A Computational Investigation of the Selective Cleavage of Diastereotopic Cyclopropane Bonds in 5-spirocyclopropane Isoxazolidines Rearrangement
2019
The complete path of the Brandi-Guarna rearrangement of 5-spirocyclopropane isoxazolidines has been investigated by means of density functional theory calculations to rationalize the competing formation of tetrahydropyridones and enaminones by the determination of the minimum energy reaction paths. Our calculations confirm that the rearrangement is triggered by the homolysis of isoxazolidine N-O bond followed by cleavage of one of the two C-CH$_2$ cyclopropane bonds as previously proposed by Fabian group [Eur. J. Org. Chem. 2001 (2001) 4223]. In addition, the results of this work suggest that, in the presence of a stereogenic center at isoxazolidine C-4', the formation of a piperidinone or an enaminone as final product depends on which of the two diastereotopic C-CH$_{2}$ bonds of cyclopropane is cleaved in the second step of the process. The result can be of great interest for the understanding of other processes involving the opening of a cyclopropane ring.
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