VASES AND KITES AS CAVITANDS

The syntheses, characterizations, and substituent effects on the vase vs kite conformations of 1-17 are described. These compounds are assembled by two-step syntheses from resorcinol (or 2-substituted derivatives) and aldehydes to form octols 18-26 in high yields, followed by 4-fold bridging reactions with quinoxalines 27-29 or pyrazine 30. In the crystal structure of 3.2CH2Cl2, one CH2Cl2 is enclosed in the vase cavity, while a second CH2Cl2 iS found surrounded by the four (CH2)4Cl groups. When the 2-position of resorcinol is hydrogen, only the vase form of the cavitands exists at 25-degrees-C or higher when quinoxaline bridged, as in 1-7, and at all available temperatures when pyrazine bridged, as in 13. The R and B groups of 1-7 can be varied to control solubility and cavity size without greatly affecting the vase-kite structures. When the 2-position of resorcinol is occupied by a methyl, an ethyl, or a bromine, as in 14-17, only the kite conformation is observed at all available temperatures. When the 2-position is hydrogen and the system is quinoxaline, only the kite conformer is observed at temperatures below -50-degrees-C. When the 2-position is CH3, the kite conformer equilibrates with its dimer. When the 2-position is CH3CH2, as in 17, the kite conformer does not form a dimer. The kite C2v structures under pseudorotation and also dimerize when they contain 2-methylresorcinyl groups to give dimers of D2d symmetry. In some systems, these processes could be differentiated by use of variable-temperature H-1 NMR spectra.