Squaramides asymmetric Michael additions

Xn et al. have carried ont asymmetric Michael addition reaction in ball mill using squaramide catalyst (Scheme 2.32) [23]. Optimal reaction conditions in planetary ball mill feature milling of 1,3-diones 83 and aryl styrenes in the presence of the cinchona-derived squaramide catalyst CA (5mol%). In these conditions, high yields... 

Scheme 21.32 Squaramides as an organocatalyst for asymmetric Michael additions.

A chiral quinine-derived squaramide catalysed the highly enantioselective Michael addition of malononitrile to chalcones. The reactions take place at a very low catalyst loading (0.5 mol%) and provide the Michael adducts with high yields and good enan-tioselectivities (up to 96% ee). Chiral bifunctional squaramides have also been used as multiple hydrogen-bond donor-acceptor organocatalysts for the asymmetric Michael addition of nitroolefins to 1,3-dicarbonyl compounds. ... 

Polysubstituted 3,4-dihydro-3-nitro-2ff-chromans are obtained from the enantioselective Michael—Michael cascade reaction of chalcone enolates and nitromethane catalyzed by bifunctional thiourea 19 (Scheme 31) (13JOC6488) and tandem Friedel—Crafts alkylation—Michael addition reaction of nitroolefin enoates and 1-methylindole promoted by Zn(OTf)2 (13S601).A squaramide-tertiary amine catalyst promotes the asymmetric sulfa-Michael—Michael cascade reaction of thiosalicylates with nitroalkene enoates which leads to polysubstituted chromans in high yields with excellent stereoselectivities (13OL1190). 

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