Synthesis of 3-benzazepines and azepino[4,5-b]heterocyclic ring systems via intramolecular Friedel–Crafts cyclization

Route to Functionalized Tetrahydrobenzo[d]azepines via Re2O7-Mediated Intramolecular Friedel-Crafts Reaction

We describe a Re2O7-mediated intramolecular dehydrative Friedel-Crafts reaction for the efficient synthesis of various benzo-fused heterocycles such as benzazepines and benzazocines. This process is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. The potential application of this methodology was exemplified by the facile preparation of a NMDA antagonist as well as a key intermediate en route to SKF 38393.

Lewis acid-catalyzed diastereoselective carbofunctionalization of bicyclobutanes employing naphthols

Traditional radical-mediated ring-opening of bicyclo[1.1.0]butanes (BCBs) for cyclobutane synthesis suffers from poor diastereoselectivity. Although few reports on BCB ring-opening via polar mechanisms are available, the Lewis acid-catalyzed diastereoselective ring-opening of BCBs using carbon nucleophiles is still underdeveloped. Herein, we report a mild and diastereoselective Bi(OTf)₃-catalyzed ring-opening of BCBs employing 2-naphthols. The anticipated carbofunctionalized trisubstituted cyclobutanes were obtained via a bicoordinated bismuth complex and the products are formed in good to excellent yields with high regio- and diastereoselectivity. The scope of the reaction was further extended using electron-rich phenols and naphthylamine. The functionalization of the synthesized trisubstituted cyclobutanes shows the synthetic utility of the present method.

Palladium-catalyzed intramolecular carboborylation of 1,3-diene and synthesis of ABCD ring of communesins

A palladium-catalyzed intramolecular carboborylation of 1,3-diene has been developed for the synthesis of iminoindolines with a quaternary carbon centre. This method was applied to a substrate bearing several functional groups to afford a complex iminoindoline, which was subsequently converted into an ABCD ring model compound of communesins via an intramolecular Friedel-Crafts-type reaction.

Synthesis of the ABCDG ring skeleton of communesin F based on carboborylation of 1,3-diene and Bi(OTf)3-catalyzed cyclizations

Communesins, isolated from the mycelium of a strain of Penicillium sp., are cytotoxic heptacyclic indole alkaloids bearing a bis-aminal structure and two contiguous quaternary carbon centers. Toward a total synthesis of communesin F, we synthesized a pentacyclic ABCDG ring skeleton via carboborylation of 1,3-diene and a Friedel-Crafts-type cyclization, resulting in the formation of an azepine ring through a Bi(OTf)₃-catalyzed S_N2' reaction.

Synthesis of Functionalized Indolines and Dihydrobenzofurans by Iron and Copper Catalyzed Aryl C-N and C-O Bond Formation

A simple and effective one-pot, two-step intramolecular aryl C-N and C-O bond forming process for the preparation of a wide range of benzo-fused heterocyclic scaffolds using iron and copper catalysis is described. Activated aryl rings were subjected to a highly regioselective, iron(III) triflimide-catalyzed iodination, followed by a copper(I)-catalyzed intramolecular N- or O-arylation step leading to indolines, dihydrobenzofurans, and six-membered analogues. The general applicability and functional group tolerance of this method were exemplified by the total synthesis of the neolignan natural product, (+)-obtusafuran. DFT calculations using Fukui functions were also performed, providing a molecular orbital rationale for the highly regioselective arene iodination process.

Replacement of benzylic hydroxy group by vinyl or hydroxymethyl moiety at the 3-benzazepine scaffold retaining GluN2B affinity

Since overactivation of NMDA receptors is associated with neurodegenerative disorders, the design and development of subunit-selective NMDA receptor antagonists are of great interest. In order to avoid the formation of quinone-like intermediates as starting point for degradation the benzylic OH group of the lead compounds 2 was replaced by an electron rich vinyl or homologous hydroxymethyl moiety. The Bi(OTf)₃ catalyzed intramolecular Friedel-Crafts alkylation of 9a represents the key step in the synthesis of 1-vinyl substituted tetrahydro-3-benzazepine 10. Ozonolysis of 10 and subsequent reduction led to the hydroxymethyl derivative 14. The GluN2B affinities of the methyl ethers 2a, 3a and 4a and phenols 2b and 3b are very similar, respectively. It can be concluded that the ifenprodil binding site of GluN2B subunit containing NMDA receptors well tolerates a vinyl or hydroxymethyl moiety instead of the benzylic OH group. However, the selectivity has to improved, since the σ₁ affinity of the new ligands is higher than their GluN2B affinity.