Restricted rotation involving the tetrahedral carbon-VI. Some Diels-Alder adducts derived from 2-t-butylfuran

1 - t - Butyl - 1,4 - dihydronaphthalene 1,4 - endoxide derivatives were prepared by treating 2 -t- butylfuran with some benzynes to see the effect of the bulkiness on the barrier to rotation. The NMR signals of the t-Bu group of these compounds split at low temperature, showing that the rotation about the C^Bu-C₁ bond was frozen on the NMR time scale. Activation parameters for rotation were obtained by the total line shape analysis. On further lowering of the temperature, the restricted rotation of the Me in t-Bu group was observed. The signals of the Me groups were assigned by taking the chemical shifts and the through-space H-F couplings into consideration.