Oximes and oxime ethers have found multiple uses, including as drugs and pesticides. Oxidation of these types of compounds leads to the formation of reactive intermediates whose reactivity is not well understood. Previous work in our lab has proposed that under these conditions, oximes react to form iminoxyl radicals, whereas oxime ethers form oxime ether radical cations. A recent study has shown that upon oxidation, oxime ethers with built in aromatic rings can form phenanthridines in good yields and with high regioselectivity through intramolecular cyclization. The present work is an extension of the previous work with the focus on a series of o-arylalkynyl oximes to see whether the alkyne group acts as a radical trap or a nucleophile. The oximes and oxime ether substrates were exposed to UV light in the presence of a photosensitizer for up to 8 hours and the reactions were followed by nuclear magnetic resonance (NMR). Under these conditions, oximes were found to react, whereas oxime ethers did not. Irradiation of o-alkynylaryl oximes in the presence of 9,10-dicyanoanthracene (DCA) was found to result in the formation of a proposed 5-exo dig cyclization product, tentatively identified as (E)-1-benzylidene-3-methyl-1H-isoindole 2-oxide (scheme 1). Isolation of the product has been complicated by that fact that the product is unstable, however, computational (ab initio) data is consistent with formation of (E)-1-benzylidene-3-methyl-1H-isoindole 2-oxide under these conditions. Current work is focused on the characterization of the major photolysis product, as well as isolation and identification of the secondary product.

Photooxidation of o-alkynylaryl oximes: Intramolecular cyclization reaction

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.