Orthogonal Syntheses of γ-Carbolinone and Spiro[pyrrolidinone-3,3']indole Derivatives in One Pot through Reaction Telescoping

Pd/NBE-Catalyzed One-Pot Modular Synthesis of Tetrahydro-γ-carbolines

Tetrahydro-γ-carbolines are especially outstanding fused heterocyclic ring systems possessing significant biological activities in the central nervous system. Here, using commercially available NBE derivatives (NBEs), we report an efficient protocol for the one-pot modular synthesis of 4-substituted tetrahydro-γ-carbolines via Catellani/aza-Michael addition cascade from easily available 3-iodo-1-tosyl-1H-indole, aziridines and olefins. This approach exhibits a wide substrate scope, good yields, scalability, and potential extension toward the synthesis of Mebhydroline analogues.

Electrochemical synthesis of γ-carbolinones via sulfonylation-triggered cyclization of indole-3-carboxamides

A novel electrochemical radical cyclization reaction of N-acryloyl-indole-3-carboxamides with sodium sulfinates as coupling partners has been developed, which delivers multi-substituted γ-carbolinones as products with up to 70% yields. This study represents the first example of the radical cyclization reaction of indole-3-carboxamides under electrochemical conditions. The reaction features a broad substrate scope of sodium sulfinates and indole-3-carboxamides, and provides a new and efficient strategy for the synthesis of γ-carbolinone derivatives.

Light-Induced Transformations of Donor-Donor Diazo Compounds Derived from N-Sulfonylhydrazones

The donor-donor carbene chemistry field is underdeveloped and often relies on harsh reaction conditions, utilizing either thermal or oxidative process with or without transition-metal catalysts. In this review, we discussed the synthesis and transformation of donor-donor diazo compounds from N-sulfonylhydrazones in the presence of light and base. The N-sulfonylhydrazones are easily accessible from the corresponding carbonyl compounds and sulfonyl hydrazides through condensation. The in situ generated N-sulfonyl anion in the presence of base would undergo the N-S bond cleavage with the aid of light to generate the donor-donor diazo compounds. The donor-donor diazo compounds showed various reactivity in the presence of light for the C-C and C-X bond formation, cyclopropanation reactions, and synthesis of nitrogen, oxygen-containing heterocyclic compounds, which all are discussed under metal-free conditions.

Visible Light Induced B-H Bond Insertion Reaction with Diazo Compounds

A protocol induced by visible light for the direct insertion of α-carbonyl carbenes into the B-H bond of amine-borane adducts has been developed under conditions that are free of metal and photocatalyst. This approach provides a straightforward route to various organoboron compounds from diazo compounds and amine-borane adducts with moderate to good yields. Mechanistic investigations reveal that this photoinduced reaction proceeds through concerted carbene insertion into the B-H bond, and the photoinduced generation of free carbene from α-diazo esters may be the rate-determining step.

Visible Light-Induced Reactions of Diazo Compounds and Their Precursors

In recent years, visible light-induced reactions of diazo compounds have attracted increasing attention in organic synthesis, leading to improvement of existing reactions, as well as to the discovery of unprecedented transformations. Thus, photochemical or photocatalytic generation of both carbenes and radicals provide milder tools toward these key intermediates for many valuable transformations. However, the vast majority of the transformations represent new reactivity modes of diazo compounds, which are achieved by the photochemical decomposition of diazo compounds and photoredox catalysis. In particular, the use of a redox-active photocatalysts opens the avenue to a plethora of radical reactions. The application of these methods to diazo compounds led to discovery of transformations inaccessible by the classical reactivity associated with carbenes and metal carbenes. In most cases, diazo compounds act as radical sources but can also serve as radical acceptors. Importantly, the described processes operate under mild, practical conditions. This Review describes this subfield of diazo compound chemistry, particularly focusing on recent advancements.

Biosynthesis of the allelopathic alkaloid gramine in barley by a cryptic oxidative rearrangement

The defensive alkaloid gramine not only protects barley and other grasses from insects but also negatively affects their palatability to ruminants. The key gene for gramine formation has remained elusive, hampering breeding initiatives. In this work, we report that a gene encoding cytochrome P450 monooxygenase CYP76M57, which we name AMI synthase (AMIS), enables the production of gramine in Nicotiana benthamiana, Arabidopsis thaliana, and Saccharomyces cerevisiae. We reconstituted gramine production in the gramine-free barley (Hordeum vulgare) variety Golden Promise and eliminated it from cultivar Tafeno by Cas-mediated gene editing. In vitro experiments unraveled that an unexpected cryptic oxidative rearrangement underlies this noncanonical conversion of an amino acid to a chain-shortened biogenic amine. The discovery of the genetic basis of gramine formation now permits tailor-made optimization of gramine-linked traits in barley by plant breeding.

Advances in heterocycle synthesis through photochemical carbene transfer reactions

Heterocyclic skeletons are commonly found in various bioactive molecules and pharmaceutical compounds, making them crucial in areas such as medicinal chemistry, materials science, and the realm of natural product synthesis. In recent years, the rapid advancements of visible light methodologies in organic synthesis have shown promising potential for the development of light-induced carbene transfer reactions. This is particularly significant as most organic molecules do not absorb visible light. Free carbene, known for its high activity, is frequently utilized for insertion reactions or cyclopropanation reactions. This review focuses on the photochemical strategy for the construction of heterocyclic skeletons, specifically highlighting the methods that employ visible light-promoted carbene transfer reactions.

Visible-light-promoted N-H functionalization of O-substituted hydroxamic acid with diazo esters

Herein we report an N-H functionalization of O-substituted hydroxamic acid with diazo esters under blue LED irradiation conditions. The present transformations could be performed efficiently under mild conditions without use of catalyst, additive and N₂ atmosphere. Interestingly, when THF and 1,4-dioxane were employed as the reaction solvents, an active oxonium ylide involved three-component reaction and an N-H insertion of carbene species into hydroxamate occurred, respectively.

Photochemical Intermolecular Cyclopropanation Reactions of Allylic Alcohols for the Synthesis of [3.1.0]-Bicyclohexanes

Cyclopropane-fused lactones are highly desirable in drug and natural products synthesis. Herein, we report on a photochemical, chemoselective reaction of aryldiazoacetates with allylic alcohols that furnishes cyclopropane-fused lactone skeletons efficiently in one step. The diastereoselectivity of the protocol was precisely controlled, and chemoselective cyclopropanation of allylic alcohols via free carbene intermediate followed by transesterification constitutes a series of bicyclic lactones in high yield without the formation of ether byproducts via typical O-H insertion reactions.

Synergistic Visible Light and Pd-Catalyzed C-H Alkylation of 1-Naphthylamines with α-Diazoesters

The combination of visible light irradiation and Pd-catalysis has been practically employed for the C-H alkylation reactions of naphthylamines and α-diazo esters, leading to the synthesis of α-naphthyl functionalized acetates via C-C bond construction under mild reaction conditions and under solvent-free conditions. The light irradiation has been proven to play a pivotal role in the reactions, probably by promoting the generation of active carbene species from α-diazo esters.

A Computational Study on the Photochemical O-H Functionalization of Alcohols with Diazoacetates

In this computational study, we provide a detailed analysis of the underlying reaction mechanism and show that a singlet carbene is initially formed. Depending on the pK_A of the alcohol, this singlet carbene can engage in direct protonation or enol formation to yield the O-H functionalization product. On the contrary, propargylic alcohols take up a dual role and form a complex with the carbene intermediate that leads to facile cyclopropenation reactions.

Unlocking novel reaction pathways of diazoalkanes with visible light

Photochemistry has recently attracted the interest of synthetic chemists to conduct photolysis reactions of diazoalkanes. In this feature article, we provide a concise overview on this field, starting with discoveries...

Salicylaldehyde-Promoted Cobalt-Catalyzed C-H/N-H Annulation of Indolyl Amides with Alkynes: Direct Synthesis of a 5-HT3 Receptor Antagonist Analogue

A cobalt-catalyzed annulation of the C(sp²)-H/N-H bond of indoloamides with alkynes assisted by 8-aminoquinoline is reported for the synthesis of six-membered indololactams. The use of salicylaldehyde as the ligand is crucial for this transformation. The protocol has a broad scope for both alkynes and indoles. Preparing an active Co complex illustrates that salicylaldehyde plays a key role in the C-H activation step. The synthetic applications are proven by the gram-scale reaction and one-step construction of the multicyclic 5-HT3 receptor antagonist.

A sustainable C-H functionalization of indoles, pyrroles and furans under a blue LED with iodonium ylides

Pyrrole and indole derivatives are functionalized via a green initiative with the dimethyl malonate derived phenyl iodonium ylide 4a in the presence of a blue LED via C-H functionalization of the respective heterocycles in methanol to generate the desired compounds 5-7 in moderate to good yields. Control experiments provide insight into the probable reaction mechanism. Finally, the strategy is successfully applied in the generation of azepino[4,5-b]indole 12a/b.