Thiourea derived catalysts oxidation

Asymmetric cyanohydrin synthesis remains an important reaction for organocatalysis and many of the catalyst classes discussed in subsequent chapters give highly effective catalysts for this reaction. These include Cinchona alkaloid derivatives, thioureas, guanidines, amine-oxides, diols and diamines. 

Chiral oxazaborolidinium ion is an excellent catalyst for the cyanosilylation of methyl ketones promoted by cyanotrimethylsilane and diphenylmethyl phosphine oxide (eq 27). Chiral thiourea (eq 28) and amino acid salt (eq 29) have been developed and employed as catalysts in the enantioselective s)m-thesis of cyanohydrins and their derivatives. 

New cinchona derivatives are continuously being developed for appUcation in asymmetric organocatalysis. Examples of catalysts obtained by further modification of existing derivatives include an N-oxide of dihydrocupreidine [127], a C6 -N-Boc-glycine-P-isocupreine (53) [128], a C9 thiourea substituted at a remote site with a sulfonamide group (54) [129, 130], and catalysts with an amine as well as a thiourea group (55) [131] (Figure 6.16). 

Ye, Liang, and coworkers reported the addition of diphenylphosphine oxide to enones catalyzed by a bifunctional primary amine thiourea catalyst (127) derived from cinchona alkaloid (Scheme 33.38) [119], Cyclic and acyclic enones react with phosphine oxides under the optimized conditions to furnish the phosphine derivatives 128 in excellent yields and enantioselectivities. The primary amine of the catalyst activates the enone via an iminium, while the thiourea moiety activates and directs the phosphine group. 

Hydroxylations of fatty acids by cytochrome P450119 compound increase in rate with chain length and show no intermolecular KE in buffer. With glycerol, the rate of reaction of lauric acid increases, and a KIE is observed. Reversible formation of a non-reactive complex of a fatty acid with the cytochrome and its isomerization to a reactive one is proposed. A tandem oxidative cyclocondensation process is reported for the synthesis of 3,4-dihydropyrimidin-2(l//)-one or -thione derivatives from primary aryl alcohols, -keto esters, and urea or thiourea in the presence of aluminium nitrate nonahydrate as oxidant catalyst. ... 

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