This strategy offers many benefits including operational simplicity, yet it is more challenging as substrates employed must possess functional groups of similar properties, thus resulting in competitive reaction pathways. Therefore, such catalytic activation can be referred to as differentiating catalysis. (4) In this type of approach, electronic properties of substrates are enhanced and at the same time differentiated via the formation of both LUMO-lowered and HOMO-raised reactive intermediates.
(3) On the contrary, the pathway relying on the activation of both substrates by two molecules of the same catalyst is much less explored. The main tool used for this type of asymmetric synthesis is synergistic catalysis where two different catalysts independently activate two substrates, thus providing chiral intermediates capable of participating in a given transformation. A much easier strategy is based on the catalytic generation of chiral intermediates that participate in the reaction as no additional synthetic protocols are required. The main drawback of the approach concerns its atom- and step-economy as chiral auxiliaries are used in stoichiometric amounts and must be introduced and removed in additional, time-consuming procedures. When appropriate enantiomers of substrates are employed (“match” case), the chirality of both reagents synergistically enhances the stereochemical reaction outcome ( Scheme 1). (2) It leads to the formation of a new stereogenic center by the utilization of two enantiopure substrates bearing a chiral auxiliary unit. (1) Within this area of research, double-asymmetric synthesis constitutes an interesting approach. Stereocontrolled synthesis of specific structural motifs is one of the most important tasks in contemporary organic chemistry.
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