Organocatalysts biocatalysts

Even considering only the example of the proline family of aldol catalysts, it is dear that there will soon be hundreds of cases of organocatalysts described in the literature. Direct, organocatalytic aldol reactions do not yet have the generality of traditional stoichiometric methods, which can offer predictable results for a wide variety of substrates. However, companies already offer to screen substrates against panels of up to 200 enzymes to find the optimum biocatalyst for a reaction, and the same approach could be applied to identify rapidly the best organocatalyst for a process. 

Referring to a mechanistic classification of organocatalysts (Seayad and List 2005), currently the two most prominent classes are Brpnsted acid catalysts and Lewis base catalysts. Within the latter class chiral secondary amines (enamine, iminium, dienamine activation for a short review please refer to List 2006) play an important role and can be considered as—by now—already widely extended mimetics of type I aldolases, whereas acylation catalysts, for example, refer to hydrolases or peptidases (Spivey and McDaid 2007). Thiamine-dependent enzymes, a versatile class of C-C bond forming and destructing biocatalysts (Pohl et al. 2002) with their common catalytically active coenzyme thiamine (vitamin Bi), are understood to be the biomimetic roots ofcar-bene catalysis, a further class of nucleophilic, Lewis base catalysis with increasing importance in the last 5 years. 

Combinations of gold with other transition metals, organocatalysts, or biocatalysts in tandem transformations... 

Undoubtedly, both biocatalysts [2] and organocatalysts [3] offer a greener alternative and compare well with their alter ego metal-based catalysts, since they display a high stereoselectivity on a wide range of substrates under much milder conditions. 

The selective oxidation of sulfides and amines to sulfoxide and amine oxides can be obtained with a variety of oxidants. In particular, catalytic oxidations employing environmentally benign oxidants such as hydrogen peroxide and molecular oxygen have attracted considerable interest recently. A number of catalytic methods that give highly selective and mildly selective oxidations with the latter oxidants are known today. Organocatalysts (e. g., flavins), biocatalysts and metal catalysts have been used for these transformations. 

---