A GaCl3-catalyzed [4+1] cycloaddition of α,β-unsaturated carbonyl compounds and isocyanides leading to unsaturated γ-lactone derivatives

A GaCl3-catalyzed reaction of α,β-unsaturated ketones with isocyanides leading to the formation of unsaturated lactone derivatives is described. This is the first example of the catalytic [4+1] cycloaddition of ∞,β-unsaturated ketones and isocyanides. GaCl3 is an excellent catalyst due to its lower oxophilicity, which is desirable for all of the key steps, such as E/Z isomerization, cyclization, and deattachment from the products. Copyright © 2003 American Chemical Society.