Dienamines acylation

The acylation of dienamines has not been extensively investigated. The dienamine (127) prepared by Birch reduction of N,N-dimethyl-p-toluidine has been shown to react with diketene (90) to give the chromone (128), showing that attack occurs at the /9-carbon of the dienamine system. 

A general synthesis of C-alkyl-dehydroberberines (88) by acid-catalysed cyclization of acyl-dienamines (87) is the subject of a recent patent.96 The synthesis... 

Surprisingly little work appears to have been published on the acylation of dienamines. Annulations which may be effected with a,/ -unsaturated acid chlorides and diketene are discussed in Sections VII.C and VIII.C, respectively. 

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. 

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