I came across the following reaction, whose mechanism is said to involve a 1,2-alkyl migration with a double inversion in configuration. The reagents used were nitrous acid (generated in situ) followed by acidic hydrolysis.

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I got a hint that the first step involves the reaction of nitrous acid with the NH group. But, I cannot understand how the reaction works. Could anyone explain the mechanism?

  • 2
    $\begingroup$ Are these structures correct? As drawn the product has gained a methyl group at the top which has no apparent source. $\endgroup$
    – Waylander
    Sep 28, 2023 at 19:59
  • $\begingroup$ There was a mistake in the structure I drew. Thank you for pointing out. $\endgroup$ Sep 29, 2023 at 6:37

1 Answer 1


The OP's original structure is missing a quaternary methyl group (since amended) because the structure 1 is derived from α-santonin[1] with hydroxylamine. Nitrosation of 1 affords 2 that undergoes acid-catalyzed fragmentation to give secondary carbocation 3. A suprafacial 1,2-methyl shift produces tertiary cation 4. Two fates of carbocation 4 may be considered. One is to form intermediate 7 that loses nitrous oxide to give epoxide 6. Alternatively, carbocation 4 loses nitrous oxide forming alcohol 5, which undergoes ring closure to form epoxide 6. These mechanistic considerations are not discussed in the reference.

  1. J. T. Edwards and M. J. Davis, J. Org. Chem., 1978, 43, 536. https://doi.org/10.1021/jo00398a002

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