Diastereoselective [3 + 2] vs [4 + 2] Cycloadditions of Nitroprolinates with α,β-Unsaturated Aldehydes and Electrophilic Alkenes: An Example of Total Periselectivity
- Selva, Verónica
- Larrañaga Agirre, Olatz
- Castelló Moncayo, Luis Miguel
- Nájera, Carmen
- Sansano, Jose M.
- Cózar Ruano, Abel de
DOIAbstract
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, affor...