Functionalized and partially or differentially bridged resorcin[4]arene cavitands: Synthesis and solid-state structures

We report the synthesis and structural characterization of modified Cram-type, resorcin[4]arene-based cavitands. Two main loci on the cavitand backbone were selected for structural modification: the upper part (wall domain) and the lower part (legs). Synthesis of unsymmetrically bridged cavitands with different wall components (i.e., 7, 8, and 14-18) was performed by stepwise bridging of the four couples of neighboring, H-bonded OH-groups of octol 1a (Schemes 1, 2, 4, and 5). Cavitands with modified legs (i.e., 20, 24, 27, and 28), targeted for surface immobilization, were synthesized by short routes starting from suitable aldehyde starting materials incorporating either the fully preformed leg moieties or functional precursors to the final legs (Schemes 7-10). The new cavitand substitution patterns described in this paper should enable the construction of a wide variety of functional architectures in the future. X-Ray crystallography afforded the characterization of cavitands 2c (Fig. 3) and 24 (Fig. 7) in the vase conformation, with 2c featuring a well-ordered CH2Cl2 guest molecule in its cavity. A particular highlight is the X-ray crystal-structure determination of octanitro derivative 19 (Scheme 6), which, for the first time, shows a cavitand, lacking substituents in the ortho-position to the two O-atoms of the four resorcinol moieties, in the kite-conformation (Fig. 5).