Assignment of E–Z-configurations of spiro-oxirane-oxindoles synthesized by rhodium(II) acetate-catalyzed reaction of ethyl diazoacetate with N-methylisatin

ABSTRACT

The rhodium(II) acetate [Rh₂(OAc₄)]-catalyzed reaction of ethyl diazoacetate with N-methylisatin leads to the formation of diastereomeric oxiranes spiro-fused to N-methyl-2-oxindole together with 1,3-dioxolane bis-spiro-fused to N-methyl-2-oxindole. The formation of ylide from the reaction of rhodium-carbenoid with C-3 carbonyl group of the N-methylisatin undergoing a 1,3-cyclization, and a [3 + 2]-dipolar cycloaddition with another molecule of N-methylisatin, respectively, explains the formation of products. The application of nuclear overhauser effect spectroscopy to determine the E–Z-configurations of the spiro-oxirane-oxindoles is demonstrated.

KEYWORDS:

• 1,3-dioxolane
• α-diazocarbonyls
• isatin
• NOESY
• spiro-oxirane

Acknowledgments

We are grateful to the Chemistry Department, University of Botswana, for providing the necessary research facilities.