Enantioselective Total Synthesis of (+)-Hinckdentine A via a Catalytic Dearomatization Approach

One-Pot Tandem Assembly of Amides, Amines, and Ketones: Synthesis of C4-Quaternary 3,4- and 1,4-Dihydroquinazolines

A multicomponent tandem assembly procedure for the synthesis of diverse C4-quaternary 3,4-dihydroquinazolines from amides, amines, and ketones has been developed. The one-pot reaction involves successive triflic anhydride mediated amide dehydration, ketimine addition, and Pictet-Spengler-like cyclization processes and affords products in up to 92% yield. Conversion of 3,4-dihydroquinazolines to the corresponding 1,4-dihydroquinazolines via a two-step N1 dealkylation and regioselective N3 functionalization protocol, including computational rationale for the observed regioselectivity, is also described.

Palladium-Catalyzed Intermolecular Heck-Type Dearomative [4 + 2] Annulation of 2H-Isoindole Derivatives with Internal Alkynes

Here, an interesting palladium-catalyzed intermolecular Heck-type dearomative [4 + 2] annulation of 2H-isoindole derivatives with internal alkynes has been developed, affording diverse polycyclic pyrrolidine scaffolds in good yield. This reaction is a useful method for the transformation of 2H-isoindole.

Palladium-Catalyzed Amination/Dearomatization Reaction of Indoles and Benzofurans

This report describes a palladium-catalyzed dearomatization and amination tandem reaction of 2,3-disubstituted indoles and benzofurans via the Catellani strategy. This reaction provides a new method for the construction of amino-substituted indoline-fused cyclic and benzofuran spiro compounds in good yields. The reaction has broad functional group compatibility and substrate scope.

Palladium-catalyzed asymmetric dearomative cyclization in natural product synthesis

Asymmetric catalysis is a rapidly growing field in modern organic chemistry and has been indispensable for the synthesis of enantioenriched materials to meet demands from the academies to pharmaceutical industries. Asymmetric dearomative cyclization catalyzed by transition metals has been a hot research area in the last decade. Fascinated by its ability to construct sterically hindered quaternary stereogenic center(s) through dearomatization and simultaneously forging new ring structure(s) through cyclization, palladium-catalyzed asymmetric dearomative cyclization has been applied to the synthesis of structurally complicated natural products and it is increasingly prevalent in the literature. In particular, the resultant product from dearomative cyclization, which usually carries one or more unsaturated C-C bond(s), allows further functional group transformations. Previously reported applications of palladium-catalyzed asymmetric dearomative cyclization in natural product synthesis are presented here and discussed in depth.

Catalytic asymmetric multiple dearomatizations of phenols enabled by a cascade 1,8-addition and Diels-Alder reaction

A direct catalytic asymmetric multiple dearomatization reaction of phenols was disclosed, which provides expedient access to a series of architecturally complex polycyclic compounds bearing four stereogenic centers in high enantiopurity. The key to achieve such a transformation is the combination of a dearomative 1,8-addition of β-naphthols to para-quinone methides generated in situ from propargylic alcohols and a subsequent intramolecular dearomative Diels–Alder reaction. Noteworthily, this protocol enrichs not only the diversity of dearomatized products but also the toolbox of dearomatization strategies.

The first chiral phosphoric acid catalyzed asymmetric multiple dearomatizations of phenols for the synthesis of bridged polycyclic compounds are reported.

Absolute Configurations of Synthetic Molecular Scaffolds from Vibrational CD Spectroscopy

Vibrational circular dichroism (VCD) spectroscopy is one of the most powerful techniques for the determination of absolute configurations (AC), as it does not require any specific UV/vis chromophores, no chemical derivatization, and no growth of suitable crystals. In the past decade, it has become increasingly recognized by chemists from various fields of synthetic chemistry such as total synthesis and drug discovery as well as from developers of asymmetric catalysts. This perspective article gives an overview about the most important experimental aspects of a VCD-based AC determination and explains the theoretical analysis. The comparison of experimental and computational spectra that leads to the final conclusion about the AC of the target molecules is described. In addition, the review summarizes unique VCD studies carried out in the period 2008-2018 that focus on the determination of unknown ACs of new compounds, which were obtained in its enantiopure form either through direct asymmetric synthesis or chiral chromatography.

Synthesis of chiral seven-membered β-substituted lactams via Rh-catalyzed asymmetric hydrogenation

Rh/bisphosphine-thiourea ligand (ZhaoPhos)-catalyzed asymmetric hydrogenation of seven-membered β-substituted α,β-unsaturated lactams was successfully developed to prepare various chiral seven-membered β-substituted lactams with good to excellent results (up to >99% conversion, 99% yield, and >99% ee).

A Pd-catalyzed domino Larock annulation/dearomative Heck reaction

A highly efficient synthesis of indolines from N-bromobenzoyl o-iodoanilines and alkynes is developed via a domino Larock annulation/dearomative Heck reaction.

Synthesis of tetracyclic indolin-3-ones through Pd-catalyzed intramolecular deacetylative dearomatization of 3-acetoxy-indoles

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles has been developed. A range of tetracyclic indolin-3-ones bearing C2-quaternary stereocenters are achieved in good yields, showing a wide substrate scope for this reaction. A preliminary enantioselective reaction is established to furnish the product in 63% ee by using (R,R,R)-phosphoramide-PE as a chiral ligand.

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles is disclosed, affording tetracyclic indolin-3-ones bearing C2-quaternary stereocenters in good yields.

Pd-catalyzed dearomative arylborylation of indoles

A palladium-catalyzed dearomative arylborylation of indoles is reported, which provides straightforward access to structurally diverse indolines bearing vicinal tetrasubstituted and borylated trisubstituted stereocenters in moderate to good yields with excellent diastereoselectivities.

Synthesis of the core structure of phalarine

Two new palladium-catalyzed reactions enabled the synthesis of the core structure of phalarine.

Palladium-catalyzed dearomative arylphosphorylation of indoles

A palladium-catalyzed dearomative arylphosphorylation reaction of indoles involving C–C/C–P bond formation is developed.

Catalytic asymmetric dearomatization (CADA) reaction-enabled total synthesis of indole-based natural products

The recent enantioselective total syntheses of natural products enabled by catalytic asymmetric dearomatization reactions of indole derivatives are presented.

Synthesis of indolo[1,2-c]quinazolines from 2-alkynylaniline derivatives through Pd-catalyzed indole formation/cyclization with N,N-dimethylformamide dimethyl acetal

An efficient strategy for the synthesis of 6-unsubstituted indolo[1,2-c]quinazolines is described. The Pd-catalyzed reaction of o-(o-aminophenylethynyl) trifluoroacetanilides with Ar-B(OH)2 afforded 2-(o-aminophenyl)-3-arylindoles, that were converted to 12-arylindolo[1,2-c]quinazolines by adding dimethylformamide dimethyl acetal (DMFDMA) to the reaction mixture after extractive work-up. This reaction outcome is different from the previously reported Pd-catalyzed sequential reaction of the same substrates with Ar-I, Ar-Br and ArN2+BF4-, that afforded 12-arylindolo[1,2-c]quinazolin-6(5H)-ones. Moreover, 12-unsubstituted indolo[1,2-c]quinazolines can be obtained both by reacting 2-(o-aminophenyl)indoles with DMFDMA or by sequential Pd-catalyzed reaction of o-(o-aminophenylethynyl)aniline with DMFDMA.

Heteroannulation of Arynes with α-Amino Imides: Synthesis of 2,2-Disubstituted Indolin-3-ones and Application to the Enantioselective Total Synthesis of (+)-Hinckdentine A

A novel heteroannulation reaction between α-amino imides and in situ generated arynes has been developed for the synthesis of 2,2-disubstituted indolin-3-ones. An enantioselective total synthesis of the marine alkaloid (+)-hinckdentine A was subsequently accomplished using this reaction as a key step. A catalytic enantioselective Michael addition of an α-aryl-α-isocyanoacetate to phenyl vinyl selenone was employed for the construction of the enantioenriched α-quaternary α-amino ester.

Non-monoterpenoid azepinoindole alkaloids

This review discusses various biological and chemical aspects of the non-monoterpenoid azepinoindole class of alkaloids, including their isolation, biosynthesis and total synthesis.

Palladium-catalyzed asymmetric dearomative alkenylation of indoles through a reductive-Heck reaction

A highly enantioselective intramolecular dearomatizing olefination of indoles has been developed through a Pd-catalyzed reductive Heck reaction.

Survey of natural products reported by Asian research groups in 2016

The new natural products reported in peer-reviewed articles in 2016 in journals with good reputations were reviewed and analyzed. The advances that Asian research groups made in the field of natural products chemistry in 2016 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on structural classification.

Total Synthesis of (+)-Gracilamine Based on an Oxidative Phenolic Coupling Reaction and Determination of Its Absolute Configuration

The enantioselective total synthesis of (+)-gracilamine (1) is described. The strategy features a diastereoselective phenolic coupling reaction followed by a regioselective intramolecular aza-Michael reaction to construct the ABCE ring system. The configuration at C3a in 1 was controlled by the stereocenter at C9a, which was selectively generated (91 % ee) by an organocatalytic enantioselective aza-Friedel-Crafts reaction developed by our research group. This synthesis revealed that the absolute configuration of (+)-gracilamine is 3aR, 4S, 5S, 6R, 7aS, 8R, 9aS.