Reactions of the diazadiboretidines I [R = Me, Et, Bu, CMe3 (II)] with Lewis acids, protic reagents, and multiple bond systems are described. 1:1 Adducts are formed from I [R = Et III)] and the Lewis acids ZnCl2 and AlCl3. III is protolyzed by Me3COH and Me3CNH2 in a 1:1 reaction giving the open-chain products IV (R1 = Et; X = Me3CO, Me3CNH). The enolization products IV [R1 = Bu, X = CH2:CR2O (R2 = Me, Ph, CMe3)] are isolated from the reaction of I with the ketones MeCOR2. In the presence of ZnCl2, ring opening of I (R = Me, Et) is obsd. with 1-alkynes, HC.tplbond.CR3 (R3 = H, CMe3, Ph, CO2Me), yielding the products IV (same R; X = C.tplbond.CR3). The same alkynes are added to the sterically crowded II without opening of the ring to give V. A ring expansion of I (R = Bu) to give the six-membered rings occurs on reaction with the CO groups of R4CHO [R4 = Me, CMe3, CMe:CH2, Ph], (CF3)2CO, and partly MeCOPh. Six-membered ring VI may be synthesized by the addn. of Ph2C:C:O to III. Six-membered rings VII (R = Me, Et) were obtained from I (R = Me, Et) and MeO2CC.tplbond.CCO2Me, whereas II and the same alkyne gave the 1:2 bicyclic adduct VIII. The central structural unit of VII (R = Me) is a nonplanar, twisted six-membered ring from an x-ray structure anal. The bicyclo[2.2.0]hexene homologs IX are formed from I (R = Et, CMe3) and EtO2CN:NCO2Et.