“…(b) Base-Catalyzed 1,3-Hydrogen Shift. Several examples of this type of transformation are described in cycloheptatrienic systems, catalyzed by triethylamine, − 1,8-diazabicyclo[5.4.0]undec-7-ene, , or potassium tert -butoxide. , The mechanism and regioselectivity have been studied for cycloheptatrienes bearing electron-withdrawing groups. − There are also a few examples of thermal, − photochemical, or acid-catalyzed 57,58 1,3-hydrogen shifts. In most cases, the hydrogen atom shifts from a ring-junction position to the nearest unsubstituted position (path A, Scheme ). ,,− ,− In the case where cycloheptatriene 18 has R 1 ≠ H (path B, Scheme ), the 1,3-shift is very unfavored.…”