A versatile route to benzocanthinones

Deciphering complexity in Pd-catalyzed cross-couplings

Understanding complex reaction systems is critical in chemistry. While synthetic methods for selective formation of products are sought after, oftentimes it is the full reaction signature, i.e., complete profile of products/side-products, that informs mechanistic rationale and accelerates discovery chemistry. Here, we report a methodology using high-throughput experimentation and multivariate data analysis to examine the full signature of one of the most complicated chemical reactions catalyzed by palladium known in the chemical literature. A model Pd-catalyzed reaction was selected involving functionalization of 2-bromo-N-phenylbenzamide and multiple bond activation pathways. Principal component analysis, correspondence analysis and heatmaps with hierarchical clustering reveal the factors contributing to the variance in product distributions and show associations between solvents and reaction products. Using robust data from experiments performed with eight solvents, for four different reaction times at five different temperatures, we correlate side-products to a major dominant N-phenyl phenanthridinone product, and many other side products.

Visible-Light-Induced Cascade Difunctionalization of Indoles Enabled by the Synergy of Photoredox and Photoexcited Ketones: Direct Access to Alkylated Pyrrolophenanthridones

Herein, we describe a methodology to construct polycyclic pyrrolophenanthridones with an (amino)alkyl side chain that involves visible-light-induced decarboxylative radical addition for the intermolecular dearomatization of indoles and subsequent photoinduced C(sp²)-X bond activation via photoexcited ketones for an intramolecular cyclization cascade. Carboxylic acids serve both as a radical source toward indole dearomatization and as reductants to initiate an electron transfer with photoexcited N-acylindole derivatives in the reaction toward pyrrolophenantridone skeletons, which occurs under mild reaction conditions with good functional group tolerance.

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

Readily available 4-bromobenzo[c][2,7]naphthyridine undergoes regioselective direct ring metalation at C-5 with TMPMgCl∙LiCl at −40 °C. Quenching with various electrophiles gives a broad range of 5-substituted products, which are building blocks for the synthesis of heterocyclic natural products and analogues thereof. In combination with a Parham-type cyclization a novel approach to pyrido[4,3,2-mn]acridones has been worked out.

Access to 2-substituted 1-pyridin-3-yl-β-carboline derivatives by intramolecular radical cyclization-ring opening-SNAr substitution

A new method for the synthesis of 1-pyridin-3-yl-β-carboline derivatives involving an intramolecular radical reaction and S_NAr substitution, is described.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Fruitful Decades for Canthin-6-ones from 1952 to 2015: Biosynthesis, Chemistry, and Biological Activities

In this review, more than 60 natural canthin-6-one alkaloids and their structures are considered. The biosynthesis, efficient and classic synthetic approaches, and biological activities of canthin-6-one alkaloids, from 1952 to 2015, are discussed. From an analysis of their structural properties and an investigation of the literature, possible future trends for canthin-6-one alkaloids are proposed. The information reported will be helpful in future research on canthin-6-one alkaloids.

Diindolo[2,3-b:2',3'-f]pyrrolo[3,2-b]pyrroles as electron-rich, ladder-type fluorophores: synthesis and optical properties

Previously unknown ladder-type heteroacenes were synthesized in just two steps from aromatic amines, 2-nitrobenzaldehydes, and biacetyl. A recently discovered multicomponent process affording 1,4-dihydropyrrolo[3,2-b]pyrroles was followed by the Cadogan reaction, which resulted in simultaneous closure of two additional pyrrole rings. Rod-like compounds synthesized in this way were stable in the absence of light, and they were transformed into bis(tert-butoxycarbonyl) derivatives. The rigid herringbone-like structure resulted in a strong absorption in the λ=350-410 nm region and very strong violet and blue emission, which was bathochromically shifted relative to the emission of the parent 1,4-dihydropyrrolo[3,2-b]pyrroles. The optical properties of these compounds strongly suggest that the conjugation spanned the entire π system. The HOMO energy level was located at -4.6 to -5.1 eV.

Progress in the synthesis of canthine alkaloids and ring-truncated congeners

The canthines represent a fairly large subclass of β-carboline alkaloids, with the first members described 75 years ago. Over the last 60 years, many members of the parent compound, canthin-6-one (1), have been isolated from various plant sources, principally the Rutaceae and Simaroubaceae families, and recently from fungi. Structures isolated from these sources have been the subject of total synthesis, which continues to the present day. This review gives a broad overview of synthetic approaches to canthines over a 30-year period from 1982 to 2012 and summarizes recent reports on the synthesis of less well known ring-truncated congeners. These include C-ring-truncated ("ABD", 2) and A-ring-truncated ("BCD", 3) ring systems, which are providing new scaffolds for potentially useful therapeutic applications.

A novel approach to the pyridoacridine ring system: synthesis of the topoisomerase inhibitor 13-deazaascididemin

A novel approach to the pyridoacridine ring system of the ascididemin-type marine alkaloids is presented. This approach allows for the introduction of the ring A of the alkaloids by using a simple aromatic aldehyde building block. The viability of this approach is demonstrated with the synthesis of AK37, a bioactive deaza analogue of the alkaloid ascididemin. Starting from 3-cyano-4-methylquinoline, a sequence of regioselective homolytic benzoylation, annulation of a bromopyridine ring, and radical cyclization leads to the pentacyclic ring system.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review covers the literature on simple indole alkaloids and those with a nonrearranged monoterpenoid unit. Newly isolated alkaloids, structure determinations, total syntheses and biological activities are included.