Michael Addition Reaction Involving Nitroalkenes

The low catalyst loading (as low as 0.1mol%) demonstrated the remarkably high catalytic activity of squaramide catalyst 13. This work estabhshed the squaramide unit as an effective scaffold on which to build chiral H-bond donor catalysts. 

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The mechanism is presumed to involve a pathway related to those proposed for other base-catalyzed reactions of isocyanoacetates with Michael acceptors. Thus base-induced formation of enolate 9 is followed by Michael addition to the nitroalkene and cyclization of nitronate 10 to furnish 11 after protonation. Loss of nitrous acid and aromatization affords pyrrole ester 12. 

In a completely different context, a cascade Michael/intramolecular addition process involving nitroalkenes and isocyanoesters has been developed, which results in a formal [3 -I- 2] cycloaddition reaction and therefore consisting of a direct and very efficient methodology for the asymmetric synthesis of 2,3-dihydropyrroles (Scheme 7.70). ° The reaction was catalyzed by cinchona... 

Yosikoshi reported the synthesis of furan derivatives by the reaction of 1,3-diketones with nitroalkenes, in which the Michael addition of the anions of 1,3-diketones and the subsequent intramolecular displacement of the nitro group by enolate oxygen are involved as key steps (Eq. 7.40).42... 

The reaction involves the amine-catalyzed conversion of an aldehyde into a nitroalkene by reaction with nitromethane followed by a transition-metal-catalyzed Michael addition of p-dicarbonyl compounds in the same reaction vessel. Typically, amine catalysts and nickel complexes are incompatible due to their tendency to chelate and to render each other inactive. However, microencapsulation of poly(ethyleneimine) (PEI) forms catalyst 140, which can successfully be used in tandem with the nickel-based catalyst 141 (Figure 3.6). 

Despite of the fact that Baylis and Hillman reported the synthesis of a-hydr-oxyethylated nitroethylene through the reaction between nitroethylene and acetaldehyde in the presence of DABCO, nitroalkenes employed as activated olefins in MBH reaction have not received much attention until recently. Prompted by the fact that nitroalkenes have shown superior Michael acceptor abilities, and that the first step in the MBH reaction is the Michael-type addition of the catalyst to substrate, Namboothiri et al. have published a series of papers on nitroalkenes involved the MBH reaction. The MBH reactions between nitroalkenes and various electrophiles such as formaldehyde, activated carbonyl compounds, imines, alkenes and azodicarboxylates " in the presence... 

Finally, a remarkable four-component tandem Michael-aza-Henry-hemi-aminalisation-dehydration tandem reaction was recently developed by Lin and co-workers on the basis of a dual organocatalysis involving a chiral diaryl prolinol trimethylsilyl ether and a chiral cinchona alkaloid." As shown in Scheme 2.37, the reaction began with the Michael addition of an aldehyde to a nitroalkene catalysed by the L-proline-derived catalyst, giving the corresponding intermediate aldehyde. The latter intermediate... 

Cyclopropanecarboxylic esters have been prepared, in 75—86 % yield, by intramolecular alkylation of 4-chloroalkyl esters, using phase-transfer catalysis. Monoalkylation of nitro-alkenes by acrylic esters occurs in a controlled manner if a two-phase system is used, to give products of Michael addition in 45—65 % yield for five examples. An interesting variant on this reaction involves the generation of the a-nitro-carbanion by conjugate reduction of a nitroalkene with sodium borohydride followed by its conjugate addition to methyl acrylate yields of 62—95% are reported for five cases (Scheme 39). ... 

All of these reactions proceed in a similar pathway which involves the Michael type additions of enamines to nitroalkenes or addition of nitroalkanes to imines and cyclization. This process has been achieved by solid-phase variation (Scheme 10.2).14... 

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