Continuous flow based catch and release protocol for the synthesis of alpha-ketoesters

Automated synthesis of prexasertib and derivatives enabled by continuous-flow solid-phase synthesis

Recent advances in end-to-end continuous-flow synthesis are rapidly expanding the capabilities of automated customized syntheses of small-molecule pharmacophores, resulting in considerable industrial and societal impacts; however, many hurdles persist that limit the number of sequential steps that can be achieved in such systems, including solvent and reagent incompatibility between individual steps, cumulated by-product formation, risk of clogging and mismatch of timescales between steps in a processing chain. To address these limitations, herein we report a strategy that merges solid-phase synthesis and continuous-flow operation, enabling push-button automated multistep syntheses of active pharmaceutical ingredients. We demonstrate our platform with a six-step synthesis of prexasertib in 65% isolated yield after 32 h of continuous execution. As there are no interactions between individual synthetic steps in the sequence, the established chemical recipe file was directly adopted or slightly modified for the synthesis of twenty-three prexasertib derivatives, enabling both automated early and late-stage diversification.

Immobilized Carbodiimide Assisted Flow Combinatorial Protocol to Facilitate Amide Coupling and Lactamization

Through a screen of over one hundred and 30 permutations of reaction temperatures, solvents, carbodiimide resins, and carbodiimide molar equivalences, in the presence, absence, or combination of diisopropylamine and benzotriazole additives, a convenient and first reported carbodiimide polymer-assisted flow approach to effect amide coupling and lactamization was developed. The protocol entails injecting a single solution (1:9 dimethylformamide: dichloromethane) containing a carboxylic acid and an amine or linear peptide sequence into a continuous stream of dichloromethane. The protocol remained viable in the absence of base, did not require carboxylate preactivation which, and in concert with minimal workup requirements, enabled the isolation of products in high yields. Compared to the utilization of untethered carbodiimide reagents, the flow procedure was also observed to provide a degree of racemization safety.

Batch–flow hybrid synthesis of the antipsychotic clozapine

The development of batch–flow hybrid processes is becoming an attractive prospect through which chemists can make use of the best aspects of both technologies.

A new fully heterogeneous synthesis of pyrrole-2-acetic acid derivatives

Herein, we present a new general and efficient protocol to synthesize pyrrole-2-acetic acid derivatives starting from pyrroles and β-nitroacrylates.

A Multi-Step Continuous Flow Process for the N-Demethylation of Alkaloids

Dextromethorphan was N-demethylated using the non-classical Polonovski reaction under continuous flow conditions, in two steps: initial N-oxidation with m-chloroperbenzoic acid followed by iron-catalysed N-demethylation of the resulting N-oxide.

Continuous-flow hydration-condensation reaction: Synthesis of α,β-unsaturated ketones from alkynes and aldehydes by using a heterogeneous solid acid catalyst

A simple, practical and efficient continuous-flow hydration-condensation protocol was developed for the synthesis of α,β-unsaturated ketones starting from alkynes and aldehydes by employing a heterogeneous catalyst in a flow microwave. The procedure presents a straightforward and convenient access to valuable differently substituted chalcones and can be applied on multigram scale.

Diastereoselective chain-elongation reactions using microreactors for applications in complex molecule assembly

Diastereoselective chain-elongation reactions are important transformations for the assembly of complex molecular structures, such as those present in polyketide natural products. Here we report new methods for performing crotylation reactions and homopropargylation reactions by using newly developed low-temperature flow-chemistry technology. In-line purification protocols are described, as well as the application of the crotylation protocol in an automated multi-step sequence.

A continuous flow process using a sequence of microreactors with in-line IR analysis for the preparation of N,N-diethyl-4-(3-fluorophenylpiperidin-4-ylidenemethyl)benzamide as a potent and highly selective δ-opioid receptor agonist

This article describes the design, optimisation and development of a continuous flow synthesis of N,N-diethyl-4-(3-fluorophenylpiperidin-4-ylidenemethyl)benzamide, a potent δ-opioid receptor agonist developed by AstraZeneca. The process employs a sequence of flow-based microreactors, with integrated purification employing solid-supported reagents and in-line IR analytical protocols using a newly developed ReactIR flow cell. With this monitoring device, initiation of the fourth input flow stream can be precisely controlled during the synthesis.

Nitrile Oxide 1,3-Dipolar Cycloaddition by Dehydration of Nitromethane Derivatives Under Continuous Flow Conditions

Aliphatic nitrile oxides were generated in situ, by dehydration of terminal nitro compounds, and reacted with dipolarophiles using continuous flow techniques to afford substituted isoxazolines. The yields of cycloadducts were comparable with traditional flask-based reactions but reaction times were much shorter. In-line scavenger cartridges conveniently removed by-products and unreacted reagents to give almost pure crude products. The process was demonstrated up to gram scale.

A flow-based synthesis of imatinib: the API of Gleevec

A concise, flow-based synthesis of Imatinib, a compound used for the treatment of chronic myeloid leukaemia, is described whereby all steps are conducted in tubular flow coils or cartridges packed with reagents or scavengers to effect clean product formation. An in-line solvent switching procedure was developed enabling the procedure to be performed with limited manual handling of intermediates.

Flow through reactors for organic chemistry: directly electrically heated tubular mini reactors as an enabling technology for organic synthesis

Until recently traditional heating in organic chemistry has been done with oil heating baths or using electric heat exchangers. With the advent of microwave equipment, heating by microwaves was rapidly introduced as standard method in organic chemistry laboratories, mainly because of the convenient possibility to operate at high temperature accompanied by accelerated reaction rates. In the present contribution we discuss the method of heating small, continuously operated reactors by passing electric current directly through the reactor wall as an enabling technology in organic chemistry. The benefit of this method is that the heat is generated directly inside the reactor wall. By this means high heating rates comparable to microwave ovens can be reached but at much lower cost for the equipment. A tool for the comparison of microwave heating and traditional heating is provided. As an example kinetic data for the acid catalyzed hydrolysis of methyl formate were measured using this heating concept. The reaction is not only a suitable model but also one of industrial importance since this is the main production process for formic acid.

Continuous flow enantioselective arylation of aldehydes with ArZnEt using triarylboroxins as the ultimate source of aryl groups

A continuous flow system for the synthesis of enantioenriched diarylmethanols from aldehydes is described. The system uses an amino alcohol-functionalized polystyrene resin as the catalyst, and the arylating agent is conveniently prepared by transmetallation of triarylboroxins with diethylzinc.