Diastereoselective syntheses of chroman spiroketals via [4 + 2] cycloaddition of enol ethers and o-quinone methides

A variety of chroman spiroketals are synthesized via inverse-demand [4 + 2] cycloaddition of enol ethers and ortho-quinone methides (o-QMs). Low temperature o-QM generation in situ allows for the kinetic, diastereoselective construction of these motifs, providing entry to a number of unusual chroman spiroketal natural products.