Partial OH → Me Replacement in the Calixarene Scaffold: Preparation, Conformation, and Stereodynamics of Tetra-tert-butyl-25,27-dihydroxy-26,28-dimethylcalix[4]arene and Its Dimethyl Ether Derivative

Abstract

The first example of the replacement of hydroxyl groups of a calixarene by methyls is described. Reaction of the bis(spirodienone) calixarene derivative 3B with MeLi afforded the bis addition product 4 which is derived, as shown by X-ray crystallography, from attack on the face of the carbonyls which is anti to the ether oxygen. The reaction of the alternant bis(spirodienone) calixarene derivative 3A with excess MeLi resulted in addition to the CO groups, but with a concomitant cleavage of the spiro bonds. Ionic hydrogenation (CF3COOH/Et3SiH) of this product (5) yielded 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-dimethylcalix[4]arene (6) while ionic hydrogenation of 4 resulted in fragmentation of the macrocyclic ring. Calixarene 6 adopts a 1,3-alternate conformation both in solution and in the solid state. 6 is conformationally flexible, and an inversion barrier of 15.1 kcal mol-1 was measured for it by DNMR. The dimethyl ether derivative of 6 (i.e., 7) exists in a partial cone (paco) conformation ...