C(sp³)—C(sp³) Bond Formation via Transition-Metal Mediated and Catalyzed Reductive Homocouplings

Abstract

C(sp 3 )-C(sp 3 ) bond coupling is of great significance in organic synthesis, among which reductive homocoupling has showed its special superiority in construction of symmetrical molecular structures. These reactions are usually operationally simple, which utilize organohalides as substrates, avoiding the handling of highly reactive organometallic reagents. The use of non-precise metals as the catalyst makes reductive homocouplings amenable for large-scale synthesis. Improved efficiency and selectivity have been observed in systems involving photoredox catalytic processes, ionic-liquids, and inorganic nanomaterials. This review aims to summarize the development of reductive couplings. In this review, various reductive homocouplings are summarized, where transition metals, such as cobalt, nickel, copper, titanium, and rhodium are involved. Photo-mediated reductive couplings are then highlighted followed by a discussion on applications of reductive couplings in natural products synthesis and polymer sciences. Keywords C(sp 3 )-C(sp 3 ) bond formation; reductive homocoupling; transition-metal catalysis; photoredox catalysis; total synthesis 形成碳碳键的偶联反应在有机合成研究中具有重 要地位. 2010 年诺贝尔化学奖被授予给理查德-赫克、 根 岸英一和铃木彰, 以表彰他们在偶联反应中的贡献. 目 前, 形成 C(sp 2 )-C(sp 2

Synthesis and Characterization of Diastereoisomeric Polyesters Derived from Bisphenols Bearing Vicinal Trifluoromethyl Groups

“…The synthetic difficulties may partially account for the lack of investigation into the impact of diastereoisomeric structures on polymer performance because sp 3 −sp 3 coupling reactions that produce vicinal stereogenic centers are rare. 33 Although the AgF-mediated homocoupling reaction could afford the CF 3 -containing monomer we designed, the use of a stoichiometric amount of AgF hampers the utilization of this approach in scalable synthesis. 34 We recently disclosed a highly efficient approach for the synthesis of poly(o-xylylene)s via reductive polymerization.…”

“…This behavior was observed in the TGA analysis of poly(para−xylylene)s (PPX), resulting in a very low char yield. 33 The UV stability of the polymer was examined by the exposure of the polymer under UV light (365 nm) for 36 h. No decomposition was observed in 1 H NMR analysis and GPC traces after the UV light exposure (Figures S3 and S4 in the SI).…”

“…Notably, part of the thermodecomposition may be due to the homolysis of the C sp 3 –C sp 3 bond between the stereogenic centers, as the formed radicals would be stabilized by the aryl group and the CF 3 substituent. This behavior was observed in the TGA analysis of poly­( para –xylylene)­s (PPX), resulting in a very low char yield . The UV stability of the polymer was examined by the exposure of the polymer under UV light (365 nm) for 36 h. No decomposition was observed in 1 H NMR analysis and GPC traces after the UV light exposure (Figures S3 and S4 in the SI).…”

Photoredox Selective Homocoupling of Propargyl Bromides

“…Visible-light-induced photoredox catalysis has emerged as a powerful synthetic tool due to its sustainability and mechanistic versatility in promoting a range of organic transformations with high levels of selectivity. , Many traditional reactions using stoichiometric redox reagents have been replaced by photoredox radical processes using sustainable photocatalysts. The Wurtz reaction of alkyl halides with sodium metal (later Ag, Li, Mg, Mn, Fe, Ni, and Zn) for homocoupled dimer synthesis could also be modified to photoredox Csp 3 –Csp 3 radical–radical homocoupling (Scheme a). Benzyl and allyl bromides have been reduced to generate benzyl and allyl radical intermediates, respectively, and their radical–radical homocoupling selectively provided the corresponding dimers. , Despite the high and similar reactivity of propargyl radicals compared to allyl and benzyl radicals, a photoredox Wurtz-type reaction of propargyl bromides has not yet been developed.…”

Homocoupling of benzyl pyridyl ethers via visible light-mediated deoxygenation

“…Bibenzyls are important motifs found in many biologically active natural products and drugs, making their efficient synthesis crucial for pharmaceutical research and development (Scheme 1). [1][2][3][4][5] Traditionally, these compounds have been synthesized via transition-metal-catalyzed C(sp 3 )-C(sp 3 ) homocoupling reactions 6 of benzyl halides, [7][8][9][10][11][12][13][14][15][16] Grignard reagents, [17][18][19] or organozinc reagents (Scheme 2a). 20 More recently, visible-light photoredox catalysis has emerged as a mild and effective alternative for bibenzyl synthesis through photoinduced reductive cleavage (Scheme 2b).…”