Diastereoselective [3 + 2] vs [4 + 2] Cycloadditions of Nitroprolinates with α,β-Unsaturated Aldehydes and Electrophilic Alkenes: An Example of Total Periselectivity
Diastereoselective multicomponent reactions of enantioenriched 4-nitroprolinates, obtained by enantiocatalyzed 1,3-dipolar cycloaddition (1,3-DC) of imino esters and nitroalkenes, with α,β-unsaturated aldehydes and electrophilic alkenes proceed with total periselectivity depending on the structure o...
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Published in | Journal of organic chemistry Vol. 82; no. 12; pp. 6298 - 6312 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
WASHINGTON
American Chemical Society
16.06.2017
Amer Chemical Soc |
Subjects | |
Online Access | Get full text |
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Summary: | Diastereoselective multicomponent reactions of enantioenriched 4-nitroprolinates, obtained by enantiocatalyzed 1,3-dipolar cycloaddition (1,3-DC) of imino esters and nitroalkenes, with α,β-unsaturated aldehydes and electrophilic alkenes proceed with total periselectivity depending on the structure of the aldehyde employed. This process evolves through a [3 + 2] 1,3-DC when cinnamaldehyde is used in the presence of an azomethine ylide, giving the corresponding highly substituted pyrrolizidines with endo selectivity. However, in the case of the α,β-unsaturated aldehyde, which contains a hydrogen atom at the γ position, an amine–aldehyde–dienophile (AAD) [4 + 2] cycloaddition takes place by formation of an intermediate 1-amino-1,3-diene, affording highly functionalized cyclohexenes with high endo diastereoselectivity. This AAD process only occurred when a nitro group is bonded to the 4-position of the initial enantiomerically enriched pyrrolidine ring. DFT calculations have been carried out with the aim of explaining this different behavior between pyrrolidines with or without a nitro group, demonstrating the strong nitro-group-dependent periselectivity. The results of these computational studies also support the experimentally obtained absolute configuration of the final adducts. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3263 1520-6904 |
DOI: | 10.1021/acs.joc.7b00903 |