Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

• Holger F. Bettinger and
• Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

• aromatics; Dewar isomer; reaction mechanism; Introduction The barrier for ring opening of Dewar benzene (1) to yield benzene (2) is high enough to give this benzene valence isomer a half life of about two days [1] at room temperature despite the significant exothermicity (60–70 kcal mol−1) of the

• -azaborine (4), a boron-nitrogen heterocycle that is isoelectronic and isosteric with benzene [15], results in its Dewar isomer 2-aza-3-borabicyclo[2.2.0]hex-5-ene (3) under the conditions of cryogenic noble gas matrix isolation [16]. Under these experimental conditions (T < 35 K), the isomerisation back to