β-Chloroaldehydes from Trapping Zirconium Enolates Produced in Asymmetric 1,4-Additions.

Zirconium enolates, derived from copper-catalyzed asymmetric conjugate additions, are trapped with the Vilsmeier-Haack reagent. Asymmetric additions generate quaternary carbon centers with high enantioselectivity (generally ∼90% ee), and the enolates are converted to unsaturated β-chloroaldehydes (41-57% yields). The reaction tolerates changes to the nucleophile, can be used to form five-, six-, or seven-membered ring products, and is scalable to 5 mmol, and the products are readily elaborated by condensation, cross coupling, and addition reactions.