Unusual Rearrangement of a 1,8-Naphthalene Derivative

The steric strain between nitro and carboxylic acid groups in an 8-nitro-1-naphthoic acid derivative is able to unexpectedly disrupt the aromaticity of the naphthalene core under mild reaction conditions. The addition of H₂O to the aromatic ring of a highly strained naphtho oxazinium intermediate induces the fragmentation of a Csp²-Csp² bond, with a concomitant rearrangement to yield a conjugated aldehyde. Key intermediates have been characterized, and the X-ray structure of the derivative has been obtained. Density functional theory (DFT) studies were performed to confirm the proposed mechanism.