Preparation, Stereochemistry, and Reactions of the Bis(spirodienone) Derivatives of p-tert-Butylcalix[4]arene

The stereochemistry of the spirodienone derivatives of p-tert-butylcalix[4]arene (1) is analyzed. Treatment of 1 with base and 2 equiv of phenyltrimethylammonium tribromide resulted in the formation of a mixture of three main products (4A, 4A′, and 4B) each containing two spirodienone moieties. The molecules slowly mutually interconvert in solution, and in toluene at 80 °C the equilibrium mixture is composed of 10% 4A′, 65% 4A, and 25% 4B. From the NMR data, it is concluded that both 4A and 4A′ are systems in which the two cyclohexadienone groups are at distal positions (1,3) whereas 4B has C₈ symmetry and the cyclohexadienone rings are at proximal (1,2) positions. Unambiguous structural characterization of the systems was achieved by X-ray crystallography which indicates that 4A′ is the chiral form (C₂ symmetry) while 4A is the meso (C_i) form. Attempted reduction of 4A resulted in the regeneration of 1. Reaction of 4A with HCl results in chloro-de-tert-butylation of two rings and rearomatization. Reaction of 4A, 4A′, and 4B with excess benzyne yielded the corresponding Diels-Alder adducts 10A, 10A′, and 10B which do not interconvert in solution. Based on the NMR data it is concluded that for each compound the additions to the two spirodienones occurred with identical diastereofacial discrimination. The Diels-Alder adducts are the first systems in which the phenolic oxygens of a calixarene were converted into nonconjugated ketone groups.