Rhodium‐Catalyzed Synthesis of Multiaryl‐substituted Naphthols via a Removable Directing Group

Abstract

Arene homologation employing internal alkynes as coupling partners and 2-pyridyloxyl as directing group through dual CÀH bond functionalization was accomplished using (pentamethylcyclopentadienyl)-rhodium(III) chloride dimer as a precatalyst. This protocol proved tolerant of synthetically valuable functional groups, and provided an expeditious access to highly congested naphthalene derivatives in moderate to good yields. Furthermore, the pyridyl moiety could be removed to furnish the versatile (OH)-free naphthols.

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…Unfortunately, the reaction with alkyl or heteroarylalkynes did not occur, and asymmetric alkynes resulted in very poor regioselectivity. 891 Acylation reactions were reported by Wu and Huo, using aldehydes and acyl chlorides as reactants. The first method ( Scheme 148C ) 892 uses TBHP as oxidant and follows the mechanism depicted in Scheme 118 , resulting mostly in monoacylation (difunctionalisation is substrate-dependent), giving low yields for strongly EWG-substituted phenols.…”

Substituted Naphthols: Preparations, Applications, and Reactions

“…A further example highlighting the use of the popular rhodium(III) catalyst [(Cp*RhCl 2 ) 2 ] in naphthol synthesis was shown by Cui and co‐workers. [ 51 ] Their method involves a C–H bond functionalization of 2‐pyridyloxyls 38 (pyridine nitrogen directing the C(sp 2 )‐H insertion on the phenol ring), followed by subsequent insertion of internal alkynes 39 . Two key subsequent rhodacycle formations ensue, followed by a second alkyne 39 insertion and reductive elimination to yield polyarylated naphthalenes 40 in good yields.…”

Rhodium(III)-Catalyzed Oxidative Annulation of 2,2′-Bipyridine N-Oxides with Alkynes via Dual C–H Bond Activation

“…Based on these observations and the literature precedents, − possible catalytic cycles for both transformations are given in Scheme . First, cyclometalation of 1a generates a five-membered rhodacyclic intermediate A .…”

“…Recently, Rh­(III)-catalyzed C–H bond annulation with alkynes has evolved into a powerful tool for the preparation of highly substituted polycyclic aromatic compounds. − In particular, several novel fused polycyclic (hetero)­arenes could be readily synthesized by annulation reactions of (hetero)­arenes with alkynes under Rh­(III) catalysis via double C–H activation involving chelation-assisted ortho C–H activation and subsequent rollover or nonrollover C–H activation. , Notably, the reaction pathway between rollover and nonrollover annulation can be switched by varying the reaction conditions, thereby delivering different types of products from the same substrates. For example, Miura and Satoh et al found that Rh­(III)-catalyzed rollover annulation of 1-phenyl-1 H -pyrazoles with 1 equiv of alkynes could give 4,5-disubstituted pyrazolo­[1,5- a ]­quinolones (Scheme a, right), while the nonrollover annulation of 1-phenyl-1 H -pyrazoles with 2 equiv of alkynes afforded 1-(5,6,7,8-tetrasubstituted naphthalen-1-yl)-1 H -pyrazoles as the products under slightly modified conditions (Scheme a, left) .…”