2008
DOI: 10.1021/ja800345r
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Enantioselective Organocatalytic Michael Addition of Aldehydes to Nitroethylene: Efficient Access to γ2-Amino Acids

Abstract: The development of asymmetric conjugate addition reactions for C-C bond formation remains an important challenge in organic synthesis. 1,2 Much recent work has focused on organocatalytic Michael addition of carbonyl compounds to nitroalkenes. [3][4][5] Among these reactions, Michael addition of aldehydes to nitroalkenes is of particular interest because of the valuable synthetic intermediates that are generated. 4 β-Aryl nitroalkenes have been the most common Michael acceptors for reactions developed by other … Show more

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Cited by 171 publications
(48 citation statements)
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“…[4,5] The behaviour of these catalysts is significant, but the method holds important limitations with regards to substrate scope and enantioselectivity: a large excess (10 equivalents) of the aldehyde is usually required and modest selectivities (typically 70 % ee) are obtained. On the other hand, while the direct catalytic and asymmetric 1,4-addition of aldehydes to certain electron-deficient olefins, [6,7] most particularly nitroolefins, [7,8] have met success recently, one accompanying problem to the reaction with vinyl sulfone acceptors is the retroaddition, which causes formation of undesired dimeric side products. [3] Herein we report the use of less basic chiral amine catalysts (see Figure 1) to provide a solution to these problems thus considerably expanding the utility of vinyl sulfones in organic synthesis.…”
mentioning
confidence: 99%
“…[4,5] The behaviour of these catalysts is significant, but the method holds important limitations with regards to substrate scope and enantioselectivity: a large excess (10 equivalents) of the aldehyde is usually required and modest selectivities (typically 70 % ee) are obtained. On the other hand, while the direct catalytic and asymmetric 1,4-addition of aldehydes to certain electron-deficient olefins, [6,7] most particularly nitroolefins, [7,8] have met success recently, one accompanying problem to the reaction with vinyl sulfone acceptors is the retroaddition, which causes formation of undesired dimeric side products. [3] Herein we report the use of less basic chiral amine catalysts (see Figure 1) to provide a solution to these problems thus considerably expanding the utility of vinyl sulfones in organic synthesis.…”
mentioning
confidence: 99%
“…8g; 19 Thus, the addition of benzoic acid (20 mol%) resulted in a slight improvement of yield and enantioselectivity compared to when no additive was used (Table 1, compare entries 5 and 12). This positive result prompted us to explore if a modulation of the pKa of the additive by changing the substituent in the aromatic ring could be beneficial.…”
Section: Resultsmentioning
confidence: 96%
“…Synthetic routes to multiply substituted chiral b and c amino acids have been developed. 12 For purposes of exploring conformational space it is advantageous to employ readily available achiral, substituted b and c residues. The use of symmetrical, geminal disubstitution is a device that has proved extremely successful in the generation of well defined, folded peptides in a amino acid sequences.…”
Section: -11mentioning
confidence: 99%