PARTIAL OH-]ME REPLACEMENT IN THE CALIXARENE SCAFFOLD - PREPARATION, CONFORMATION, AND STEREODYNAMICS OF -BUTYL-25,27-DIHYDROXY-26,28-DIMETHYLCALIX[4]ARENE AND ITS DIMETHYL ETHER DERIVATIVE

The first example of the replacement of hydroxyl groups of a calixaren e by methyls is described. Reaction of the bis(spirodienone) calixaren e derivative 3B with MeLi afforded the bis addition product 4 which is derived, as shown by X-ray crystallography, from attack on the face o f 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 C=O groups, but with a concomitant cleava ge of the spiro bonds. Ionic hydrogenation (CF3COOH/Et3SiH) of this pr oduct (5) yielded t-butyl-25,27-dihydroxy-26,28-dimethycalix[4]arene ( 6) while ionic hydrogenation of 4 resulted in fragmentation of the mac rocyclic ring. Calixarene 6 adopts a 1,3-alternate conformation both i n 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 con e (pace) conformation and undergoes two distinct dynamic processes pos sessing barriers of 13.3 and 18.1 kcalmol(-1). Molecular mechanics cal culations predict correctly the preferred conformation of 6 and 7 and indicate that the topomerization pathways resulting in the mutual exch ange of the protons within a methylene group are the following: 1,3-al t --> paco(CH3) --> 1,2-alt --> paco(CH3) --> 1,3-alt* for 6, and pac o(CH3) --> 1,3-alt --> paco(OCH3) --> 1,2 alt --> paco(OCH3) --> 1,3- alt --> paco(CH3)* for 7 with calculated barriers of 15.0 and 16.1 kc al mol-l, respectively.