Mannich sulfonyl imine

Scheme 10.34 Cu-catalysed Mannich-type reactions of A -sulfonyl imines with Fes-ulphos ligand.

Carretero and coworkers have successfully employed a copper(I)-Fesulphos complex as a Lewis acid for enantioselective Mannich-type reactions of N-sulfonyl imines [43]. A combination of [151 CuBr]2 and AgCl04 does efficiently catalyze the addition of silyl enol ethers of ketones, esters, and thioesters (150) to N-(2-thienyl)sulfonyl aldimines (Scheme 17.30). The corresponding P-amino carbonyl derivatives (152) were isolated in good yields with generally good enan-tioselectivity. 

In 2009, Feng and coworkers developed new guanidine catalysts with an amino amide skeleton [139]. Among the various catalysts tested, guanidine 49 was found to be the most active for the enantioselective Michael reaction of a (i-ketoester with nitroolefins (Scheme 10.46). The conjugate addition products were obtained in high yields and excellent diastereo- and enantioselectivities. The same researchers used bis-guanidine catalysts for the enantioselective inverse-electron-demand hetero-Diels-Alder reaction of chalcones with azlactones (Scheme 10.47) [140] and enantioselective Mannich-type reaction of a-isothiocyanato imide and sulfonyl imines (Scheme 10.48) [141]. 

Scheme 10.48 Mannich-type reaction of Ot-isothiocyanato imide and sulfonyl imines.

In 2007, Ooi and coworkers introduced chiral tetraaminophosphonium salts as a new class of Bronsted acids [166]. Similar to the guanidine/guanidinium case, these tetraaminophosphonium salts act as Bronsted bases in their neutral/ deprotonated (triaminoiminophosphorane) form, while they can also be used as mono-functional Bronsted acids in their protonated, phosphonium form. Phos-phonium salt 67, when neutralized in situ with KO Bu, was shown to be a highly effective catalyst in the enantioselective Henry reaction of nitroalkanes with various aromatic and aliphatic aldehydes (Scheme 10.65). The same strategy was further applied to the catalytic asymmetric Henry reaction of ynals [167] and hydrophosphonylation of ynones (Scheme 10.66) [168]. Brfunctional catalysis using this scaffold were also obtained using the carboxylate salts of tetraaminophosphoniums in the direct Mannich reaction of sulfonyl imines with azlactones (Scheme 10.67) [169]. 

Scheme 10.67 Enantioselective Mannich reaction of sulfonyl imines with aziactones.

Newly designed chiral tetraaminophosphonium salt 184 possessing an organic anion cooperatively catalyzes asymmetric Mannich-type reaction of azlactones (182) with N-sulfonyl imines (183) (Scheme 28.20). The basic carboxylate anion deprotonates the active methine proton of the azlactone (182) to form the corresponding chiral phosphonium enolate with a defined hydrogen bonding network (ion pair), and then highly stereoselective bond formation proceeds [92]. 

Mannich reaction 279 N-sulfonyl imines 187 sulfonylated prolinamide 623 sulfonylation 1256 -asymmetric 1257 P-sulfonyl acetonitrile 867 N-sulfonyl imines 862 sulfoxides 389,1256... 

In recent years, catalytic asymmetric Mukaiyama aldol reactions have emerged as one of the most important C—C bond-forming reactions [35]. Among the various types of chiral Lewis acid catalysts used for the Mukaiyama aldol reactions, chirally modified boron derived from N-sulfonyl-fS)-tryptophan was effective for the reaction between aldehyde and silyl enol ether [36, 37]. By using polymer-supported N-sulfonyl-fS)-tryptophan synthesized by polymerization of the chiral monomer, the polymeric version of Yamamoto s oxazaborohdinone catalyst was prepared by treatment with 3,5-bis(trifluoromethyl)phenyl boron dichloride ]38]. The polymeric chiral Lewis acid catalyst 55 worked well in the asymmetric aldol reaction of benzaldehyde with silyl enol ether derived from acetophenone to give [i-hydroxyketone with up to 95% ee, as shown in Scheme 3.16. In addition to the Mukaiyama aldol reaction, a Mannich-type reaction and an allylation reaction of imine 58 were also asymmetrically catalyzed by the same polymeric catalyst ]38]. 

The reversibility problem in 1,2-additions is alleviated when imines bearing an electron-poor protecting group at nitrogen (sulfonyl, aeyl, ear-bamoyl) are employed as aeceptor partners, rendering possible even the use of 1,3-dicarbonyl compounds as donors. For example, Sehaus and eoworkers reported the highly enantioselective Mannich reaction of acetoacetates and cyclic 1,3-dicarbonyl compounds with N-carbamoyl imines derived from benzaldehydes and cinnamaldehydes catalysed by the natural Cinchona alkaloid cinchonine (CN) (Scheme 14.15). On the basis of the obtained results they developed a model that accounts for the observed diastereo- and enantioselectivity based on the bifunctional nature of the catalyst, which acts simultaneously as a hydrogen-bond donor and acceptor. 

To prepare for the intramolecular Mannich condensation, the azide was reduced to give the imine, and the methyl ketone was converted to the silyl enol ether. Under Lewis acid conditions, the sulfonyl group imderwent an imanticipated 1,3-migration, to give 11. 

An efficient asymmetric Mannich-type reaction of ct-cyano-a-sulfonyl carbanions has been achieved by exploiting the structural modularity and anion recognition ability of chiral 1,2,3-triazolium ions (7). This protocol has proved to be applicable to a variety of A-Boc imines and cyanosulfones, affording -amino-a-cyanosulfones in excellent yields with high stereoselectivities. 

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