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.

Asymmetric total synthesis of (+)-virosine A via sequential nucleophilic cyclizations onto an activated formamide.

The first synthesis of tetracyclic alkaloid virosine A is reported. The natural alkaloid was prepared in only 13 steps, in an enantioenriched form. The azabicyclo[2.