Reactions of Difunctional Electrophiles with Functionalized Aryllithium Compounds: Remarkable Chemoselectivity by Flash Chemistry

Continuous‐Flow Divergent Lithiation of 2,3‐Dihalopyridines: Deprotolithiation versus Halogen Dance

We describe herein the first halogen dance (HD) in continuous flow on 2-chloro-3-bromopyridine by selectively trapping a (pyridin-4-yl)lithium species that is known to undergo the halogen-dance process. In addition, this lithiated intermediate was trapped at lower temperature before the HD occurs. The HD process was extended to fluoro-iodopyridines by using various electrophiles to afford 28 examples with yields ranging from 42 to 97 % with very short residence times. Finally, scale up of the reaction was demonstrated, affording a promising space-time yield (STY) of 4.2 kg.h^-1 .L^-1 .

Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.

Regioselective Magnesiations and Zincations of Aromatics and Heterocycles Triggered by Lewis Acids

Mixed TMP‐bases (TMP=2,2,6,6‐tetramethylpiperidyl), such as TMPMgCl ⋅ LiCl, TMP₂Mg ⋅ 2LiCl, TMPZnCl ⋅ LiCl and TMP₂Zn ⋅ 2LiCl, are outstanding reagents for the metalation of functionalized aromatics and heterocycles. In the presence of Lewis acids, such as BF₃ ⋅ OEt₂ or MgCl₂, the metalation scope of such bases was dramatically increased, and regioselectivity switches were achieved in the presence or absence of these Lewis acids. Furthermore, highly reactive lithium bases, such as TMPLi or Cy₂NLi, are also compatible with various Lewis acids, such as MgCl₂ ⋅ 2LiCl, ZnCl₂ ⋅ 2LiCl or CuCN ⋅ 2LiCl. Performing such metalations in continuous flow using commercial setups permitted practical and convenient reaction conditions.

Flow Technology for the Genesis and Use of (Highly) Reactive Organometallic Reagents

In the field of organic synthesis, the advent of flow chemistry and flow microreactor technology represented a tremendous novelty in the way of thinking and performing chemical reactions, opening the doors to poorly explored or even impossible transformations using batch methods. In this Concept article, we would like to highlight the impact of flow chemistry for exploiting highly reactive organometallic reagents, and how, alongside the well-known advantages concerning safety, scalability, and productivity, flow chemistry makes possible processes that are impossible to control by using the traditional batch approach.

Generation and Reaction of Functional Alkyllithiums by Using Microreactors and Their Application to Heterotelechelic Polymer Synthesis

Flow microreactors enabled the successful generation of various functional alkyllithiums containing electrophilic functional groups, as well as the use of these alkyllithiums in subsequent reactions. The high reactivity of these series of reactions could be achieved by the extremely accurate and selective control of residence time. Moreover, integrated flow microreactor systems could be used to successfully synthesize heterotelechelic polymers with two functionalities, one at each end, via a process involving controlled anionic polymerization initiated by functional alkyllithium compounds, followed by trapping reactions with difunctional electrophiles.

Synthesis of Functionalized Ketones from Acid Chlorides and Organolithiums by Extremely Fast Micromixing

Synthesis of ketones containing various functional groups from acid chlorides bearing electrophilic functional groups and functionalized organolithiums was achieved using a flow microreactor system. Extremely fast mixing is important for high chemoselectivity.

Rapid and Mild Synthesis of Amino Acid N-Carboxy Anhydrides: Basic-to-Acidic Flash Switching in a Microflow Reactor

Polymerization of N-carboxy anhydrides (NCAs) is the primary process used to prepare polypeptides. The synthesis of various pure NCAs is key to the efficient synthesis of polypeptides. The only practical method that can be used to synthesize NCAs requires harsh acidic conditions that make acid-labile substrates unusable and results in an undesired ring opening of NCAs. Basic-to-acidic flash switching and subsequent flash dilution technology in a microflow reactor was used to demonstrate the synthesis of NCAs. It is both rapid (0.1 s) and mild (20 °C) and includes substrates containing acid-labile functional groups. The basic-to-acidic flash switching enabled both an acceleration of the desired NCA formation and avoided the undesired ring opening of NCAs. The flash dilution precluded the undesired decomposition of acid-labile functional groups. The developed process allowed the synthesis of various NCAs which cannot be readily synthesized using conventional batch methods.

Continuous-Flow Synthesis of Biaryls by Negishi Cross-Coupling of Fluoro- and Trifluoromethyl-Substituted (Hetero)arenes

A continuous-flow method for the regioselective arylation of fluoroarenes and fluoropyridines has been developed. The telescoped procedure reported here consists of a three-step metalation, zincation, and Negishi cross-coupling sequence, providing efficient access to a variety of functionalized 2-fluorobiaryl products. Precise temperature control of the metalation step, made possible by continuous-flow technology, allowed for the efficient preparation of the arylated products in high yields and short residence times. Additionally, several examples of the regioselective arylation of benzotrifluoride derivatives are also provided.