The N,O-bridged sesquinorbornadienes: a testing ground for establishing the superiority of N-Z Pyrrole over furan as a dienofuge n retro-diels-alder reactions

<p> <em>N</em>-R pyrroles (R=H, Z, COPh but not Bn, TMS) <strong>6</strong> add selectively at rt to the substituted π-bond of 2,3-bis(trifluoromethyl)-7-oxanorbornadiene <strong>7</strong> under high pressure (14 kbar) to form exclusively the <em>syn</em>-facial <em>N,O-</em>sesquinorbornadienes <strong>8</strong>; at higher temperatures the thermodynamic stereoisomers <strong>10</strong>,<strong>11</strong> are produced by cycloreversion and reaction at the unsubstituted π-bond. The exclusive loss of <em>N</em>-Z pyrrole from the <em>N</em>-Z derivative of <strong>8</strong> demonstrated the superior dienofugacity of <em>N</em>-Z pyrrole over furan; kinetic studies showed that the activation energy for this fragmentation was 34.7 kcal mol−1. This selectivity is in accord with theory (AM1, ab initio). </p>