Unprecedented anomalous stereochemistry of halogen additions to syn- and anti-9,9′-bibenzonorbornenylidenes

Exclusive syn(cis)-addition of Br2 to syn-9,9′-bibenzonorbornenylidene (1) took place to give the corresponding vic-dibromide (3) quantitatively with retention of the configuration of 1. Meanwhile, anti(trans)-addition of Br2 to anti-9,9′-bibenzonorbornenylidene (2) also occurred furnishing the same dibromide 3 quantitatively with inversion of the configuration of 2.