Zur Kenntnis der thermischen Umlagerung des Bicyclo[1.1.0]butan‐Systems. Eine kinetische Studie des Übergangs von Tricyclo[4.1.0.0 2,7 ]heptanen in Bicyclo[3.2.0]hept‐6‐ene

On the Thermal Rearrangement of the Bicyclo[1.1.0]butane System. A Kinetic Investigation of the Conversion of Tricyclo[4.1.0.0 2,7 ]heptanes into Bicyclo[3.2.0]hept‐6‐enes Tricyclo[4.1.0.0 2,7 ]heptane ( 7 ), its 1‐ ( 20 ) and 2‐phenyl derivatives ( 22 ), tetracyclo[5.1.0.0 2,4 .0 3,5 ]octane ( 17 ), 1,2,3,4‐tetrahydro‐1,2,3‐methenonaphthalene ( 25 ) as well as its 1‐ ( 35 ), 2‐ ( 32 ), and 3‐phenyl derivatives ( 27 ) have been thermolyzed in solution in the temperature range between 110 and 230° C. The activation parameters of these reactions have been determined. The parent hydrocarbon 7 is converted into bicyclo[3.2.0]hept‐6‐ene ( 11 ) in high yield, and the other substrates behave analogously, i.e. the cyclobutene derivatives 18, 21, 23, 26, 28, 33, 34 , and 36 are formed. Arising from 27 , the cyclobutene 28 is observed as intermediate, which is transformed rapidly to a mixture of the benzocycloheptenes 29 and 31 . To undergo this ring enlargement, the other cyclobutenes require more severe conditions. The thermal rearrangements of 20, 22 , and 27 are accompanied by parallel reactions, which have been identified as acid‐catalized processes in the case of 22 and 27 giving rise to the norcarene derivatives 24 and 30 , respectively. In 2‐phenylmethenonanpthalene 32 two pathways to a cyclobutene derivative exist; they are found to be followed in a 82:18 ratio. The relative reaction rates of all substrates investigated can be interpreted in terms of a consistent mechanistic model. Accordingly, the tricyclo[4.1.0.0 2,7 ]heptane system is transformed in a concerted but highly asynchronous process to an ( E,Z )‐1,3‐cycloheptadiene, which then undergoes a rapid conrotatory ring closure to yield the corresponding bicyclo[3.2.0]hept‐6‐ene.