2,7‐Di‐tert‐butyl‐1‐phenyl‐1H‐phosphepine—The First Stable, Monocyclic Phosphepine

Reductive cyclization of the dialdehyde 1 by McMurry reaction is the key step in the synthesis of the title compound 2. According to the 1H-NMR spectrum, 2 is present in the boat conformation. The tert-butyl groups in the positions 2 and 7 hinder isomerization to the structural analogue of norcaradiene and hence also the ready thermal decomposition. R′ = Ph, R = tBu.