The strength of the transannular N→B interaction in the substituted cycloboronate 1,3,5-trioxa-6,8-diaza-2,4-diboracyclooctane1can be controlled both by varying the Lewis basicity of the ring nitrogen atoms and by modifying the steric factors dependent on the nature of the nitrogen substituents (by changing R). Examples of the structural types displaying varying degrees of transannular bonding have been prepared and characterized by X-ray analysis. A simple six-membered cycloboronate structure4containing one boron atom is formed when the basicity of the aminal nitrogen atom is reduced and the boronic acid residue is sterically hindered [R = C(CH3)2CN and Ar = 2,4,6-(CH3)3C6H2]. The bicyclo[3.3.0]octane structure3is obtained when R = simple alkyl and Ar = phenyl. A structural type between1and2is realized when R = C(CH3)2CN and Ar = Ph.