Catalytic Asymmetric [4+2]-Cycloaddition of Dienes with Aldehydes

Despite its significant
potential, a general catalytic asymmetric
[4+2]-cycloaddition of simple and electronically unbiased dienes with
any type of aldehyde has long been unknown. Previously developed methodologies
invariably require activated, electronically engineered substrates.
We now provide a general solution to this problem. We show that highly
acidic and confined imidodiphosphorimidates (IDPis) are extremely
effective Brønsted acid catalysts of the hetero-Diels–Alder
reaction of a wide variety of aldehydes and dienes to give enantiomerically
enriched dihydropyrans. Excellent stereoselectivity is generally observed
and a variety of scents and natural products can be easily accessed.