I have a penchant for nucleophilic displacement reactions at heteroatoms. I suppose Prof. Narasaka is to blame for this obsession. I got my first taste of Sn2 pocesses at sp2-hybridized nitrogen about 15 years ago and it left a lasting impression as something that is not readily expected based on conventional wisdom. Tonight’s post is related to this class of processes. It gets even better, though, because the end result of the reaction below is a highly fluorescent molecule. The lead author of the Chem. Eur. J. paper – Prof. Saczewski of Gdansk, Poland – might not have been interested in obscure Sn2 reactions at nitrogen, but the documented development of a series of neat fluorescent dyes (subbed Safiriniums) shown below, is sure to make Prof. Narasaka happy. The route to a representative Safirinium molecule depicted below involves a sequence wherein a Mannich reaction initially results in the formation of a tertiary amine, which attacks the nitrogen center of the nearby benzoisoxazolone. Someone should look at the energetics of this reaction, paying special attention to rate dependence on the angle of attack. It is probably fun to study kinetics of this process using fluorescence spectroscopy. Oh, and one more thing: the goal of the study reported by Saczewski was to create fluorescent sensors for formaldehyde, upon which the Mannich process hinges. You never know what you’re going to get out of literature these days.

http://onlinelibrary.wiley.com/doi/10.1002/chem.201302085/abstract