Conjugate Addition of Carbon-Centered Nucleophiles

The Michael addidon of nitroalkanes to nitroalkenes is catalyzed by triethylamine to give 1,3-dirutro compounds fEq. 4.45. In some cases, the intramolecular displacement of thenitro group takes place to give cyclic nitronates fEq. 4.46.  

The dsymmetnc Michael dclcliQon of 1,3-chcdrbonyl compounds to nitrostyrene is promoted by chiriil alkaloid catalysts to give the addition products in good chemical yield, but the enandoselecdvity is rather low fEq 4 47  

3b Enolates Derived From Ketones and Esters and Carbanions Stabilized by Sulfur In recent years, a variety of procedures for the snccessfid addidon of simple ketones or esters to nitroalkenes have been developed. Seebach and coworkers have reported 

Pyroglntamic acid is a useful starting material for the synthesis of several naniral products, such as pyrtolidme alkaloids, kainoids, and other unnaniral amino acids. Interesting chemose-lecdve Michael additions of anions derived from pyroglntamates have been reported fsee Eqs. 4.54 and4.55.  

A short synthesis of ptostaglandm derivatives via a three component coupling reaction reported, in which the enolates are trapped v/ith nitroalkenes. The nitro group is removed v 

3a Active Methylene Compounds Nitroalkenes are powerful Michael acceptors that can serve as synthons of the type +C-C-NH2 and +C-(C=0)R. Classically, the reactions of nitroalkenes with carbon-centered nucleophiles have been limited to reactions carried out under mildly basic conditions using relatively acidic reaction partners such as malonate derivatives and 1,3-diketones.56 The Michael addition of such active methylene compounds to nitroalkenes is catalyzed by various bases, including ROM (M = metal), triton B, and triethylamine. For example, the reaction of acetyl acetone or ethyl acetate with nitrostyrene proceeds in the presence of catalytic amounts of triethylamine at room temperature to give the adduct in 98% or 78% yield, respectively. The addition products are useful intermediates for the preparation of furans or pyrroles.57 Metal complex catalysts such as Ni(acac)2 are also effective to induce the Michael addition of acetyl acetone to nitrostyrene. Yoshikoshi and coworkers have found that the potassium fluoride-catalyzed addition of 1,3-dicarbonyl compounds to nitroalkenes leads to the formation of furans (Eq. 4.42) or Michael adducts and their Nef products (Eqs. 4.43 and 4.44), depending on substrates and conditions.59 

Dianions or trianions derived from 1,3-dicarbonyl compounds react with nitroalkenes at low temperature to give the adduct, which undergoes a nitro-aldol type cyclization (Eq. 4.50).640 

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