Payne rearrangement

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NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition phase

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t-BuS- is a bulky nucleophile, so direct attack on the secondary epoxide is slow. Under basic conditions the neighbouring alkoxide group attacks intramolecularly to make a new, rearranged epoxy alcohol. The new reactive primary electrophilic site undergoes an SN2 reaction with the t-BuS- under the conditions of the rearrangement. Notice how the blue OH, which started on carbon 1, has ended up on carbon 2.

G. B. Payne, J. Org. Chem., 1962, 27, 3819–3822.