Deprotonation of p-tert-butyltetramethoxycalix[4]arene with butyllithium gives a nucleophilic intermediate species that reacts with N,N-dimethylformamide (DMF) to install a formyl group at the 2-position. The 2-formylcalixarene can be isolated in ca. 50% recrystallized yield. If the reaction is carried out with adventitious oxygen present, a second compound, a 2-oxo calixarene species, is also formed, likely by an autoxidation–decarbonylation pathway. The reaction can be steered to the 2-oxo product following the reaction with DMF by aerating the reaction mixture and treating it with nBu4NF to facilitate the conversion, resulting in a 57% recrystallized yield of 2-oxo-p-tert-butyltetramethoxycalix[4]arene. This ketone exists in CDCl3 solution predominantly as a ca. 1:1 mixture of two conformers, judged by 1H NMR spectroscopy to be a C1 symmetric partial cone and a C2 1,2-alternate conformation. In both cases the rings flanking the carbonyl group are believed to be anti to one another. The ketone did not react cleanly with Grignard reagents but did react with ethyllithium and butyllithium. In the latter case, the tertiary alcohol so generated was dehydrated to an alkene, which, upon conversion to a tetrahydroxy species, exists in the cone conformation as judged by 1H NMR spectroscopy.

Synthesis and reactions of 2-oxo-p-tert-butyltetramethoxycalix[4]arene

249th National Meeting (2015)

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