Oxidative Coupling in Complexity Building Transforms

Abstract

Since many synthetic targets in organic chemistry are larger, more functionalized, and more oxidized than the starting inputs used, methods that unite fragments with an increase in oxidation state possess inherent efficiencies. Thus, the potential for complexity building transforms by union of activated or unactivated C–H, N–H, or O–H centers is considerable, and the challenge lies in how to obtain selective reactions from any two of these centers.

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…Another system consisting of a salen‐based catalyst ( 56 ) and atom‐economical oxygen as the terminal oxidant was found to be broadly effective in oxidative cross‐coupling reactions to give compounds 50 – 55 (Scheme ) . According to Kozlowski, the 2,6‐disubstituted phenol 48 should be applied as the substrate to carry out a selective cross‐coupling process and reduce the number of possible products . It was assumed that such a phenol (called Type I) should bind selectively at its para site to a less‐hindered site of a metal‐bound radical or radical cation of the second phenolic partner ( 49 ).…”

“…Recently, Egami and Katsuki developed chiral iron(salan) complexes (Scheme ), which afforded unsubstituted BINOL and 3,3′‐disubstitued derivatives with an enantiomeric excess of 64 % and up to 97 %, respectively . Progress in the asymmetric synthesis of biaryls has been briefly summarized in recent articles . The most important recent contributions are presented below.…”

“…[20] According to Kozlowski, the 2,6disubstituted phenol 48 should be applied as the substrate to carry out as elective cross-coupling process and reduce the number of possible products. [47] It was assumed that such aphenol (called Ty pe I) should bind selectively at its para site to al ess-hindered site of am etal-bound radical or radical cation of the second phenolic partner (49). Taking into account the regioselectivity of the method, substrates of type 49 were assigned as Ty pe II (2,4-, 3,4,5-, 3,5-, and 2,3,5substituted phenols) and Ty pe III (2,5-substituted phenols), as they provide para-ortho (p-o)a nd para-para (p-p)c oupled products,respectively.…”

“…[79] Hence,i ti sn ot surprising that the oxidative coupling of arenes,b eing one of the simplest ways to synthesize biaryls,w as quickly recognized as ap otential method to access optically active products. [47,76,78] Early successful reports were based on the use of copper complexes with chiral amines as catalysts for the enantioselective synthesis of BINOL derivatives under aerobic conditions (Scheme 13). [80][81][82][83] Thee nantioselectivity was significantly improved after mononuclear [84,85] and binuclear [86,87] vanadium complexes were introduced.…”

“…[89] Progress in the asymmetric synthesis of biaryls has been briefly summarized in recent articles. [47,88,90,91] Themost important recent contributions are presented below.…”