ABSTRACT
Aromatic rings are ubiquitous in organic chemistry and form the basis of many commercial products. Despite the numerous routes available for the preparation of aromatic compounds, there remain few methods that allow their conversion into synthetically useful partially saturated derivatives and even fewer that allow new C-C bonds to be formed at the same time. Here we set out to address this problem and uncover a unique catalytic partial reduction reaction that forms partially saturated azaheterocycles from aromatic precursors. In this reaction, methanol and formaldehyde are used for the reductive functionalization of pyridines and quinolines using catalytic iridium; thus, inexpensive and renewable feedstocks are utilized in the formation of complex N-heterocycles. By harnessing the formation of a nucleophilic enamine intermediate, the C-C bond-forming process reverses the normal pattern of reactivity and allows access to the C3 position of the arene. Mechanistic investigations using D-labelling experiments reveal the source of hydride added to the ring and show the reversible nature of the iridium-hydride addition.
ABSTRACT
Aromatic heterocycles are a very well represented motif in natural products and have found various applications in chemistry and material science, as well as being commonly found in pharmaceutical agents. Thus, new and efficient routes towards this class of compound are always desirable, particularly if they expand the scope of chemical methodology or facilitate more effective pathways to complex substitution patterns. This perspective covers recent developments in the de novo synthesis of aromatic heterocycles via palladium-catalysed α-arylation reactions of carbonyls, which is itself a powerful transformation that has undergone significant development in recent years.
ABSTRACT
Mechanistic studies revealed ruthenium-catalyzed direct arylations to proceed through reversible C-H bond activation and subsequent rate-limiting oxidative addition with aryl halides, which led to the development of widely applicable well-defined ruthenium(II) carboxylate catalysts.
ABSTRACT
Palladium-catalyzed intramolecular dehydrogenative direct arylations of 1,2,3-triazoles were accomplished under ambient pressure of air, which set the stage for a modular synthesis of annulated phenanthrenes through a reaction sequence comprising two distinct catalytic C-H bond functionalization reactions.
Subject(s)
Hydrogen/chemistry , Palladium/chemistry , Triazoles/chemistry , CatalysisABSTRACT
A palladium complex derived from a sterically hindered diaminochlorophosphine allowed for Suzuki-Miyaura cross-couplings of chloroarenes with ample scope and provided access to tetra-ortho-substituted bi(hetero)aryls.
ABSTRACT
Inexpensive copper catalysts enabled modular one-pot multicomponent syntheses of fully decorated triazoles through a sustainable "click" reaction/direct arylation sequence.