Eosin Y catalyzes efficiently the visible light mediated coupling of sp(3) C-H bonds adjacent to the nitrogen atom in tetrahydroisoquinoline derivatives in the absence of an external oxidant. Nitroalkanes, dialkyl malonates, malononitrile, and dialkyl phophonates were used as pronucleophiles in this metal-free, visible light oxidative coupling reaction.
Highly chemoselective, palladium(O)-catalyzed, direct cross-coupling between boronic acids and geometrically activated amides is reported. The reaction proceeds via selective activation of the N-C(O) bond, shows excellent functional group tolerance, and delivers the versatile ketone products in high yields. The observed reactivity is consistent with a decrease of nN -> pi*(c=o) conjugation resulting from destabilization of the amide ground state. Notably, the method provides direct access to acyl-metal intermediates from sterically distorted, bench-stable amide precursors under mild catalytic conditions.
A copper-catalyzed alkylarylation of alkenes with simple alkanes was achieved, which not only provided an efficient method to prepare various alkyl-substituted oxindoles, but also represented a novel strategy for selective sp(3) C-H functionalization/C-C bond formation via a free-radical cascade process. Additionally, selective activation of unactivated (sp(3))C-H and (sp(2))C-H bonds by one single step is achieved in this system, which would also provide a novel strategy for raising efficiency in C-H bond functionalization.
In this work, a 1,8-naphthalimide-derived fluorescent probe for H2S based on the thiolysis of dinitrophenyl ether is reported. This probe exhibits turn-on fluorescence detection of H2S in bovine serum and lysosome-targetable fluorescent imaging of H2S with excellent selectivity.
A C-P bond and a C-C bond are formed in the synthesis of 6-phosphorylated phenanthridines starting with readily prepared 2-isocyanobiphenyls and commercially available P-radical precursors. The radical cascade reaction comprises addition of an oxidatively generated P-centered radical to the isonitrile functionality and subsequent homolytic aromatic substitution. Various 6-phosphorylated phenanthridines are formed in moderate to excellent yield. In contrast to the currently intensively investigated direct arene phosphorylation, the arene core is constructed with concomitant phosphorylation using this approach.
The first C-H bond functionalization with amides as the coupling partners via selective activation of the amide N-C bond using rhodium(I) catalysts under highly chemoselective conditions is reported. Notably, this report constitutes the first catalytic activation of the amide N-C(O) bond by rhodium. We expect that this concept will have broad implications for using amides as coupling partners for C-H activation beyond the work described herein.
Intermolecular aminotrifluoromethylation of alkenes catalyzed by [Ru(bpy)(3)](2+) under visible light irradiation has been explored. The present photocatalytic protocol achieves highly efficient and regioselective difunctionalization of C=C bonds, leading to a variety of beta-trifluoromethylamines. The reaction is applied to "late-stage aminotrifluoromethylation" of steroid and amino acid scaffolds.
A cobalt-catalyzed C-H cyanation reaction of arenes has been developed using N-cyanosuccinimide as a new electrophilic cyanating agent. The reaction proceeds with high selectivity to afford monocyanated products with excellent functional group tolerance. Substrate scope was found to be broad enough to include a wide range of heterocycles including 6-arylpurines.
A practical and unified strategy has been described for the preparation of mono- and difluoromethylated phenanthridine derivatives using a visible-light-promoted alkylation and decarboxylation sequence from biphenyl isocyanides with ethyl bromofluoroacetate (EBFA) or ethyl bromodifluoroacetate (EBDFA). These reactions could be carried out at room temperature in good to excellent chemical yields. Both stepwise and one-pot procedures have been developed, which makes this strategy more attractive.
Dynamic covalent bonds supplied by reversible anthracene dimerization were combined with pillararene/imidazole host-guest interactions to construct double-dynamic polymers. Heating such polymers (in solution or as a gel) led to depolymerization by dissociation of either the host-guest complexes alone or the complexes and the anthracene dimers, depending on the extent of heating. The polymers reformed readily upon cooling or irradiation.
The Rh(III)-catalyzed C-8 selective direct alkylation and alkynylation of quinoline N-oxides has been developed. The reactions proceeded highly efficiently at room temperature over a broad range of substrates with excellent regioselectivity and functional group tolerance. This development demonstrates the synthetic utility of the N-oxide directing group as a stepping stone for remote C H functionalization of quinolines.
A copper-catalyzed decarboxylative trifluoromethylation of various alpha,beta-unsaturated carboxylic acids by using a stable and inexpensive solid, sodium trifluoromethanesulfinate (CF3SO2Na, Langlois reagent), was developed. In addition, an Iron-catalyzed difluoromethylation of aryl-substituted acrylic acids by using zinc difluoromethanesulfinate (DFMS, (CF2HSO2)(2)Zn, Baran reagent) via a similar radical process was also achieved.
Cationic ruthenium(II) complexes enabled oxidative C-H bond functionalizations with anilines bearing removable directing groups. The C-H/N-H bond cleavages occurred most efficiently in water as a sustainable solvent and provided general access to various bioactive indoles. Mechanistic studies provided strong support for a novel reaction manifold.
Our previous studies into visible-light-mediated aza-Henry reactions demonstrated that molecular oxygen played a vital role in catalyst turnover as well as the production of base to facilitate the nucleophilic addition of nitroalkanes. Herein, improved conditions for the generation of iminium Ions from tetrahydroisoquinolines that allow for versatile nucleophilic trapping are reported. The new conditions provide access to a diverse range of functionality under mild, anaerobic reaction conditions as well as mechanistic insights into the photoredox cycle.
A copper-catalyzed decarboxylative trifluoromethylation of various α,β-unsaturated carboxylic acids by using a stable and inexpensive solid, sodium trifluoromethanesulfinate (CF(3)SO(2)Na, Langlois reagent), was developed. In addition, an iron-catalyzed difluoromethylation of aryl-substituted acrylic acids by using zinc difluoromethanesulfinate (DFMS, (CF(2)HSO(2))(2)Zn, Baran reagent) via a similar radical process was also achieved.
A versatile aerobic catalytic system (I-2 and O-2/TBHP) for C-H functionalization is reported. This CDC (cross-dehydrogentive coupling) reaction is compatible with a large number of nucleophiles and is performed under ambient reaction conditions. The scope of the metal-free CDC is illustrated by synthesizing a variety of functionalized tetrahydroisoquinolines and N,N-dimethylaniline. The highlight of the method is a Friedel-Crafts reaction of phenols and indole with tertiary amines.
A synthetic method of isoquinolines from aryl ketone O-acyloxime derivatives and internal allkynes has been developed using [Cp*RhCl2](2) NaOAc as the potential catalyst system. The present transformation is carried out by a redox-neutral sequence of C-H vinylation via ortho-rhodation and C-N bond formation of the putative vinyl rhodium intermediate on the oxime nitrogen, where the N-O bond of oxime derivatives could work as an internal oxidant to maintain the catalytic cycle.
C-H activation of arenes has been established as an important strategy for heterocycle synthesis via annulations between arenes and unsaturated coupling partners. However, nitriles failed to act as such a coupling partner. Dioxazolones have been employed as a synthon of nitriles, and subsequent coupling with arenes such as N-sulfinylimines and benzimidates bearing a functionalizable directing group provided facile access to two classes of quinazolines under Co(III)-catalysis.
A method for cobalt-catalyzed, aminoquinoline-directed ortho-functionalization of sp(2) C-H bonds with alkenes has been developed. Reactions proceed at room temperature in trifluoroethanol solvent, use oxygen from air as an oxidant, and require Mn(OAc)(3) as a cocatalyst. Benzoic, heteroaromatic, and acrylic acid aminoquinoline amides react with ethylene as well as mono- and disubstituted alkenes affording products in good yields. Excellent functional group tolerance is observed; halogen, nitro, ether, and unprotected alcohol functionalities are compatible with the reaction conditions.
A cobalt(III)-catalyzed C-2 selective C-H alkynylation of indoles using hypervalent iodine-alkyne reagents is described. A broad range of synthetically useful functional groups (-F, -Cl, -Br, -CO2Me, -CN) were tolerated, providing an efficient and robust protocol for the synthesis of C-2 alkynylated indoles. The pyrimidyl and silyl protecting groups could be easily removed to give the corresponding 2-ethynyl-1H-indole.