Nitroalkanes Michael additions, sulfones

In 2009, Zhu and Lu reported organocatalytic asymmetric Michael additions of nitroalkanes to another Michael acceptor such as vinyl sulfone mediated by another cinchona alkaloid-derived thiourea catalyst, which afforded the desired Michael products with good enantioselectivities of up to 84% ee (Scheme 1.20). This method in combination with a ready desulfonation represented a new approach to access a-alkylated chiral amines. 

Scheme 1.20 Michael additions of nitroalkanes to vinyl sulfone catalysed by cinchona alkaloid-derived thiourea.

Various thiourea-based bifunctional organocatalysts (e.g. 289a and 372a,b) have been successfully applied for the Michael addition of nitroalkanes RCH2NO2 to 3-ylidene oxindoles (373). The resulting enolate intermediates (374) were then trapped by electrophiles, such as enones, maleimide, and sulfone CH2=C(S02Ph)2. The products were obtained with <99% ee and >95 5... 

SCHEME 2231. Organo-catalyzed asymmetric Michael additions of nitroalkanes (A) and aldehydes (B) to a,(3-unsaturated sulfones. 

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