Efficient synthesis and host-guest properties of a new class of calix[6]azacryptands

[GRAPHICS] Two members of a new class of calix[6]azacryptands, namely, calix[6]tampo and calix[6]tamb, have been synthesized through an efficient [1+1] macrocyclization reactionreduction sequence. One of them has been obtained in a remarkably high overall yield from the known X6H3Me3. In comparison to all the other calix[6] azacryptands, they possess unique conformational properties since they present a rigidified cone conformation with a partial filling of the cavity by the methoxy groups. In contrast to calix[6] tampo, the fully protonated derivative of calix[6] tamb behaves as a remarkable molecular receptor toward polar neutral guests. NMR studies have shown that the intracavity binding process is governed by a conformational flip of the aromatic walls of the calixarene core.