The Inheritance Angle: A Determinant for the Number of Members in the Substituted Cucurbit[n]uril Family

Two new glycoluril diethers have been prepared, bearing strained cyclobutene and cyclobutane rings at the fused junction of the two imidazolidinone rings. The wide angle of the concave face of the cyclobutano derivative enabled the synthesis of cyclobutanocucurbit[5–8]uril, the largest member being the most significant achievement. A limited binding affinity study compared the new substituted family to classical cucurbit[5–8]uril. Surprisingly lower affinities were found, except for cyclobutanocucurbit[6]uril, which was 3.3-fold higher.