Carcerands and hemicarcerands, in which two calix [4]resorcinarene cavitands are held together by four covalent linkages, have been developed by Cram and others. They have attracted considerable attention from the viewpoint of stabilization of reactive intermediates and as microvesicles for drug delivery by the confinement of guest molecules inside the capsules away from bulk phases. [1] Error correction through thermodynamic equilibration, minimization of synthetic effort by use of modular subunits, and control of assembly processes through subunit design are characteristics of supramolecular approaches to self-assembly. On the basis of this concept, cavitand-based capsules have been constructed under thermodynamic control using noncovalent interactions such as hydrogen bonds, [2] metal coordination, [3] ionic interactions, [4] and solvophobic interactions. [5] As an alternative strategy, dynamic covalent chemistry offers great advantages in supramolecular syntheses because dynamic covalent bonds contain reversible covalent bond-forming and -breaking processes under thermodynamic control. [6] The reversibility of the imine bond-forming reaction has been applied to cavitand-based capsule synthesis. [7] Boronic ester formation is another reliable synthon for dynamic covalent chemistry. [8] Herein, we report the self-assembly of tetrakis-(dihydroxyboryl) cavitand 1 (as a bowl-shaped aromatic cavity) and 1,2-bis(3,4-dihydroxyphenyl)ethane 2 into capsule 3 by dynamic boronic ester formation (Scheme 1). [9] Capsule 3 encapsulates one molecule of guest such as 4,4'-disubstitutedbiphenyl or 2,6-disubstituted-anthracene derivatives in a highly selective recognition event. We also present the on/ off control of capsule formation with guest encapsulation by removal/addition of methanol.
Taken in isolation, the cavitand tetraboronic acid 1 [2d, 10] and the bis(catechol)-linker 2 [11] both have low solubilities in CDCl 3 . However, a 2:4 heterogeneous mixture of 1 and 2 in CDCl 3 gave a homogeneous solution upon heating at 50 8C for 3 h and quantitatively produced capsule 3, wherein two [