| Abstract
| - Condensation reaction of o-phthalaldehyde with primary amines is a classical method for thesynthesis of phthalimidines. Although the intermediacy of the corresponding monoimines has beenoccasionally proposed, the mechanism of their transformation into phthalimidines remains to beelucidated. We present here theoretical evidence supporting a three-step mechanistic pathway forthat transformation involving the [1,5]-H sigmatropic rearrangement of the aldehydic proton leadingto an intermediate (aminovinyl)ketene as the key step. Other alternative routes have been calculatedto be energetically less favorable. Similar transformations of related imino aldehydes enclosing a5-aza-2,4-pentadienal skeleton via [1,5]-H shifts are also studied.
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