The first synthesis and characterisation of elusive cone 1,2-diformyl tetralkoxycalix[4]arenes and their derivatives

The synthesis and isolation of elusive tetralkoxycalix[4]arenes 2 in the cone conformation and bearing two formyl groups in proximal (1.2) positions at the upper rim are described for the first time. They were obtained as a mixture with the distal (1,3) regioisomers 3 by optimizing the Gross formylation reaction on the tetralkoxycalix[4]arenes 1. After reduction to the corresponding alcohols, compounds 4 could be isolated and oxidized to 1,2-diformyl (2) and 1,2-diacid (6) tetralkoxycalix[4]arenes. These 1,2-difunctionalized derivatives are useful intermediates for the synthesis of calixarene-based molecular receptors having proximal binding groups.