Reaction of dianions of acyclic β-enamino ketones with electrophiles. Part 2. Oxiranes: synthesis of γ′- and ε-hydroxy-β-enamino ketones and of α-tetrahydrofurylidene ketones

Abstract

β-Monoalkylamino α,β-unsaturated ketones can be regioselectively dimetallated either at the α′- or in the γ-positions. The reaction of the resulting dianions with oxiranes proceeds in good to high yields affording the corresponding hydroxyalkyl derivatives. The stereochemistry of the ring-opening reaction follows the rules of a classical S_N2 mechanism. The resulting linear products can be cyclized to furylidene ketones in high yields by treatment with hot acetic acid. Under these conditions even the product arising from reaction of trimethylsilylethylene oxide gives the ring closure instead of the elimination product.