Hydrogen chiral guanidine catalysts

Some bifunctional hydrogen-bond donor/Brpnsted base catalysts are shown in Figures 2.39 and 2.40. They comprise chiral amino alcohols and amino phenols, chiral amine-thiourea derivatives, and chiral guanidines, among others. In the absence of detailed experimental NMR or kinetic studies [179], most of our... 

Ooi has recently reported application of chiral P-spiro tetraaminophosphonium salt 37 as a catalyst for the highly enantio- and diasterioselective direct Henry reaction of a variety of aliphatic and aromatic aldehydes with nitroalkanes (Scheme 5.51) [92]. Addihon of the strong base KO Bu generates in situ the corresponding catalyhcally active triaminoiminophosphorane base A. Ensuing formation of a doubly hydrogen-bonded ion pair B positions the nitronate for stereoselective addition to the aldehyde. This catalyst system bears many similarities to guanidine base catalysis. 

Corey and Grogan recently developed a novel catalytic enantioselective Strecker reaction which utilized the readily available chiral C2-symmetric guanidine 19 as a bifunc-tional catalyst [12], The addition of hydrogen cyanide to achiral aromatic and aliphatic N-benzhydrylimines 18 gave N-benzhydryl-a-aminonitriles 20 (Scheme 7), which were readily converted to the corresponding amino acids with 6 N HCI. The use of N-benzyl- or N-fluorenylimines afforded products of poor enantiomeric purity. 

Chiral primary amine-guanidines have been employed as organocatalysts in Michael addition of aldehydes to maleimides that gave succinimides in <96% ee. DFT and M06-2X calculations suggest the hydrogen bonding between the maleimide C=0 and the catalyst NH groups. ... 

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