Using NMR spectroscopy it was found that at ambient temperature 9-cyclononatetraenyl(dipropyl)borane (1) rapidly rearranges to give 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene (2), cis-endo-9-dipropylborylbicyclo[6.1.0]nona-2,4,6-triene (3a), and two isomeric boranes with dihydroindene skeletons (4a,b) (the ratio 2 : 3a : 4a,b is 10 : 1 : 2). cis-exo-9-Dipropylborylbicyclo[6.1.0]nona-2,4,6-triene (3b) is an intermediate product of the rearrangement; it is formed as a result of 8π-electrocyclization in E,Z,Z,Z-cyclononatetraenyl(dipropyl)borane 1a. The transformation of bicycle 3b to final product 2 occurs apparently via a synchronous exchange of the groups at the B atom (the transformation of the cyclopropane ring to the boracyclobutane ring accompanied by simultaneous migration of the propyl group from the B atom to the α-C atom). Borane 6 formed in this rearrangement rapidly isomerizes to 2 via a [1,3]-B shift.
- 9-cyclononatetraenyl(dipropyl)borane, 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene, 9-dipropylborylbicyclo[6.1.0]nona-2,4,6-trienes
- Electrocyclic reactions, [1,3]-B shift
- NMR spectroscopy
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