Design and reactions of a carbon Lewis base/boron Lewis acid frustrated Lewis pair

The conjugated dienamine 4 selectively adds Piers' borane [HB(C 6 F 5 ) 2 ] to give the enamine/borane system 5 , which features a boratirane structure by internal enamine carbon Lewis base to boron Lewis acid interaction. Compound 5 behaves as a C/B frustrated Lewis pair and undergoes typical addition reactions to benzaldehyde, several nitriles and to sulfur dioxide. This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.