Chiral cyclopropenyl ketones: reactive and selective Diels-Alder dienophiles.

The synthesis and Diels–Alder reactions of cyclopropenyl ketones are described. Cyclopropenyl ketones are highly reactive dienophiles that can engage a range of cyclic dienes and 2,3-dimethylbutadiene. The strategy of using cyclopropenyl ketones to facilitate Diels–Alder reactions is not limited to products that contain three-membered rings, as reductive opening by SmI2 can be used to produce a product that lacks a cyclopropane but retains a quaternary stereogenic center.