Rhodium‐Mediated Stoichiometric Synthesis of Mono‐, Bi‐, and Bis‐1,2‐Azaborinines: 1‐Rhoda‐3,2‐azaboroles as Reactive Precursors

A series of highly substituted 1,2‐azaborinines, including a phenylene‐bridged bis‐1,2‐azaborinine, was synthesized from the reaction of 1,2‐azaborete rhodium complexes with variously substituted alkynes. 1‐Rhoda‐3,2‐azaborole complexes, which are accessible by phosphine addition to the corresponding 1,2‐azaborete complexes, were also found to be suitable precursors for the synthesis of 1,2‐azaborinines and readily reacted with alkynyl‐substituted 1,2‐azaborinines to generate new regioisomers of bi‐1,2‐azaborinines, which feature directly connected aromatic rings. Their molecular structures, which can be viewed as boron‐nitrogen isosteres of biphenyls, show nearly perpendicular 1,2‐azaborinine rings. The new method using rhodacycles instead of 1,2‐azaborete complexes as precursors is shown to be more effective, allowing the synthesis of a wider range of 1,2‐azaborinines.