The formylation of the upper-rims of thiacalixarenes: synthesis of the first tetra-formylated and the first meta-substituted thiacalix[4]arenes

The conventional Gross reaction for the formylation of the tetrapropoxythiacalix[4]arene using TiCl4 affords the 18-(chloromethyl)-28-hydroxy-25,26,27-tripropoxythiacalix[4]arene substituted in the meta-position of the macrocycle. The p-tetraformyl-tetrapropoxythiacalix[4]arene, which is an interesting intermediate to the upper-rims functionalization of thiacalixarenes, was prepared with a very good yield using BuLi and N-formylpiperidine.