Efficient construction of a β-naphthol library under continuous flow conditions

A β-naphthol library has been efficiently constructed utilizing a mild continuous flow procedure, relying on a tandem Friedel-Crafts reaction and starting from readily available arylacetyl chloride and alkynes. Multiple functionalized β-naphthols can be acquired within 160 s in generally high yields (up to 83%). Using an electron-rich phenylacetyl chloride derivative (4-OH- or 4-MeO-) provides spirofused triene dione as the primary product. A scale-up preparation affords a throughput of 4.70 g h-1, indicating potential large-scale application. Herein, we present a rapid, reliable, and scalable method to obtain various β-naphthols in the compound library.

Metal-Free Tunable 1,2-Difunctionalization of Terminal Alkynes: Synthesis of β-Substituted α,β-Unsaturated Ketones

A metal-free tunable 1,2-difunctionalization of the terminal alkynes showcasing a tandem installation of C-C and C-S bonds has been developed. The key enabling factor for the approach is the use of acetic acid as an acyl source to synthesize β-substituted α,β-unsaturated ketones. The reaction at room temperature leads to the regioselective acylation at the terminal carbon of alkynes, whereas at -78 °C, the acylation occurs at the more substituted carbon.

A New Pathway for the Synthesis of Ketones from Aldehydes and Sulfonylhydrazones: Is Diazo the Key Intermediate?

A new pathway via a cyclic intermediate for the synthesis of ketones from aldehydes and sulfonylhydrazone derivatives under basic conditions is proposed. Several control experiments were performed along with analysis of the mass spectra and in-situ IR spectra of the reaction mixture. Inspired by the new mechanism, an efficient and scalable method for homologation of aldehydes to ketones was developed. A wide variety of target ketones were obtained in yields of 42-95 % by simply heating the 3-(trifluoromethyl)benzene sulfonylhydrazones (3-(Tfsyl)hydrazone) for 2 h at 110 °C with aldehydes and with K2 CO3 and DMSO as base and solvent, respectively.

One-Pot Tandem Nickel-Catalyzed α-Vinyl Aldol Reaction and Cycloaddition Approach to [1,2,3]Triazolo[1,5-a]quinolines

A one-pot tandem approach to [1,2,3]triazolo[1,5-a]quinolines was developed from (E)-β-chlorovinyl ketones and 2-azidoaryl carbonyls using a sequence of α-vinyl aldol and azide-alkyne cycloaddition reactions. In particular, the intramolecular azide-alkyne cycloaddition of allenol intermediates was readily promoted by a synergistic action of NEt₃ and nickel catalysts. Given that the [1,2,3]triazolo[1,5-a]quinolines are useful synthetic precursors to α-diazoimines through ring-chain isomerization process, the subsequent denitrogenative transformations should provide ready access to valuable heterocyclic compounds.

Mechanism of Friedel-Crafts Acylation Using Metal Triflate in Deep Eutectic Solvents: An Experimental and Computational Study

In this paper, we develop a method for Friedel-Crafts acylation using metal triflate in deep eutectic solvents. Various metal triflates were tested and provided good to excellent yields of corresponding ketone products. The density functional theory calculation revealed the metal effects on the formation of active intermediate acylium triflate as well as the acidic condition. The metal triflate in the deep eutectic solvent can be recovered and reused with a little loss in the catalytic activity.

Continuous Flow Synthesis of 1,4-Benzothiazines Using Ambivalent Reactivity of (E)-β-Chlorovinyl Ketones: A Point of Reaction Control Enabled by Flow Chemistry

A continuous flow system to 1,4-benzothiazines was developed using the point of reaction control, where the ambivalent (E)-β-chlorovinyl ketones and 2,2'-dithiodianilines were confined in a diffusion controlled flow setting. The successful segregation of reactive chemical species in a flow setting allowed more defined reaction pathways that are not feasible in traditional batch reaction conditions. The point of reaction control in flow systems helps to execute the reactions often plagued with the concurrent generation of multiple chemical species.

One-Pot Synthesis of N-Hydroxypyrroles via Soft α-Vinyl Enolization of (E)-β-Chlorovinyl Ketones: A Traceless Arylsulfinate Mediator Strategy

A traceless arylsulfinate mediator strategy has been developed to switch the reaction course of β-chlorovinyl ketones with N-hydroxyamine. The soft α-vinyl enolization of (E)-β-chlorovinyl ketones was conducted in the presence of sodium arylsulfinate to give transient alkenyl sulfones that in turn reacted with NH₂OH to give novel access to N-hydroxypyrroles. The mechanistic studies revealed the initial formation of oxazine intermediates that rearranged to thermodynamically stable aromatic products, N-hydroxypyrroles, under microwave-assisted heating conditions.

Electrochemical oxidative Z-selective C(sp2)-H chlorination of acrylamides

An electrochemical method for the oxidative Z-selective C(sp²)-H chlorination of acrylamides has been developed. This catalyst and organic oxidant free method is applicable across various substituted tertiary acrylamides, and provides access to a broad range of synthetically useful Z-β-chloroacrylamides in good yields (22 examples, 73% average yield). The orthogonal derivatization of the products was demonstrated through chemoselective transformations and the electrochemical process was performed on gram scale in flow.

Chemputation and the Standardization of Chemical Informatics

The explosion in the use of machine learning for automated chemical reaction optimization is gathering pace. However, the lack of a standard architecture that connects the concept of chemical transformations universally to software and hardware provides a barrier to using the results of these optimizations and could cause the loss of relevant data and prevent reactions from being reproducible or unexpected findings verifiable or explainable. In this Perspective, we describe how the development of the field of digital chemistry or chemputation, that is the universal code-enabled control of chemical reactions using a standard language and ontology, will remove these barriers allowing users to focus on the chemistry and plug in algorithms according to the problem space to be explored or unit function to be optimized. We describe a standard hardware (the chemical processing programming architecture-the ChemPU) to encompass all chemical synthesis, an approach which unifies all chemistry automation strategies, from solid-phase peptide synthesis, to HTE flow chemistry platforms, while at the same time establishing a publication standard so that researchers can exchange chemical code (χDL) to ensure reproducibility and interoperability. Not only can a vast range of different chemistries be plugged into the hardware, but the ever-expanding developments in software and algorithms can also be accommodated. These technologies, when combined will allow chemistry, or chemputation, to follow computation-that is the running of code across many different types of capable hardware to get the same result every time with a low error rate.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

Due to their intrinsic physical properties, which includes being able to perform as volatile liquids at room and biological temperatures, fragrance ingredients/intermediates make ideal candidates for continuous-flow manufacturing. This review highlights the potential crossover between a multibillion dollar industry and the flourishing sub-field of flow chemistry evolving within the discipline of organic synthesis. This is illustrated through selected examples of industrially important transformations specific to the fragrances and flavours industry and by highlighting the advantages of conducting these transformations by using a flow approach. This review is designed to be a compendium of techniques and apparatus already published in the chemical and engineering literature which would constitute a known solution or inspiration for commonly encountered procedures in the manufacture of fragrance and flavour chemicals.

One-Pot Synthesis of (Z)-β-Halovinyl Ketones via the Cascade of Sonogashira Coupling and Hydrohalogenation

Herein, we report an efficient method for the synthesis of (Z)-β-halovinyl ketones through a one-pot Sonogashira coupling and hydrohalogenation reaction promoted by palladium-copper catalyst and Brønsted acid. The ynone intermediates are generated in situ from readily available acid chlorides and terminal alkynes at room temperature, which are directly converted to (Z)-β-halovinyl ketones by treating with triflic acid. This method avoids the use of an external halogen source and features broad substrate scope, high yield, and good to excellent stereoselectivity.

Palladium-catalyzed sequential acylation/annulation of indoles with acyl chlorides using primary amine as the directing group

An efficient, palladium(ii)-catalyzed, C(sp²)–H acylation/annulation of indoles with acyl chlorides for the synthesis of substituted indolo[1,2-a]quinazolines is reported.

Pd-Catalyzed Selective Chlorination of Acrylamides at Room Temperature

In this Letter, the transition-metal-catalyzed chlorination of alkenes is reported. In the presence of the commercially available and inexpensive N-chlorosuccinimide and without additive, the Pd-catalyzed chlorination of acrylamides by C-H bond activation was developed at room temperature under air. Under these mild reaction conditions, the versatility of the methodology was demonstrated as an array of acrylamides was functionalized to selectively provide the corresponding difficult-to-synthesize chlorinated olefins as a single Z stereoisomer. Mechanistic studies were conducted to get insights into the reaction mechanism, and post-functionalization reactions further demonstrated the synthetic utility of the approach toward the access to high value-added chlorinated compounds.

Direct amide formation in a continuous-flow system mediated by carbon disulfide

We report a direct flow-based synthesis of amides. The developed approach is prominently simple and various aliphatic and aromatic amides were synthetized with excellent yields. The technology is considerably robust and easy scale-up was carried out.