A strained bridgehead unsaturated bond between tricoordinate and pentacoordinate boron (opens in new tab)

Bridgehead olefins such as anti-Bredt olefins and bicyclo[2.2.0]hex-1(4)-enes possess a highly strained C=C bond, rendering them exceptionally reactive and prone to distinctive chemical behaviour. Almost all reported examples are transient species that have not yet been validated by X-ray crystallography. Formal isoelectronic replacement of carbon with heteroatoms enables the construction of bonding and structural motifs corresponding to their organic counterparts. However, isolated heteroato...