Oxiranyl Anion Methodology Using Microflow Systems

Practical synthesis of photochromic diarylethenes in integrated flow microreactor systems

An effective method for the synthesis of photochromic diarylethenes through the generation of heteroaryllithiums and subsequent reaction with octafluorocyclopentene has been developed by using integrated flow microreactor systems. Reactions can be conducted without using cryogenic conditions by virtue of effective temperature and residence time control, although much lower temperatures (<-78 °C) are needed for batch macroreactions. Moreover, the synthesis of unsymmetrical diarylethenes, which is difficult to achieve when using conventional batch macrosystems, has been accomplished based on the selective introduction of one aryl group to give arylheptafluorocyclopentene followed by the introduction of another aryl group. The productivity of the laboratory-scale system is approximately 0.5 mmol min(-1). Therefore, the present integrated flow microreactor method serves as a practical way of synthesizing various photochromic diarylethene derivatives.

Homocoupling of aryl halides in flow: Space integration of lithiation and FeCl(3) promoted homocoupling

The use of FeCl₃ resulted in a fast homocoupling of aryllithiums, and this enabled its integration with the halogen–lithium exchange reaction of aryl halides in a flow microreactor. This system allows the homocoupling of two aryl halides bearing electrophilic functional groups, such as CN and NO₂, in under a minute.

Green and sustainable chemical synthesis using flow microreactors

Several features that allow flow microreactors contribute to green and sustainable chemical synthesis are presented: (1) For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in batch macroreactors. Better controllability, by virtue of fast mixing based on short diffusion paths in microreactors, however, leads to a higher selectivity of the products, based on kinetics considerations. Therefore, less waste is produced. (2) Reactions involving highly unstable intermediates usually require very low temperatures when they are conducted in macrobatch reactors. By virtue of short residence times, flow microreactors enable performing such reactions at ambient temperatures, avoiding cryogenic conditions and minimizing the energy required for cooling. (3) By virtue of the precise residence time control, flow microreactors allow to avoid the use of auxiliary substances such as protecting groups, enabling highly atom- and step-economical straightforward syntheses. The development of several test plants based on microreaction technology has proved that flow microreactor synthesis can be applied to the green and sustainable production of chemical substances on industrial scales. (4) Microreactor technology enables on-demand and on-site synthesis, which leads to less energy for transportation and easy recycling of substances.

How easy are the syntheses of allenes?

This short review highlights some of the recent important developments on the synthesis of allenes and its applications on the synthesis of some allenic natural products and allenic-based optoelectronic materials.

Generation and reaction of cyano-substituted aryllithium compounds using microreactors

We developed a microflow method for the generation and reactions of aryllithiums bearing a cyano group, including o-lithiobenzonitrile, m-lithiobenzonitrile and p-lithiobenzonitrile. The method was effective at much higher temperatures than are required for conventional macrobatch reactions, by virtue of rapid mixing, short residence time, and efficient temperature control. In addition, reactions of o-lithiobenzonitrile with carbonyl compounds followed by trapping of the resulting lithium alkoxides with electrophiles were achieved in an integrated microflow system.

Acid-mediated reactions under microfluidic conditions: a new strategy for practical synthesis of biofunctional natural products

Microfluidic conditions were applied to acid-mediated reactions, namely, glycosylation, reductive opening of the benzylidene acetal groups, and dehydration, which are the keys to the practical synthesis of N-glycans and the immunostimulating natural product, pristane. A distinctly different reactivity from that in conventional batch stirring was found; the vigorous micromixing of the reactants with the concentrated acids is critical especially for the "fast" reactions to be successful. Such a common feature might be due to the integration of all favorable aspects of microfluidic conditions, i.e., efficient mixing, precise temperature control, and the easy handling of the reactive intermediate by controlling the residence time. The microfluidic reactions cited in this review indicate the need to reinvestigate the traditional or imaginary reactions which have so far been performed and evaluated only in batch apparatus, and therefore they could be recognized as a new strategy in synthesizing natural products of prominent biological activity in a "practical" and a "industrial" manner.

Synthesis of unsymmetrically substituted biaryls via sequential lithiation of dibromobiaryls using integrated microflow systems

A microflow system consisting of micromixers and microtube reactors provides an effective method for the introduction of two electrophiles onto dibromobiaryls. Selective monolithiation of dibromobiaryls, such as 2,2′-dibromobiphenyl, 4,4′-dibromobiphenyl, 2,7-dibromo-9,9-dioctylfluorene, 2,2′-dibromo-1,1′-binaphthyl, and 2,2′-dibromobibenzyl with 1 equiv of n-butyllithium followed by the reaction with electrophiles was achieved using a microflow system by virtue of fast micromixing and precise temperature control. Sequential introduction of two different electrophiles was achieved using an integrated microflow system composed of four micromixers and four microtube reactors to obtain unsymmetrically substituted biaryl compounds.