Reactions of Achiral Dienophiles with Chiral Dienes

2 Reactions of Achiral Dienophiles with Chiral Dienes 

Non-catalyzed Diels-Alder reactions of chiral dienes with the achiral dienophiles compiled below have been widely studied. As dienophiles especially quinones (1), maleic anhydride (2), nitro-substituted alkenes (5) and acrylates (4) have been examined. 

Moderate selectivities were observed in non-catalyzed cycloaddition reactions of chiral pentadienoic acid esters and amides with e.g. benzoquinone even at higher temperature and at high pressure (1 lO torr). 

Thermal cycloaddition reactions of chiral 1-acyloxy-1,3-butadienes derived from chiral carboxylic acids vith electron-deficient alkenes, e.g. A -ethylmaleimide or quinones, were found to be highly endo selective. Moderate to high diastereoselectivities were obtained ( 96 4). 

Asyirumetric thermal cycloadditions of alkoxydienes with a variety of dienophiles (1,2,3,6), e.g, benzoquinone (1), tetracyanoethylene or maleic anhydride, lead veiy selectively to the cycloadducts.  

---