The insertion of CO into the B−B bond of 1,2‐bis(diisopropylamino)‐2,5‐dihydro‐1H‐1,2‐diborole (1b) and 1,2‐bis(diisopropylamino)‐3‐methylidene‐1,2‐diborolane (1c) leads to the dimeric spiro products 1,7,9,14‐tetrakis(diisopropylamino)‐6,13‐dioxa‐1,7,9,14‐tetraboradispiro[4.2.4.2]tetradeca‐2,10‐diene (4b) and 1,7,9,14‐tetrakis(diisopropylamino)bismethylidene‐6,13‐dioxa‐1,7,9,14‐tetraboradispiro[4.2.4.2]tetradecane (4c). Insertions of CO into the B−B bonds of the cyclic organo‐1,2‐diborane compounds 5, 6, and 7 are not observed. The reaction of 1b with tert‐butyl isocyanide and 2,6‐dimethylphenyl isocyanide in THF leads to the formation of the monomeric insertion products 1,3‐bis(diisopropylamino)‐2‐tert‐butylimino‐1,3‐diboracyclohex‐4‐ene (10b) and 1,3‐bis‐(diisopropylamino)‐2‐(2′,6′‐dimethylphenylimino)‐1,3‐diboracyclohex‐4‐ene (11b). The treatment of 1cwith the isonitriles yields 2‐tert‐butylimino‐1,3‐bis(diisopropylamino)‐4‐methylidene‐1,3‐diboracyclohexane (10c) and 1,3‐bis(diisopropylamino)‐2‐(2′,6′‐dimethylphenylimino)‐4‐methylidene‐1,3‐diboracyclohexane (11c). The steric requirements of the isonitrile insertion products 10b, c and 11b, c prevent their dimerisation and rearrangement. 11b rearranges to 1‐(diisopropylamino)‐2‐(diisopropylaminohydroxyboryl)‐2‐(2′,6′‐dimethylphenylamino)‐1‐boracyclopent‐3‐ene (12b) upon reaction with water from sodium sulfate decahydrate. The compositions of the compounds are derived from the 1H‐, 11B‐, 13C‐NMR data as well as from mass‐spectral and C, H, N analyses. In the cases of of 4b and 12b they have been proven by X‐ray structure analyses.