Reactions of 2-Aza-l,3-dienes

Asymmetric Lewis acid-catalyzed hetero Diels-Alder reactions of 2-aza-1,3-dienes have been studied for isolated cases. Highly selective thermal cycloadditions have been observed in the reactions of chiral, halogenated 2-aza-1,3-dienes with acyclic diazo compounds conducted at 80°C.  

Reactions of 2-aza-l,3-butadienes with electron-donating substituents and chiral nitroso compounds take place selectively in the absence of Lewis acids at low temperature. The cycloadducts are useful precursors of a-amino acids. 

Isoquinolinium salts represent 2-aza-1,3-butadienes activated by A-arylation. Highly stereoselective cycloadditions with chiral enolethers have been reported leading to enantiomerically pure functionalized tetralines in high yields. 

Reactions of Chiral N-Acyl-Itnines as Dienes with Achiral Enamines or Alkenes 

Reactions of//-acylimines with electron-rich alkenes furnish 5,6-dihydro-l,3-oxazines. Low to moderate diastereoselectivities were observed for the combination of chiral N-acylimines and achiral enamines, Highly selective reactions are observed in cycloadditions of chiral enamines with achiral dienes as well as with chiral dienes in the case of a matched pair. 

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The Lewis acid-mediated reactions of 2-aza-l,3-dienes and aldehydes, resulting in tetrahydro-l,3-oxazin-4-one derivatives, were explained in terms of the competitive existence of two reaction pathways a [4+2] hetero-Diels-Alder cycloaddition reaction and a Mukaiyama aldol reaction <2001TA439>. 

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