Flash chemistry Ultra-fast microflow synthesis

The efficiency of an organic synthesis reaction is essentially characterized by the yield of the desired product, ideally 100%. This value implies not only the complete consumption of the starting reagents, but also the orientation of the conversion towards a single product among several possible transformations (competitive reactions): the selectivity of the reaction. In the case of very fast reactions (< 1 min), the speed of the reaction mixture becomes an important parameter which strongly influences the fate of successive competitive processes, and kinetic rules, valid only in homogeneous media, are no longer applicable to inefficient mixtures. Continuous-flow microreactor synthesis technology offers undeniable advantages for controlling very fast reactions with high selectivity, excellent material and heat transfer and extremely precise reaction times (residence times in the microreactor). This article presents the effects of miniaturizing continuous-flow reactors to achieve very short reaction times (a few milliseconds, hence the term "flash chemistry") and highly efficient mixtures to carry out organic chemistry reactions "impossible" by conventional means of synthesis, and pave the way for new molecules of varied interest. This article is illustrated by examples from organolithium chemistry, and also by historical cases of masked selectivity (ester reductions, amine alkylations...).