On the Mechanism of Conversion ofN-Acyl-4-acyloxy-β-lactams into 2-Substituted 1,3-Oxazin-6-ones. Can a Low-Barrier Transition State Be Antiaromatic?
Citations Over TimeTop 13% of 2001 papers
Abstract
The mechanism of the conversion of N-acyl-4-acyloxy-beta-lactams into 1,3-oxazin-6-ones has been investigated using ab initio and density functional theories. It has been found that two pseudopericyclic reactions are involved in the whole process. The first key reaction is a retro-[4-exo-dig] cyclization instead of a thermal conrotatory electrocyclic ring opening. Magnetic characterization of the corresponding transition structure shows antiaromatic character, despite the low activation energy associated with this process. The second step is very exothermic and has no activation barrier. It corresponds to another pseudopericyclic reaction instead of a six-electron disrotatory electrocyclization. These results confirm that there is no correlation between aromaticity and pseudopericyclic reactions. In contrast, thermal-symmetry-allowed pericyclic reactions are always aromatic. Therefore, magnetic analysis of the corresponding transition structures constitutes a useful tool to distinguish between both kinds of processes.
Related Papers
- → Aromaticity and Pericyclic Reactions(1971)363 cited
- → On the Mechanism of Conversion ofN-Acyl-4-acyloxy-β-lactams into 2-Substituted 1,3-Oxazin-6-ones. Can a Low-Barrier Transition State Be Antiaromatic?(2001)46 cited
- → ‘Forbidden’ Electrocyclizations of Diradicaloids(2019)7 cited
- → Diastereoselectivity in an electrocyclization reaction of cyclopentadienones(2007)5 cited
- → A Simple and Novel Approach To Delineating Stereochemistry of Electrocyclic Reactions(2012)2 cited