Cyclobutene ring-opening of bicyclo[4.2.0]octa-1,6-dienes: access to CF3-substituted 5,6,7,8-tetrahydro-1,7-naphthyridines

Modular, automated synthesis of spirocyclic tetrahydronaphthyridines from primary alkylamines

Spirocyclic tetrahydronaphthyridines (THNs) are valuable scaffolds for drug discovery campaigns, but access to this 3D chemical space is hampered by a lack of modular and scalable synthetic methods. We hereby report an automated, continuous flow synthesis of α-alkylated and spirocyclic 1,2,3,4-tetrahydro-1,8-naphthyridines ("1,8-THNs"), in addition to their regioisomeric 1,6-THN analogues, from abundant primary amine feedstocks. An annulative disconnection approach based on photoredox-catalysed hydroaminoalkylation (HAA) of halogenated vinylpyridines is sequenced in combination with intramolecular SNAr N-arylation. To access the remaining 1,7- and 1,5-THN isomers, a photoredox-catalysed HAA step is telescoped with a palladium-catalysed C-N bond formation. Altogether, this provides a highly modular access to four isomeric THN cores from a common set of unprotected primary amine starting materials, using the same bond disconnections. The simplifying power of the methodology is illustrated by a concise synthesis of the spirocyclic THN core of Pfizer's MC4R antagonist PF-07258669.

Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes

An efficient method for the selective preparation of trifluoromethyl-substituted azepin-2-carboxylates and their phosphorous analogues has been developed via Cu(I)-catalyzed tandem amination/cyclization reaction of functionalized allenynes with primary and secondary amines.

Lossen rearrangement by Rh(III)-catalyzed C-H activation/annulation of aryl hydroxamates with alkynes: access to quinolone-containing amino acid derivatives

A convenient and robust method for the preparation of new CF₃-containing 2-quinolones has been developed via a Rh(III)-catalyzed C-H activation/Lossen rearrangement/annulation cascade of N-pivaloyloxy-arylamides with internal alkynes bearing an α-CF₃-α-amino acid moiety on the triple bond. This work expands the scope of valuable products that are available through C-H activation/annulation reactions of arylamides in organic synthesis.

Synthesis of α-CF3-substituted E-dehydroornithine derivatives via copper(i)-catalyzed hydroamination of allenes

Novel α-CF₃-substituted E-dehydroornithine derivatives have been synthesized via the Cu(i)-catalyzed hydroamination of α-CF₃-α-allenyl-α-aminocarboxylates/phosphonates with different amines.

Acyl Sonogashira Cross-Coupling: State of the Art and Application to the Synthesis of Heterocyclic Compounds

The acyl Sonogashira reaction represents an extension of Sonogashira cross-coupling to acid chlorides which replace aryl or vinyl halides, while terminal acetylenes are used as coupling partners in both reactions. The introduction of a carbonyl functional group on the alkyne backbone determines a radical change in the reactivity of the products. Indeed, α,β-alkynyl ketones can be easily converted into different heterocyclic compounds depending on the experimental conditions employed. Due to its potential, the acyl Sonogashira reaction has been deeply studied with particular attention to the nature of the catalysts and to the structures of both coupling compounds. Considering these two aspects, in this review, a detailed analysis of the literature data regarding the acyl Sonogashira reaction and its role in the synthesis of several heterocyclic derivatives is reported.

Rhodium(iii)-catalyzed CF3-carbenoid C–H functionalization of 6-arylpurines

An expedient route to access a new family of fluorine-containing purine derivatives via chelation-controlled rhodium(iii)-catalyzed carbenoid C–H functionalization has been developed.

Iodine-catalyzed synthesis of dibenzo[b,h][1,6]naphthyridine-11-carboxamides via a domino reaction involving double elimination of hydrogen bromide

An iodine-catalyzed reaction of 2-aminobenzamides and mucobromic acid was described and utilized to synthesize a variety of 6-oxo-5,6-dihydrodibenzo[b,h][1,6]naphthyridine-11-carboxamide derivatives in refluxing THF. As the two bromine atoms in mucobromic acid were found missing in the dibenzonaphthyridine products, a domino-type reaction mechanism involving a double elimination of hydrogen bromide was proposed.

Domino reaction of arylglyoxals with pyrazol-5-amines: selective access to pyrazolo-fused 1,7-naphthyridines, 1,3-diazocanes, and pyrroles

New multicomponent domino reactions of arylglyoxals with pyrazol-5-amines have been established, providing selective access to unprecedented pyrazolo-fused 1,7-naphthyridines, 1,3-diazocanes, and pyrroles (up to 52 examples). The unreported dipyrazolo-fused 1,7-naphthyridines were regioselectively synthesized through a special double [3 + 2 + 1] heteroannulation accompanied by direct C–C formation between two electrophilic sites of arylglyoxals. The unusual [3 + 3 + 1 + 1] cyclization resulted in 20 examples of novel dipyrazolo-fused 1,3-diazocanes, whereas pyrrolo[2,3-c]pyrazoles were obtained in good yields by varying arylglyoxals 1 and pyrazol-5-amines 2 in the ratio 1:2. Mechanisms of formation of these three new types of heterocycles are also proposed.

Combinatorial synthesis of fused tetracyclic heterocycles containing [1,6]naphthyridine derivatives under catalyst free conditions

A three-component reaction between an aromatic aldehyde, an amine, and tert-butyl 2,4-dioxopiperidine-1-carboxylate in EtOH at refluxing temperature gave fused tetracyclic heterocycles in high yields. The amines include 1H-indazol-5-amine, 1H-indazol-6-amine, 1H-indol-5-amine, and 1H-benzo[d]imidazol-5-amine, giving 11-aryl-3H-indazolo[5,4-b][1,6] naphthyridine, 11-aryl-1H-indazolo[6,7-b][1,6]naphthyridine, 11-aryl-3H-indolo[5,4-b][1,6]naph-thyridine, and 11-aryl-3H-imidazo[4',5':3,4]benzo[1,2-b][1,6]naphthyridine derivatives, respectively.