Rhodium(II)-carbenoid C-H insertion reactions in the synthesis of β-oxospirane systems

A simple one-pot procedure is described for the preparation of spiro[4.4]nonane-2,7-dione derivatives from open chain bis(alpha-diazoketones) by two consecutive intramolecular Rh(II)-catalyzed carbenoid insertion reactions. With 1-diazo-4-(3-oxocycloalkyl)butan-2-ones as substrates, the methodology provides 2,7-dioxospiranes with a cyclopentane ring spiroannulated onto a five-, six- or seven-membered cycloalkane.