An Epoxide-Mediated Deprotection Method for Acidic Amide Auxiliary

A Mechanism Study for Self-Cleaving Chlorotetrafluoroethylsulfinyl (-SOCF2CF2Cl)-Directed Pd(II)-Catalyzed C-H Activation

A mechanism study for Pd(II)-catalyzed C(sp³)-H activation using a self-cleaving chlorotetrafluoroethylsulfinyl (-SOCF₂CF₂Cl) auxiliary as a directing group is reported. Mechanistic studies reveal that (1) the auxiliary group is crucial for C(sp³)-H activation, (2) the reaction undergoes a C(sp³)-H olefination-Michael addition-removal of the auxiliary sequence, (3) the removal of the auxiliary (SOR_f) is most likely the alcoholic solvolysis of the -SOCF₂CF₂Cl group on the N-tri-substituted sulfonamides, and (4) the C(sp³)-H cleavage is involved in the rate-determining step.

Synthesis of γ-Lactams via Pd(II)-Catalyzed C(sp3)-H Olefination Using a Self-Cleaving Polyfluoroethylsulfinyl Directing Group

A monodentate directing group, 2-chlorotetrafluoroethylsulfinylmide (-NHSOCF₂CF₂Cl), for inert C(sp³)-H bond activation is reported. This directing group shows efficient ability in Pd(II)-catalyzed C(sp³)-H olefination. The desired olefination products undergo subsequent Michael addition and in situ expulsion of the auxiliary to provide the free NH γ-lactam products. Preliminary mechanistic studies reveal that the auxiliary group is crucial for C(sp³)-H activation.

Systematic Investigation of the Scope of Transannular C-H Heteroarylation of Cyclic Secondary Amines for Synthetic Application in Medicinal Chemistry

Transannular C-H heteroarylation of amines provides rapid access to complex scaffolds that are otherwise difficult to synthesize. Wide adaptation of this emerging reaction for medicinal chemistry requires a broad understanding of substrate scope and more robust experimental conditions. In this article, we report a new ligand to promote the transannular reaction of a range of fused- and bridged-bicyclic secondary amines with a broad set of heteroarenes. The method was also successfully applied to the arylation of one spiro-bicyclic amine, a class of substrates that has not been studied in the context of transannular C-H activation reactions. The broad application of this transannular C-H heteroarylation methodology is currently hampered by the difficulty of removing the directing group. The development of a new directing group that is easier to remove will expand the utility of this reaction.

Carbon-Carbon Bond Formation of Trifluoroacetyl Amides with Grignard Reagents via C(O)-CF3 Bond Cleavage

The reaction of trifluoroacetyl amides with Grignard reagent for the substitution of CF₃ group with various alkyl or aryl groups is described. A variety of aryl, quinolin-8-yl, and (hetero)alkyl functional groups as well as F, Cl, and Br atoms are well tolerated. These moisture-stable and easily available trifluoroacetyl amides can be conveniently obtained and used as new versatile precursors for isocyanates. The control experiments show that the reaction proceeds via an isocyanate intermediate and/or alkoxide/amide dual anionic intermediate.

Iridium-Catalyzed Benzylamine C-H Alkenylation Enabled by Pentafluorobenzoyl as the Directing Group

The first iridium-catalyzed oxidative alkeynylation of benzylamines with acrylates enabled by a new directing group pentafluorobenzoyl has been developed. The reaction proceeded efficiently in the presence of silver acetate as oxidant and chlorobenzene as solvent. A good range of benzylamines could be selectively monoalkenylated without interfering with further aza-Michael addition. The kinetic isotope effect experiments showed that C-H activation is not the rate-limiting step. In addition, a five-membered iridacycle species was isolated and established as the possible key intermediate.

Enantioselective C-H Arylation and Vinylation of Cyclobutyl Carboxylic Amides

Chiral mono-N-protected aminomethyl oxazoline (MPAO) ligands are found to promote enantioselective C-H arylation and vinylation of the cyclobutyl carboxylic acid derivatives via Pd(II)/Pd(IV) redox catalysis. This ligand scaffold overcame two important limitations of the previous MPAHA (mono-N-protected α-amino-O-methylhydroxamic acid) ligands-enabled asymmetric C-H activation/C-C coupling reactions of cyclic carboxylic amides through Pd(II)/Pd(0) catalysis: substrates containing α-hydrogen atoms are not compatible; vinylation has not been developed. Sequential C-H arylation and vinylation of cyclobutanes are also accomplished to construct three consecutive chiral centers on the crowded cyclobutane rings, rendering this reaction highly versatile for the preparation of chiral cyclobutanes.