A facile regioselective construction of spiro epoxy-bridged tetrahydropyranone frameworks

Investigations on the reactivity profile of the transient five-membered-ring cyclic carbonyl ylides, generated from α-diazo ketones, in the presence of the CO group of various simple ketones and symmetrical/unsymmetrical 1,2-diones were carried out. The reaction of α-diazo ketones with 1,2-naphthoquinone furnished interesting diastereomeric cycloadducts in which both the CO groups acted as dipolarophilic sites. The similar reaction in the presence of several isatin derivatives afforded novel spiro dioxa-bridged indole derivatives as a mixture of diastereomers. The single crystal X-ray structure analysis manifestly revealed the mode of cycloaddition and the stereochemistry of two of the diastereomers. A diverse set of novel spiro epoxy-bridged tetrahydropyranone frameworks have been constructed in good yield via the tandem cyclization–cycloaddition of α-diazo ketones with the CO group as heterodipolarophile in a regioselective manner.