Rh(II) Catalyzed High Order Cycloadditions of 8-Azaheptafulvenes with N-Sulfonyl 1,2,3-Triazloes or α-Oxo Diazocompounds

Continuous Flow Synthesis of N-Sulfonyl-1,2,3-triazoles for Tandem Relay Cu/Rh Dual Catalysis

The continuous flow synthesis of N-sulfonyl-1,2,3-triazoles, which are convenient reactive azavinyl carbene precursors, for tandem relay Cu/Rh dual catalysis has been developed. Most reactions readily proceeded at 75 °C in a short residence time of 13.09 min in the presence of 2.5 mol % of CuTC. The scope of the reactions was explored by synthesizing diversely functionalized N-sulfonyl and sulfamoyl triazoles in yields ranging from 92 to 98%. To demonstrate the scalability of the process, the reaction was conducted on a 5.4 mmol scale with residence and collection times of 13.09 and 60 min, respectively. Furthermore, a series of controlled experiments were performed to investigate the compatibility of Cu and Rh in a batch or a continuous flow system. Finally, the first integrated flow system using the azavinyl carbene intermediate under the tandem relay Cu/Rh dual catalysis was developed for the synthesis of various cis-diamino enones from alkynes and sulfonyl azides.

Synthesis and Mechanistic Insights of the Formation of 3-Hydroxyquinolin-2-ones including Viridicatin from 2-Chloro-N,3-diaryloxirane-2-carboxamides under Acid-Catalyzed Rearrangements

N-Benzyl-2-chloro-N,3-diaryloxirane-2-carboxamides, easily obtained from aromatic aldehydes and anilides of dichloroacetic acid under Darzens condensation conditions, proved to be excellent starting compounds for the synthesis of 3-hydroxyindolin-2-ones, cyclohepto[b]pyrrole-2,3-diones, and 1-azaspiro[4.5]deca-3,6,9-triene-2-ones via the C(sp²)-C(sp²) bond formation in the first case and C(sp²)-C(sp³) bond formation in the second and third cases. Under optimized reaction conditions, 3-hydroxyindolin-2-ones are obtained in a one-pot process, which involves the treatment of N-benzyl-2-chloro-N,3-diaryloxirane-2-carboxamides with CF₃CO₂H or AcOH/H₂SO₄. In the case of intramolecular cyclization, the detailed reaction channels depend strongly on the substituents present in the anilide component and in the aromatic ring of the aldehyde component of N-benzyl-2-chloro-N,3-diaryloxirane-2-carboxamides, as well as the temperature and duration of the reaction. A combined experimental and DFT mechanistic study of the formation of 1-benzyl-3-hydroxy-4-arylquinolin-2(1H)-ones showed that there are three competing reaction channels: (a) ring-closure via the ipso site, (b) ring-closure via the 1,2-Cl shift, and (c) ring-closure via the ortho site. Such mechanistic insights enabled an effective one-pot gram-scale synthesis of viridicatin from benzaldehyde and 2,2-dichloro-N-(4-methoxybenzyl)-N-phenylacetamide.

Gold(I)-Catalyzed [8+2]-Cycloaddition of 8-Aryl-8-azaheptafulvenes with Allenamides and Ynamides: Regioselective Synthesis of Dihydrocycloheptapyrrole Derivatives

Gold(I)-catalyzed higher-order [8+2] cycloadditions of 8-aryl-8-azaheptafulvenes 1 with allenamides 2 and ynamides 3 were studied. 1,8-Dihydrocycloheptapyrroles 4 were achieved by a regioselective [8+2] cycloaddition of azaheptafulvenes 1 and allenamides 2 in the presence of (2,4-ditBuC₆ H₃ O)₃ PAuNTf₂ as catalyst. Besides, ynamides 3 and 8-aryl-8-azaheptafulvenes 1, undergo a regioselective [8+2] cycloaddition, to give 2-amido-1,4-dihydrocycloheptapyrroles 7 in the presence of JohnPhosAuNTf₂ as catalyst. Both reactions take place with good yields and with a variety of substituents. A plausible mechanism hypothesis suggests a nucleophilic attack of the 8-azaheptafulvene to the gold activated electron rich allene or alkyne moieties of the allenamide and ynamide, respectively.

Mechanistic insights into the Rh(i)-catalyzed transannulation of 1,2,3-thiadiazoles with alkenes, alkynes, and nitriles: Does the intermediacy of α-thiavinyl Rh-carbenoids play an important role?

Density functional theory (DFT) calculations were performed to gain an in-depth mechanistic understanding of the Rh(i)-catalyzed transannulation of 1,2,3-thiadiazoles with alkenes, alkynes, and nitriles.

Co-Catalyzed Transannulation of Pyridotriazoles with Isothiocyanates and Xanthate Esters

An efficient radical transannulation reaction of pyridotriazoles with isothiocyanates and xanthate esters was developed. This method features conversion of pyridotriazoles into two N-fused heterocyclic aromatic systems-imino-thiazolopyridines and oxo-thiazolopyridine derivatives-via one-step Co(II)-catalyzed transannulation reaction proceeding via a radical mechanism. The synthetic usefulness of the developed method was illustrated in the synthesis of amino acid derivatives and further transformations of obtained reaction products.

Light-induced metal-free transformations of unactivated pyridotriazoles

A highly efficient and practical method for incorporation of the arylmethylpyridyl moiety into diverse molecules has been developed. This method features the transition metal-free light-induced room temperature transformation of pyridotriazoles into pyridyl carbenes, which are capable of smooth arylation, X-H insertion, and cyclopropanation reactions. The synthetic usefulness of the developed method was illustrated in a facile synthesis of biologically active molecules.

Insights into the Mechanisms and Chemoselectivities of Carbamates and Amides in Reactions Involving Rh(II)-Azavinylcarbene: A Computational Study

Reactions involving Rh(II)-azavinylcarbenes (Rh(II)-AVCs) to synthesize nitrogen-containing compounds have attracted significant research interest. Despite the importance of these reactions, controlling the chemoselectivities in the reactions involving Rh(II)-AVC remains a challenge. To understand the mechanisms and factors controlling the chemoselectivities between N-H and C═O groups of carbamates and amides in reactions involving Rh(II)-AVC, computational studies were employed. The results reveal that not only the greater nucleophilicity of the N-H group than that of the carbonyl group, but also the presence of H-bonding interactions, could favor the addition of the N-H group of primary carbamates to Rh(II)-AVC. However, for secondary carbamates and amides, they could undergo either chemoselective N-H or C═O addition. Secondary carbamates with less steric hindrance, such as oxazolidinone, prefer the N-H addition mode. However, a switch in chemoselectivity (preference for the C═O addition) was revealed for the sterically hindered secondary carbamates/amides. In addition, a possible O-H addition pathway via the keto-enol tautomerization for isatin and isatoic anhydride was disregarded due to the energetically demanding barrier. Instead, a pathway involving the chemoselective C═O addition, formal [3 + 2] cycloaddition, followed by ring opening was proposed. The origins of the chemoselectivity and the factors responsible were addressed.

Diastereoselective access to 2-aminoindanonesviathe rhodium(ii)-catalyzed tandem reaction involving O–H insertion and Michael addition

A rhodium(ii)-catalyzed tandem reaction involving O–H insertion ofN-sulfonyl 1,2,3-triazoles and Michael addition has been described. A series of 2-amino-1-indanones were afforded in acceptable to good yields with high diastereoselectivities.

Rhodium(ii)-catalyzed annulation of N-sulfonyl-1,2,3-triazoles with 1,3,5-triazinanes to produce octahydro-1H-purine derivatives: a combined experimental and computational study

The Rh(ii)-catalyzed annulation of N-sulfonyl-1,2,3-triazoles with 1,3,5-triazinanes leading to the octahydro-1H-purine derivatives with moderate to good yields is described in this communication.

Rhodium(ii)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones with 1-sulfonyl-1,2,3-triazole: synthesis of cyclopropa[cd]indole and benzofuran derivatives

A novel rhodium(ii)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones and 1-sulfonyl-1,2,3-triazole is disclosed, affording cyclopropa[cd]indole and benzofuran derivatives in moderate to good yields.

Metal-free synthesis of imidazole by BF3·Et2O promoted denitrogenative transannulation of N-sulfonyl-1,2,3-triazole

The first BF₃·Et₂O promoted metal-free denitrogenative transannulation of N-sulfonyl-1,2,3-triazole was reported, leading to the synthesis of functionalized imidazoles with a broad scope.

Understanding the chemoselectivities between carbonyl and hydroxyl groups in the Rh(ii)–azavinyl carbene involved reactions

Computational studies were carried out to understand the chemoselectivities between carbonyl and hydroxyl groups in the Rh(ii)–AVC involved reactions.

Facile synthesis of pyrroloindoles via a rhodium(ii)-catalyzed annulation of 3-benzylidene-indolin-2-ones and α-imino carbenes

A novel carbenoid strategy to construct pyrrole-fused indole alkaloids.

Diversity-oriented synthesis of heterocycles and macrocycles by controlled reactions of oxetanes with α-iminocarbenes

Using N-sulfonyl triazoles as substrates, compounds as diverse as 2-imino tetrahydrofurans, 13- and 15-membered ring aza-macrocycles can be prepared selectively via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations of α-imino carbenes and oxetanes under Rh(ii)-catalysis or thermal activation. Spirocyclic N-heterocycles are also accessible by means of Buchwald-Hartwig and Pictet-Spengler cyclizations. By reaction control, substrate selection or further derivatization, a large variety of chemical structures is thus achievable. Finally, using triazoles reacting under thermal activation, interesting mechanistic insight was obtained.

Synthesis of 6-Substituted Piperidin-3-ones via Rh(II)-Catalyzed Transannulation of N-Sulfonyl-1,2,3-triazoles with Electron-Rich Aromatic Nucleophiles

A highly diastereoselective rhodium(II)-catalyzed transannulation of aldehyde-tethered N-sulfonyl triazoles with electron-rich aromatic nucleophiles is reported for the first time to afford functionalized 6-substituted piperidin-3-ones. The reaction has a broad substrate scope including both aliphatic and aromatic N-sulfonyl-1,2,3-triazoles together with various aromatic nucleophiles. The addition of a catalytic amount of Lewis acid has proven to be crucial for the yield improvement. By employing this methodology, hardly accessible piperidin-3-ones bearing quaternary carbons could be obtained.