Development of the Vinylogous Pictet-Spengler Cyclization and Total Synthesis of (±)-Lundurine A

C-H functionalization of 2-alkyl tryptamines: direct assembly of azepino[4,5-b]indoles and total synthesis of ngouniensines

The Pictet-Spengler type condensation of tryptamine derivatives and aldehydes or ketones is a classic reaction, and has been previously applied to assemble indole-annulated 5-, 6- and 8-membered heterocyclic rings. In this work, we further expand the synthetic scope of this reaction to the 7-membered azepino[4,5-b]indole skeleton through the direct C-H functionalization of 2-alkyl tryptamines, in which the non-activated methylene group participates in a 7-membered ring formation with aldehydes. By combining this unprecedented ring-forming process with a second C-H olefination at the same carbon, the concise total synthesis of natural products ngouniensines is achieved, demonstrating the synthetic potential of the developed chemistry in simplifying retrosynthetic disconnections.

Isatogenols as Precursors for the Synthesis of Fully Substituted Indolines through Regio- and Stereoselective [3 + 2] Cycloaddition Using Various Olefins

Here, we describe a unique reactivity of isatogen derivatives bearing a hydroxy group at the C3-position (isatogenol) and their synthetic application to highly regio- and stereoselective [3 + 2] cycloaddition reactions. This method provides facile access to polyfused and highly functionalized heterocycles including consecutive stereocenters. Furthermore, DFT calculations revealed that hydrogen bonding is a key to controlling the regio- and stereoselectivity in the cycloaddition using acrylates.

Enantioselective Synthesis of Fused Butyrolactones via Organocatalytic Formal [2 + 2 + 2] Annulation of γ-Butenolides, Methylene Indolinones, and Nitroolefins

An organocatalyzed asymmetric synthesis of fused butyrolactones via formal [2 + 2 + 2] annulation between γ-butenolides, methylene indolinones, and nitroolefins in a one-pot process has been established. Products containing six contiguous stereocenters could be obtained in good yields (up to 95%) with excellent enantioselectivities (up to >99% ee) catalyzed by a l-tert-leucine-derived bifunctional thiourea catalyst.

Visible-light enabled synthesis of cyclopropane-fused indolines via dearomatization of indoles

An efficient synthesis of methylene-unsubstituted cyclopropane-fused indolines via photoredox catalyzed dearomative cyclopropanation of indole derivatives was developed. A broad range of indoles bearing a variety of functional groups were compatible...

A one-pot "back-to-front" approach for the synthesis of benzene ring substituted indoles using allylboronic acids

Synthesis of only benzene ring functionalized indoles and poly-substituted carbazoles is reported via a one-pot triple cascade benzannulation protocol. Usage of differently substituted and readily accessible allylboronic acids as a 3-carbon annulating partner enables diverse aliphatic and aromatic substitution patterns, which is still a daunting task. This scalable synthetic protocol tolerates broad scope, thus enabling further downstream modifications. As an application, carbazole based natural products glycozoline and glycozolinol were synthesized.

Lewis acid mediated cyclization: synthesis of 2 spirocyclohexylindolines

Herein, we report the synthesis of 2-spirocyclohexylindolines based on a Lewis acid mediated cyclization. This diastereoselective procedure provides the target structures in a straightforward way via dual activation.

A photochemical ring expansion of 6- to 8-membered nitrogen heterocycles by [1,3]-sigmatropic rearrangement

A new route to azocines and benzoazocines from furopyridinones is described through a photochemically induced [1,3]-sigmatropic rearrangement. The method gives access to these 8-membered nitrogen heterocycles from dimethyl squarate in four stages and with excellent atom economy by sequencing thermal and photochemical ring expansion steps under continuous flow.

Synthesis and X-ray crystallographic analysis of free base and hexafluorophosphate salts of 3,4-dihydroisoquinolines from the Bischler–Napieralski reaction

Free base and hexafluorophosphate salts of 3,4-dihydroisoquinolines from the Bischler–Napieralski reaction: potential supramolecular modulation. Centrosymmetric/enantiomorphic crystals.

Enantioselective Total Syntheses of Pentacyclic Homoproaporphine Alkaloids

Herein we report the first enantioselective total syntheses of pentacyclic homoproaporphine alkaloids by means of a route, which includes a tandem retro-oxa-Michael addition and nucleophilic substitution to generate the oxa-benzobicyclco[3.3.1]nonane core structure, a Pictet-Spengler cyclization to construct the fused B and C rings, and sequential Baeyer-Villiger oxidation and pinacol-type cyclization to install the hydroxyl-lactol moiety of D ring. With this unified route, six pentacyclic homoproaporphine alkaloids have been synthesized enantioselectively.

Harnessing a Novel Machine-Learning-Assisted Evolutionary Algorithm to Co-optimize Three Characteristics of an Electrospun Oil Sorbent

The optimization of materials is challenging as it often involves simultaneous manipulation of an assembly of condition parameters, which generates an enormous combinational space. Thus, optimization models and algorithms are widely adopted to accelerate material design and optimization. However, most optimization strategies can poorly handle multiple parameters simultaneously with limited prior knowledge. Herein, we describe a novel systematic optimization strategy, namely, machine-learning-assisted differential evolution, which combines machine learning and the evolutionary algorithm together, for zero-prior-data, rapid, and simultaneous optimization of multiple objectives. The strategy enables the evolutionary algorithm to "learn" so as to accelerate the optimization process, and also to identify quantitative interactions between the condition parameters and functional characteristics of the material. The performance of the strategy is verified by in silico simulations, as well as an application on simultaneously optimizing three characteristics, namely, water contact angle, oil absorption capacity, and mechanical strength, of an electrospun polystyrene/polyacrylonitrile (PS/PAN) material as a potential sorbent for a marine oil spill. With only 50 tests, the optimal fabrication parameters were successfully located from a combinatorial space of 50 000 possibilities. The presented platform technique offers a universal enabling technology to identify the optimal conditions rapidly from a daunting parameter space to synthesize materials with multiple desired functionalities.

Stereoselective Synthesis of Vinylcyclopropa[b]indolines via a Rh-Migration Strategy

A mild rhodium catalytic system has been developed to synthesize vinylcyclopropa[b]indolines through cyclopropanation of indoles with vinyl carbenoids generated from ring opening of cyclopropenes in situ. By employing a Rh-migration strategy, the products can be obtained with good to excellent E:Z ratios (≤99:1) and complete diastereoselectivity (≤99:1). This method is easy, has a low catalyst loading, and works for a broad range of functionalities.

Microwave-Assisted aza-Friedel-Crafts Arylation of N-Acyliminium Ions: Expedient Access to 4-Aryl 3,4-Dihydroquinazolinones

A one-pot microwave-assisted aza-Friedel-Crafts arylation of N-acyliminium ions, generated in situ from o-formyl carbamates and different amines, is reported. This metal-free protocol provides rapid access to diverse 4-aryl 3,4-dihydroquinazolinones in excellent yield without any aqueous workup. A solvent-directed process for the selective aza-Friedel-Crafts arylation of electron-rich aryl/heteroaryl/butenyl-tethered N-acyliminium ions is also described.