Study of the rearrangement of cyclononatetraenyl(dipropyl)borane to 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene by NMR spectroscopy

Using NMR spectroscopy it was found that at ambient temperature 9-cyclononatetraenyl(dipropyl)borane (1) rapidly rearranges to give 7,8-dipropyl-7-borabicyclo4.2.2]deca-2,4,9-triene (2),cis-endo-9-dipropylborylbicyclo6.1.0]nona-2,4,6-triene (3a), and two isomeric boranes with dihydroindene skeletons (4a,b) (the ratio2 :3a :4a,b is 10 : 1 : 2).cis-exo-9-Dipropylborylbicyclo6.1.01nona-2,4,6-triene (3b) is an intermediate product of the rearrangement; it is formed as a result of 8-electrocyclization inE,Z,Z,Z-cyclononatetraenyl(dipropyl)boranela. The transformation of bicycle3b 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 thea-C atom). Borane6 formed in this rearrangement rapidly isomerizes to2 via a 1,3]-B shift.For preliminary report see Ref. 1Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 117–124, January, 1996.