Continuous flow as an enabling technology: a fast and versatile entry to functionalized glyoxal derivatives.

We herein report two complementary strategies employing organolithium chemistry for the synthesis of glyoxal derivatives. Micro-mixer technology allows for the generation of unstable organometallic intermediates and their instantaneous in-line quenching with esters as electrophiles. Selective mono-addition was observed via putative stabilized tetrahedral intermediates. Advantages offered by flow chemistry technologies facilitate direct and efficient access to masked 1,2-dicarbonyl compounds while mitigating undesired by-product formation. These two approaches enable the production of advanced and valuable synthetic building blocks for heterocyclic chemistry with throughputs of grams per minute.

Continuous Flow as Enabling Technology: Synthesis of Heteroaromatic Sulfinates as Bench Stable Cross-Coupling Partners.

An enabling continuous flow setup for handling of unstable organolithium intermediates and synthesis of heteroaryl sulfinates on a multigram scale is described. The developed continuous flow process allows for the synthesis and simple isolation of heteroaryl sulfinates which are otherwise challenging to access in classical batch mode. The lithium sulfinate salts prepared by this method were shown to be efficient reaction partners in palladium catalyzed C(sp2)-C(sp2) cross-coupling to access medicinally relevant bis-heteroaryl motifs.

Dichloromethyllithium: Synthesis and Application in Continuous Flow Mode.

A simple and robust procedure for the synthesis and use of thermally unstable dichloromethyllithium in continuous flow mode is described. By utilizing residence times in the range of milliseconds for the generation and electrophilic quench of dichloromethyllithium, the straightforward synthesis of dichlorocarbinols and benzylic pinacol esters was realized at reaction temperatures of -30 °C, whereas typical temperatures in traditional batch mode are below -78 °C. The excellent purity profile obtained from the flow process allows us to directly telescope the exiting flow stream into semibatch quenches for further modifications. All transformations gave the desired products in remarkable purity and yield on gram scale with no need for chromatography.

Flow Chemistry on Multigram Scale: Continuous Synthesis of Boronic Acids within 1 s.

The benefits and limitations of a simple continuous flow setup for handling and performing of organolithium chemistry on the multigram scale is described. The developed metalation platform embodies a valuable complement to existing methodologies, as it combines the benefits of Flash Chemistry (chemical synthesis on a time scale of <1 s) with remarkable throughput (g/min) while mitigating the risk of blockages.