Cavitands with introverted functionality stabilize tetrahedral intermediates

The synthesis and characterization of two deepened cavitand hosts with introverted functionality--functional groups directed into the cavity--is described. Two functions can be introverted, alcohol and aldehyde, and they show the formation of hemiacetals and hemiketals on binding small guests with complementary functional groups. The structures of the bound hemiacetals are determined by 1D and 2D NMR studies. The arrangements of the guests in the cavitands enhance the equilibrium constants of carbonyl additions, K/K(ctrl), between 13- and 10(5)-fold, compared to their counterparts in solution. The stabilization of the addition products is due to the prior complexation of the guests and the organized solvation provided to the tetrahedral intermediates by a network of secondary amides at the cavitand rim.