Template effects in the formation of a tetramethylene-bridged hemicarceplex

We report a study of the template effect in the formation of tetramethylene-bridged hemicarceplex 7.guest. Two tetrol cavitands were bridged with 1,4-dibromobutane in the presence of suitable template (guest) molecules in N-formylpiperidine as solvent. Selectivity was observed when competing templates were present during the reaction: the relative templating abilities (template ratios) of 30 different guest molecules range by 3600-fold, and manifest a significant preference for para-disubstituted benzenes. Twenty-one of the 30 hemicarceplexes used in this templation study are new. The trend in guest selectivity is markedly different from previous studies in which smaller cavities (e.g., carceplex 2.guest) are formed. In such studies, capsule 3.guest was a good transition state model, whereas this is not the case in the present work.