Regioselective access to substituted oxindoles via rhodium-catalyzed carbene C–H insertion

Scalable Total Syntheses of (±)-Catellatolactams A and B

The first total syntheses of (±)-catellatolactams A and B, two novel ansamacrolactams, are described in 5 and 8 steps, respectively. The strategy relies on an amidation reaction to couple the acylated Meldrum's acid and an aryl amine, a regioselective C-H insertion to construct the γ-lactam moiety, and an RCM reaction to forge the macrocycles with E-olefin. This concise and scalable synthesis provided over 200 mg of the target molecules.

Modular Synthesis of Cyclopropane-Fused N-Heterocycles Enabled by Underexplored Diazo Reagents

Cyclopropane-fused N-heterocycles are featured in various biologically active compounds and represent attractive scaffolds in medicinal chemistry. However, synthesis routes to access structurally and functionally diverse cyclopropane-fused N-heterocycles remain underexplored. Leveraging novel α-diazo acylating agents, we report a general approach for the direct and modular synthesis of cyclopropane-fused lactams from unsaturated amines. The operationally simple transformation, which proceeds through successive acylation, (3+2) cycloaddition and fragmentation, tolerates a broad range of functional groups and yields a wide spectrum of complex molecular scaffolds, including fused, bridged and spiro ring systems. We demonstrate the utility of this transformation in the concise syntheses of therapeutic agents milnaciprane and amitifadine.

Synthesis of Diaza[5]helicenes by ortho,ortho′-Fusion of ortho-Terphenyls

Double ortho-fusion in suitably substituted ortho-terphenyls was used for the synthesis of diaza[5]helicenes. Bis(carboxamido)-substituted ortho-terphenyls can be condensed to 5,9- and 6,9-diaza[5]helicenes, where substituents at the 6,10- and 5,10-positions, respectively­, are introduced with the carboxamido groups. While a twofold­ coupling sequence with intermediate protection of one amino group has to be used for 5,9-diaza[5]helicenes, a more concise sequence avoiding the protection leads to 6,9-diaza[5]helicenes. The simple heating of ortho,ortho′-diazidoterphenyls furnishes 5,8-dihydroindolo[2,3-c]carbazoles, i.e., [5]helicenes with alternating benzene and pyrrole rings.

Interrupted Intramolecular Hydroaminomethylation of N-Protected-2-vinyl Anilines: Novel Access to 3-Substitued Indoles or Indoline-2-ols

A new synthetic alternative to the synthesis of 3-methyl indoles and 3-methyl indoline-2-ols with an excellent atomic economy is presented in this study. It is demonstrated that the intramolecular interrupted hydroaminomethylation (HAM) reaction is a powerful tool for the formation of these compounds, which exhibit wide-ranging biological activity. Several N-Protected-2-vinyl anilines were synthesized and involved in the reaction producing the corresponding 3-methylindole or 3-methyl indoline-2-ol depending on the nature of the N-protecting groups.

Chiral Phosphoric Acid-Catalyzed Synthesis of Fluorinated 5,6-Dihydroindolo[1,2- c]quinazolines with Quaternary Stereocenters

A chiral phosphoric acid-catalyzed enantioselective synthesis of fluorinated 5,6-dihydroindolo[1,2- c]quinazolines has been developed by a condensation/amine addition cascade from 2-(1 H-indolyl)anilines and fluorinated ketones, giving the fluorinated aminals with quaternary stereogenic centers with excellent yields and up to 97% ee. A series of the fluorinated aromatic, aliphatic ketones, and ethyl trifluoropyruvate are suitable.

Efficient discovery of bioactive scaffolds by activity-directed synthesis

The structures and biological activities of natural products have often provided inspiration in drug discovery. The functional benefits of natural products to the host organism steers the evolution of their biosynthetic pathways. Here, we describe a discovery approach--which we term activity-directed synthesis--in which reactions with alternative outcomes are steered towards functional products. Arrays of catalysed reactions of α-diazo amides, whose outcome was critically dependent on the specific conditions used, were performed. The products were assayed at increasingly low concentration, with the results informing the design of a subsequent reaction array. Finally, promising reactions were scaled up and, after purification, submicromolar ligands based on two scaffolds with no previous annotated activity against the androgen receptor were discovered. The approach enables the discovery, in tandem, of both bioactive small molecules and associated synthetic routes, analogous to the evolution of biosynthetic pathways to yield natural products.

Intramolecular aromatic carbenoid insertion of biaryldiazoacetates for the regioselective synthesis of fluorenes

The rhodium- or copper-catalyzed intramolecular aromatic carbenoid insertion of biaryldiazoacetates offers a convenient route to fluorene carboxylates with high yields. Whereas, thermal conditions provided a mixture of two regioisomeric products when substituted biaryldiazoacetates were employed as substrates. The developed catalytic conditions displayed an excellent level of regioselectivity, presumably owing to steric effects. The insertion mechanism was assumed to be an electrophilic aromatic substitution, which was supported by preliminary mechanistic studies. A chloro-substituted fluorene derivative was efficiently synthesized and utilized as a base-sensitive protecting group of amines.

Controlling factors for C-H functionalization versus cyclopropanation of dihydronaphthalenes

Rhodium(II)-catalyzed reactions of vinyldiazoacetates with dihydronaphthalenes were systematically studied. These substrates underwent cyclopropanantion and/or the combined C-H activation/Cope rearrangement in good overall yield and with good diastereo- and enantiocontrol. The selectivity of these reactions was profoundly influenced by the nature of the chiral catalyst, the vinyldiazoacetate, and the dihydronaphthalene. The best combinations for achieving the highest selectivity in the cyclopropanation and the combined C-H activation/Cope rearrangement of 1,2-dihydronaphthalenes are methyl 2-diazopent-3-enoate (2a)/Rh(2)(S-DOSP)(4) and methyl 3-(tert-butyldimethylsilyloxy)-2-diazopent-3-enoate (2b)/Rh(2)(S-PTAD)(4). These combinations are very effective at enantiodivergent reactions of 1-methyl-1,2-dihydronaphthalenes.