A series of 3-diazoalkanediones, when treated with a catalytic quantity of a rhodium (II) carboxylate, were found to afford oxabicyclic dipolar cycloadducts derived by the trapping of a carbonyl ylide intermediate. The reaction involves generation of the 1, 3-dipole by intramolecular cyclization of the keto carbenoid onto the oxygen atom of the neighboring keto group. Both five-and six-ring carbonyl ylides are formed with the same efficiency. A ...
