Formal Intramolecular (4 + 1)-Cycloaddition of Dialkoxycarbenes: Control of the Stereoselectivity and a Mechanistic Portrait

The stereoselective synthesis of 5–5, 6–5,
and 7–5 fused O-heterocyclic compounds is
reported. The key reaction is a formal intramolecular (4 + 1)-cycloaddition
involving a dialkoxycarbene and an electron-deficient diene where
the stereoselectivity is dependent on the length of the tether. An
analysis of the stereochemical outcome of this reaction sheds light
on its complex mechanistic picture. High-level calculations were used
to support the proposed mechanistic portrait.