Nickel‐Catalyzed Enantioselective C?C Bond Formation through C?O Cleavage in Aryl Esters

We report the first enantioselective C C bond formation through C O bond cleavage using aryl ester counterparts. This method is characterized by its wide substrate scope and results in the formation of quaternary stereogenic centers with high yields and asymmetric induction.     

Functionalization of Organic Molecules by Transition‐Metal‐Catalyzed C(sp3)?H Activation

Transition‐metal‐catalyzed C? H activation has recently emerged as a powerful tool for the functionalization of organic molecules. While many efforts have focused on the functionalization of arenes and heteroarenes by this strategy in the past two decades, much less research has been devoted to the activation of non‐acidic C? H bonds of alkyl groups. This Minireview highlights recent work in this area, with a particular emphasis on synthetically useful methods.     

Rhodium(I)‐Catalyzed Enantioselective C?C Bond Activation

Relieving the strain : The rhodium(I)‐catalyzed activation of C C bonds in functionalized cyclobutanes opens a novel route to highly substituted carbo‐ and heterocycles. Particularly intriguing is the differentiation of enantiotopic C C bonds, which leads to the formation of highly enantiomerically enriched lactones, cyclopentanones, and cyclohexenones (see scheme).

     

Mild ArI‐Catalyzed C(sp2)?H or C(sp3)?H Functionalization/C?O Formation: An Intriguing Catalyst‐Controlled Selectivity Switch

A tandem C(sp²) H and C(sp³) H functionalization/C O bond formation catalyzed by iodine(III) reagents generated in situ has been developed. The method shows wide scope under mild conditions and exhibits an unprecedented selectivity profile that can be switched depending on the catalyst employed.     

Redox‐Neutral Rhodium‐Catalyzed C?H Functionalization of Arylamine N‐Oxides with Diazo Compounds: Primary C(sp3)?H/C(sp2)?H Activation and Oxygen‐Atom Transfer

An unprecedented rhodium(III)‐catalyzed regioselective redox‐neutral annulation reaction of 1‐naphthylamine N‐oxides with diazo compounds was developed to afford various biologically important 1H‐benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by‐products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp³) H bond and C(sp²) H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)‐catalyzed coupling of readily available tertiary aniline N‐oxides with α‐diazomalonates was also developed under external oxidant‐free conditions to access various aminomandelic acid derivatives by an O‐atom‐transfer reaction.     

Rhodium(III)‐Catalyzed C?C and C?O Coupling of Quinoline N‐Oxides with Alkynes: Combination of C?H Activation with O‐Atom Transfer

[Cp*Rh^III]‐catalyzed C H activation of arenes assisted by an oxidizing N O or N N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N O bond is well‐known to undergo O‐atom transfer (OAT) to alkynes. Despite the liability of N O bonds in both C H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox‐neutral coupling of quinoline N‐oxides with alkynes to afford α‐(8‐quinolyl)acetophenones. In this process the N O bond acts as both a directing group for C H activation and as an O‐atom donor.     

Platinum(II)‐Catalyzed Intramolecular Cyclization of o‐Substituted Aryl Alkynes through sp3 C?H Activation

Ring leader : PtCl₂ catalyzes intramolecular cyclization of o‐isopropyl or o‐benzyl aryl alkynes to give substituted indene derivatives with good yields and high selectivity. This reaction appears to proceed through an sp³ C? H activation and 1,4‐hydrogen migration pathway (see scheme).

     

Copper‐Catalyzed Intramolecular C(sp3)?H and C(sp2)?H Amidation by Oxidative Cyclization

The first copper‐catalyzed intramolecular C(sp³) H and C(sp²) H oxidative amidation has been developed. Using a Cu(OAc)₂ catalyst and an Ag₂CO₃ oxidant in dichloroethane solvent, C(sp³) H amidation proceeded at a terminal methyl group, as well as at the internal benzylic position of an alkyl chain. This reaction has a broad substrate scope, and various β‐lactams were obtained in excellent yield, even on gram scale. Use of CuCl₂ and Ag₂CO₃ under an O₂ atmosphere in dimethyl sulfoxide, however, leads to 2‐indolinone selectively by C(sp²) H amidation. Kinetic isotope effect (KIE) studies indicated that C H bond activation is the rate‐determining step. The 5‐methoxyquinolyl directing group could be removed by oxidation.