Diketopiperazines as Catalysts for the Strecker Reaction

Inspired from the usage of cyclic peptides for the hydrocyanation of carbonyls, cycHc peptides were applied to the Strecker reaction (Table 30.3) [12, 13]. Employment of 2 to the mechanistically similar Strecker reachon did not provide any asymmetric introduction In the reachon of benzaldehyde (1) catalyzed by 2, proton transfer takes place from HCN to the imidazole residue in 2. The resulhng imidazoHum ion can serve as an acid catalyst for the asymmetric cyanahon of 1 meanwhile, in the case of the Strecker reachon, the more basic benzaldimine (17) becomes protonated direchy by HCN without interachon with the catalyst [4]. Thus, replacement of the imidazole funchon with the more basic guarhdine turned 

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