Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Thermolysis of dimethyl 2‐[(3‐oxo‐3<jats:italic>H</jats:italic>‐isoindol‐1‐yl)oxy]malonate (<jats:bold>8</jats:bold>) promotes a [1,4]‐H shift in the imidic NCOCH fragment of the starting molecule, which leads to a reactive carbonyl ylide. This carbonyl ylide can be trapped by the CN bond of imidates and imines, as well as the CO bond of benzaldehyde. The corresponding cycloadducts <jats:bold>11, 14</jats:bold>, and <jats:bold>16</jats:bold> are formed regioselectively in good yields (60–95%) and with high stereoselectivity. In the case of <jats:bold>11</jats:bold>, the minor cycloadduct in solution undergoes an isomerization to give the more stable stereoisomer. The structures of two cycloadducts, <jats:italic>i.e.</jats:italic>, <jats:bold>11a</jats:bold> and <jats:bold>14a</jats:bold>, have been established by X‐ray crystallography.</jats:p>