Switchable Diastereoselectivity in Enantioselective [4+2] Cycloadditions with Simple Olefins by Asymmetric Binary Acid Catalysis

摘要

Chiral 3,4-dihydro-2H-pyrans and tetrahydropyrans are versatile structural motifs of a number of bioactive natural products (e.g. epicalyxinF and sugiresinol), fragrances (doremox), and foodstuff flavorings (Figure 1). A straight- forward approach to access this type of products is the catalytic asymmetric inverse-electron-demand Diels-Alder reaction between α,β-unsaturated carbonyl compounds and alkenes. Though extensively explored in asymmetric catalysis, this reaction has been limited to electron-rich alkenes, such as enol ethers, enamines, and cyclopenta-dieries. Reactions with electronically unbiased simple alkenes would give the illustrated compounds directly (Figure 1), but have been rather unsuccessful.