Dihapto-Coordination of the Diene to Promote Sluggish Diels-Alder Reactions

Significance

The Diels-Alder reaction is one of the most studied reactions throughout organic chemistry. The authors of this paper devised a way to increase the reactivity of an unreactive diene (1,3-cyclohexadiene) by using a π-base-promoting transition-metal complex. The cyclohexadiene-Mo complex was prepared in a 1.5:1 diastereomeric ratio. Although this diene was unable to react directly with the ethylvinyl ketone, the use of a Lewis acid (BF₃·OEt₂) afforded the desired cycloadduct, which still contained a η²-complex. This complex could be oxidized and the desired product was released by either the introduction of air to the system or by addition of AgOTf.