On the mechanism of conversion of N-Acyl-4-acyloxy-β-lactams into 2-substituted 1,3-oxazin-6-ones. Can a low-barrier transition state be antiaromatic?

1. Alajarín, M.
2. Sánchez-Andrada, P.
3. Cossío, F.P.
4. Arrieta, A.
5. Lecea, B.