Rhodium(III)-Catalyzed Oxidative Olefination of Picolinamides: Convenient Synthesis of 3-Alkenylpicolinamides

Intramolecularly O,N,O-Coordinated Tin(II) Salts: Syntheses, Structures, Cyclization, and Transition Metal Complexation

We report the syntheses of tin(II) salts of the types [L1SnX]SnX3 [L1=2,6-{(i-PrO)2(O)P}2C5H3N: 1, X=Cl; 2, X=Br], [L2SnCl]SnCl3 [L2=2-{(i-PrO)Ph(O)P}-6-{(i-PrO)2(O)P}C5H3N: 3], [L3SnX]SnX3 [L3=2,6-{MeO(O)C}2C5H3N: 4, X=Cl; 5, X=Br], [L4SnX]SnX3 [L4=2,6-{Et2N(O)C}2C5H3N: 6, X=Cl; 7, X=Br]. These compounds were obtained by addition of SnX2 to the corresponding ligand inducing autoionization of the respective tin(II) halide. The thermal stability of 1, 3, and 4 was elucidated, giving, under ester cleavage and cyclisation, the tin(II) derivatives 8-12. The reaction of [L1SnCl]SnCl3 (1) with W(CO)4(thf)2 afforded the tungsten tetracarbonyl complex [{L1SnCl}{SnCl3}W(CO)4] (13), representing the first example in which a tin(II) stannate anion and a tin(II) stannylium cation simultaneously coordinate to a transition metal centre. The compounds were characterized by single crystal X-ray diffraction analyses and in part by elemental analyses, IR and NMR spectroscopy, electrospray ionization mass spectrometry. DFT calculations accompany the experimental work.

A convenient synthesis of N-(hetero)arylamides by the oxidative coupling of methylheteroarenes with amines

An oxidative amidation of 2-methylpyridines/2-methylbenzimidazole with amines using copper acetate and elemental sulfur in DMSO to afford various N-(hetero)arylamides has been accomplished. Mechanistic studies reveal the intermediacy of N-(pyridin-2-ylmethyl)aniline and confirm the role of DMSO as the oxygen source.

A Serendipitous One-Pot Cyanation/Hydrolysis/Enamide Formation: Direct Access to 3-Methyleneisoindolin-1-ones

A direct, one-pot conversion of 2'-haloacetophenones to 3-methyleneisoindolin-1-one scaffolds using CuCN as the sole reagent without the need for moisture-free or anaerobic conditions is reported. This serendipitously discovered transformation with a broad substrate scope provides a significantly different route towards these important scaffolds. The scope of the method has also been further extended towards the synthesis of three special scaffolds, which are analogous to various bio-active drugs.

Rhodium(III)-Catalyzed Oxidative Annulation of 4-Aminoquinolines and Acrylate through Two Consecutive C(sp2)-H Activations

The C-H annulation of the five-position of quinolines and acrylates to afford heterocycles is an active field of research in organic synthesis. Herein the annulation of 4-aminoquinolines with acrylates through two consecutive C-H activations catalyzed by Rh(III) is described. The reaction proceeds with high atom efficiency under mild reaction conditions, and this protocol will provide appealing strategies for the synthesis of fused quinoline heterocycles.

Rh-Catalyzed Annulative Insertion of Terminal Olefin onto Pyridines via a C-H Activation Strategy Using Ethenesulfonyl Fluoride as Ethylene Provider

A Rh(III)-catalyzed annulative insertion of ethylene onto picolinamides was achieved, providing a portal to a class of unique pyridine-containing molecules bearing a terminal olefin moiety for diversification. Application of this method for modification of Sorafenib was also accomplished.

Rhodium-Catalyzed C(sp2 )- or C(sp3 )-H Bond Functionalization Assisted by Removable Directing Groups

In recent years, transition-metal-catalyzed C-H activation has become a key strategy in the field of organic synthesis. Rhodium complexes are widely used as catalysts in a variety of C-H functionalization reactions because of their high reactivity and selectivity. The availability of a number of rhodium complexes in various oxidation states enables diverse reaction patterns to be obtained. Regioselectivity, an important issue in C-H activation chemistry, can be accomplished by using a directing group to assist the reaction. However, to obtain the target functionalized compounds, it is also necessary to use a directing group that can be easily removed. A wide range of directed C-H functionalization reactions catalyzed by rhodium complexes have been reported to date. In this Review, we discuss Rh-catalyzed C-H functionalization reactions that are aided by the use of a removable directing group such as phenol, amine, aldehyde, ketones, ester, acid, sulfonic acid, and N-heteroaromatic derivatives.

MnCl2-Catalyzed C-H Alkylation on Azine Heterocycles

Low-valent manganese-catalyzed C-H alkylation of pyridine derivatives with both primary and challenging secondary alkyl halides was established by amide assistance. The strategy provided expedient access to alkylated pyridines with wide functional group tolerance and ample scope through weak chelation. Mechanistic studies provided strong support for a rate-determining C-H activation and a SET-type C-X scission.

Co(ii)/Cu(ii)-cocatalyzed oxidative C–H/N–H functionalization of benzamides with ketones: a facile route to isoindolin-1-ones

Co/Cu-cocatalyzed oxidative C–H/N–H annulation of amides with ketones is developed to synthesize isoindolin-1-ones.

Rhodium(iii)-catalyzed Oxidative Coupling of N-Methoxybenzamides and Ethenesulfonyl fluoride: a C–H Bond Activation Strategy for the Preparation of 2-Aryl ethenesulfonyl fluorides and Sulfonyl fluoride Substituted γ-Lactams

The synthesis of a new class of 2-aryl ethenesulfonyl fluorides was achieved via a rhodium(iii)-catalyzed sp² C–H bond activation strategy.

Total synthesis of aristolactam alkaloids via synergistic C-H bond activation and dehydro-Diels-Alder reactions

A concise total synthesis of aristolactam alkaloids by a synergistic combination of C-H bond activation and dehydro-Diels-Alder reactions is described. To achieve the synthesis two new synthetic methodologies, namely the oxidative cyclization of benzamides with vinyl sulfone leading to 3-methyleneisoindolin-1-ones via a ruthenium-catalyzed C-H bond activation, and a dehydro-Diels-Alder reaction followed by the fluoride ion mediated desulfonylation of 3-methyleneisoindolin-1-ones with benzynes, were developed. The method presented allows the opportunity for the construction of all the rings of aristolactams from easily available starting materials.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Recent advances in transition-metal catalyzed positional-selective alkenylations via twofold C–H activation directed by removable or traceless directing groups are reviewed.

Expeditious synthesis of pyrano[2,3,4-de]quinolines via Rh(iii)-catalyzed cascade C–H activation/annulation/lactonization of quinolin-4-ol with alkynes

One-step synthesis of tetracyclic pyrano[2,3,4-de]quinolones via Rh(iii)-catalyzed cascade C–H activation/annulation/lactonization is described.

Recent Advances in the C-H-Functionalization of the Distal Positions in Pyridines and Quinolines

This review summarizes recent developments in the C-H-functionalization of the distal positions of pyridines, quinolines and related azaheterocycles. While the functionalization of the C2 position has been known for a long time and is facilitated by the proximity to N1, regioselective reactions in the distal positions are more difficult to achieve and have only emerged in the last decade. Recent advances in the transition metal-catalyzed distal C-H-functionalization of these synthetically-important azaheterocycles are discussed in detail, with the focus on the scope, site-selectivity and mechanistic aspects of the reactions.

RhI/RhIII catalyst-controlled divergent aryl/heteroaryl C-H bond functionalization of picolinamides with alkynes

The ability to establish switchable site-selectivity through catalyst control in the direct functionalization of molecules that contain distinct C-H bonds remains a demanding challenge that would enable the construction of diverse scaffolds from the same starting materials. Herein we describe the realization of this goal, namely a divergent heteroaryl/aryl C-H functionalization of aromatic picolinamide derivatives, targeting two distinct C-H sites, either at the pyridine ring or at the arene unit, to afford isoquinoline or ortho-olefinated benzylamine (or phenethylamine) derivatives. This complementary reactivity has been achieved on the basis of a RhIII/RhI switch in the catalyst, resulting in different mechanistic outcomes. Notably, a series of experimental and DFT mechanistic studies revealed important insights about the mechanism of the reaction and reasons behind the divergent regiochemical outcome.

Rh(iii)-catalyzed 7-azaindole synthesis via C–H activation/annulative coupling of aminopyridines with alkynes

An efficient Rh(iii)-catalyzed 7-azaindole synthesis was developed via C–H activation/annulative coupling of aminopyridines with alkynes.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

The C-H activation/1,3-diyne strategy: highly selective direct synthesis of diverse bisheterocycles by Rh(III) catalysis

The reactivity and selectivity of 1,3-diynes in transition-metal-catalyzed CH activation is exploited to quickly assemble diverse polysubstituted bisheterocycles, which are highly important but difficult to access. By using the CH activation/1,3-diyne strategy, we overcame the challenges of selectivity (chemo-, regio-, and mono-/diannulation) and constructed seven kinds of adjacent bisheterocycles through the formation of four strategic bonds with high efficiency and high selectivity.

Synthesis of alkylidene pyrrolo[3,4-b]pyridin-7-one derivatives via RhIII-catalyzed cascade oxidative alkenylation/annulation of picolinamides

A practical Rh-catalyzed oxidative cascade ortho-olefination/annulation of picolinamides leading to pyrrolo[3,4-b]pyridines has been developed.