Discussion of "Efficient, microwave-assisted intramolecular 1,3-dipolar cycloadditions of oximes and N-methylnitrones derived from o-alkenylmethoxyacetophenones"

Abstract

Heaney and Doyle 1014 The following discussion note arises in defence of comments and assertions made upon our work (1) in the paper entitled “Efficient, microwave-assisted intramolecular 1,3dipolar cycloadditions of oximes and N-methylnitrones derived from o-alkenylmethoxy-acetophenones”, published in the Canadian Journal of Chemistry (2). Ishar and co-workers (2) include in their publication a number of inaccuracies and contradictions of our previously published work (1), the details of which are outlined in the following paragraphs. Firstly, the inaccuracies. The abstract of the paper begins “Contrary to literature reports oximes (2a, 2b) are transformed to nitrones, which undergo regioand stereoselective intramolecular 1,3-dipolar cycloadditions, both on microwave heating under solvent free conditions and refluxing in toluene, to afford novel cycloadducts (5a, 5b); the oxazepine N-oxide (3a) reported to be formed in 98% yield was obtained only as a minor product ( 10%).” The final sentence of the introductory paragraph continues in the same vane, stating “Recently, it has been reported that the oximation of o-allyloxy-acetophenone and -benzophenone (1) affords E-oximes (2), which are quantitatively converted to dipoles (3, Scheme 1) on refluxing in xylene for 14 h (5).” The implication being that our cited work (1) included results on the behaviour of oximes 2, i.e, 2a–2c. This is in error, our publication concerned only the reaction of oxime 2a, it did not include any data on 2b or 2c. Secondly, the contradictions. The reaction of 2a described in the publication by Ishar and co-workers (2) involves heating in toluene at 110 °C for 72 h, whilst our cited work (1) refers to thermal reaction of 2a following 14 h heating in refluxing xylene (140 °C). Within the Results and discussion section of this paper (2), the authors contradict our work (1) no less than four times. The changes in experimental conditions, in terms of both reaction temperature (30 °C lower) and reaction duration (58 h longer) between that reported by Ishar and co-workers (2) and our cited work (1) are of sufficient magnitude to make it completely unreasonable for Ishar and co-workers to conclude that the result of their reaction contradicts our cited result. Indeed, following the publication of the paper by Ishar and co-workers, a researcher in our laboratory, not previously involved with the initial reactions of 2a, repeated our reported work (1); thus, we can confirm that 2a transforms (xylene, 140 °C, 14 h) smoothly to 3a in excellent yield as we previously described (1). The publication of the paper by Ishar and co-workers has publicly and inaccurately discredited our work on the important topic of the relationship between oxime geometry and reactivity. Moreover, this paper has already been cited by respected researchers in our field (3) and we welcome the opportunity to clarify our position with regard to the reaction of oxime 2a.