.

Recent advances in Rh(i)-catalyzed enantioselective C–H functionalization

“…investigated in asymmetric C-H functionalization with diverse mechanisms. [32][33][34][35][36][37][38][39][40][41][42][43][44][45] From the viewpoint of substrate activation modes, Rh-catalyzed C-H functionalization could be classified into two categories: inner-sphere mechanism and outer-sphere mechanism, which differ in the mechanism of the C-H activation step (Scheme 1). 46,47 Generally, Rh(III)-catalyzed asymmetric C-H functionalization adopts the inner-sphere mechanism by taking advantage of a chiral cyclopentadienyl (Cp) ligand, 35,38,39,[48][49][50][51] whereas Rh(II) usually coordinates with a chiral carboxylic acid to achieve the effect of asymmetric C-H functionalization via the outer-sphere mechanism, 14,[52][53][54] both of which have been well reviewed elsewhere.…”