DBU‐Mediated Synthesis of Aryl Acetylenes or 1‐Bromoethynylarenes from Aldehydes

Corey-Fuchs reaction enabled synthesis of natural products: a review

Natural products can be derived from a vast array of animals, plants and microorganisms and are generally characterized by a wide spectrum of bioactive properties such as anti-viral, anti-cancer, anti-inflammatory and anti-bacterial properties. Synthesis of natural products is of paramount importance in various fields including medicine, biotechnology and agriculture. The Corey-Fuchs reaction, also known as the Ramirez Corey-Fuchs reaction, is a pivotal organic transformation and plays a significant role in the synthesis of intricate natural products and their analogues. This review article highlights the development of the Corey-Fuchs reaction in recent years towards the synthesis of complex natural products including polyketides, alkaloids, terpenoids and peptides.

Generation of Bis(pentafluorophenyl)boron Enolates from Alkynes and Their Catalyst-Free Alkyne Coupling

Carbon-carbon bond forming reactions are powerful synthetic tools for constructing organic molecular frameworks. In this study, strongly Lewis acidic bis(pentafluorophenyl)boron enolates were generated from alkynes through oxygen transfer from 2,6-dibromopyridine N-oxide using tris(pentafluorophenyl)borane [B(C6F5)3]. Boron enolates were highly reactive owing to the strong Lewis acidity of the boron centers, and thus immediately coupled with alkynes. N-Ethynylphthalimide reacted as an alkyne with 2,6-dibromopyridine N-oxide and B(C6F5)3 to form a semi-stable bis(pentafluorophenyl)boron enolate through the coordination of the carbonyl group to the boron center. This enolate underwent coupling with another alkyne.

Structural Optimization of Isoquinoline Derivatives from Lycobetaine and Their Inhibitory Activity against Neuroendocrine Prostate Cancer Cells

Neuroendocrine prostate cancer (NEPC) is a highly aggressive cancer that is resistant to hormone therapy and characterized by poor prognosis, as well as limited therapeutic options. Since the natural product lycobetaine was reported to exhibit good antitumor activities against various types of cancers, we initially simplified the scaffold of lycobetaine to obtain the active compound 1, an isoquinoline derivative with an aryl moiety substitution at the 4-position, which showed apparent antiproliferative activities against NPEC cell line LASCPC-01 in vitro. Subsequently, we carried out structural optimization and systematic structure-activity relationship (SAR) studies on compound 1, leading to the discovery of compound 46, which demonstrated potent inhibitory activities against the LASCPC-01 cell line with an IC50 value of 0.47 μM. Moreover, compound 46 displayed remarkable selectivity over prostate cancer cell line PC-3 with a selectivity index greater than 190-fold. Further cell-based mechanism studies revealed that compound 46 and lycobetaine can effectively induce G1 cell cycle arrest and apoptosis dose dependently. However, lycobetaine inhibited the expression of neuroendocrine markers, while compound 46 slightly upregulated these proteins. This suggested that compound 46 might exert its antitumor activities through a different mechanism than lycobetaine, warranting further study.

Regio- and stereocontrolled synthesis of borylated E-enynes, Z-enediynes and derivatives from alkenyl-1,2-bis-(boronates)

An efficient stereo-controlled synthesis of enyne and enediyne derivatives, via sequential Suzuki-Miyaura coupling reactions from easily prepared 1-alkene-1,2-diboronic esters and alkynyl bromides, is reported. The resulting enyne boronic esters were subjected to Borono-Mannich and Suzuki coupling reactions independently to obtain α,β-unsaturated aminoester and tri-substituted olefin derivatives, respectively. Additionally, divergent syntheses of triazole and cyclopropylboronate derivatives are also reported.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

Direct synthesis of 1,3-dithiolanes from terminal alkynes via visible light photoredox catalysis

AA visible light-mediated, metal-free, regioselective dihydrothionation of terminal aromatic as well as heteroaromatic alkynes has been achieved by using Eosin Y as a photoredox catalyst at room temperature. The protocol...

Synthesis and Photoswitching Properties of Bioinspired Dissymmetric γ-Pyrone, an Analogue of Cyclocurcumin

Cyclocurcumin (CC), a turmeric curcuminoid with potential therapeutic properties, is also a natural photoswitch that may undergo E/Z photoisomerization under UV light. To be further exploited in relevant biological applications, photoactivation under near-infrared (NIR) irradiation is required. Such requirement can be met through opportune chemical modifications, by favoring two-photon absorption (TPA) probability. Herein, a general and efficient synthesis of a biomimetic 2,6-disubstituted-γ-pyrone analogue of CC is described, motivated by the fact that molecular modeling previews an order of magnitude increase of its NIR TPA compared to CC. Three retrosynthetic pathways have been identified (i) via an aryl-oxazole intermediate or via aryl-diynone through (ii) a bottom-up or (iii) a top-down approach. While avoiding the passage through unstable synthons or low-yield intermediate reactions, only the latest approach could conveniently afford the 2,6-disubstituted-γ-pyrone analogue of CC, in ten steps and with an overall yield of 18%. The photophysical properties of our biomimetic analogue have also been characterized showing an improved photoisomerization yield over the parent natural compound. The potentially improved nonlinear optical properties, as well as enhanced stability, may be correlated to the enforcement of the planarity of the pyrone moiety leading to a quadrupolar D-π-A-π-D system.

Organocatalyzed ring-opening polymerization (ROP) of functional β-lactones: new insights into the ROP mechanism and poly(hydroxyalkanoate)s (PHAs) macromolecular structure

The organocatalyzed ROP of some 4-alkoxymethylene-β-propiolactones (BPL^ORs) towards the formation of the corresponding poly(hydroxyalkanoate)s (PHAs; PBPL^ORs) is investigated simply using basic organocatalysts of the guanidine (TBD), amidine (DBU) or phosphazene (BEMP) type.