Intermolecular Michael Additions of Other-than-C-Nucleophiles

5 Intermolecular Michael Additions of Other-than-C-Nucleophiles 

In 2009, Enders and Hoffman explored the reactivity of a,(3-unsaturated sulfonates and aromatic thiols in sulfa-Michael additions. When the reactions were catalysed by a chiral bifunctional thiourea derived from quinine, the sulfa-Michael adducts were formed in moderate enantioseleetivities of up to 64% ee, albeit with generally good yields, as shown in Seheme 1.70. 

A chiral bicyclic guanidine derivative was employed as an organocatalyst for the sulfa-Miehael addition of thiols to tert- mty 2-phthalimido acrylates by Tan et ah, providing the expected chiral Michael adducts in excellent yields and enantioselectivities of up to 92% ee, as shown in Seheme 1.71.  

In addition, Shimizu et al. have applied novel multifunetional inherently chiral calix[4]arene to the sulfa-Michael addition of thiols to cyclohexenone. The expected Michael adducts were obtained in generally excellent yields (18-99%) but with low enantioselectivities ( 25% ee). The reaction system was also applied to other cyclic and acyclic enones, providing the corresponding products with a comparable degree of enantioselectivity to that obtained with cyclohexenone. 

In addition, Cordova et al. have developed highly enantioselective organocatalytic hydrophosphination reactions of a,p-unsaturated aldehydes. These novel reactions were catalysed by protected chiral diarylprolinol derivatives 

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