There continues to be significant interest in convenient methodologies for the efficient synthesis of heteroaromatic ring systems. A number of studies have shown that o-alkynyloxime derivatives can undergo efficient electrophilic cyclization, yielding isoquinoline or isoquinoline N-oxide derivatives. However, not much attention has been focused on the oxime radical cation or iminoxyl radical cyclization processes of o-alkynyloxime derivatives. Our previous studies have shown that oxime derivatives can form reactive radical species under photooxidation, which suggests that cyclization might be possible in the case of o-alkynyloximes. In order to study this possibility as well as the regioselectivity of these cyclization processes, we prepared a series of o-alkynylbenzaldehyde and acetophenone oximes and oxime ethers.The oximes were subjected to photooxidation or thermal oxidation in different solvents and the product formation was followed by GC/MS and NMR. The results obtained so far suggest that a 6-exo-dig cyclization is one of the possible pathways, although the process is not selective and the products from the reaction are unstable. This presentation will discuss the influence of substituents, solvent, oxidizer and other factors on the cyclization pathways and other reactions of the reactive intermediates derived from the o-alkynyloximes. The outcomes are compared to known electrophilic cyclization methods of similar substrates.

Oxidative cyclization pathways of o-alkynyloxime derivatives

248th National Meeting (2014)

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