conformational studies by dynamic NMR. 62. Stereomutations of rotamers and of conformational enantiomers in 1,2-diacylbenzenes

摘要

A number of 1,2-diacylbenzenes have been investigated by dynamic NMR spectroscopy. The 1,2- formyl derivative 1 was found to exist (at-162 deg C) in the nearly coplanar ZE AND EE conformations (70/100 and 30/100, respectivity) that interconvert with a free energy of activation of 4.9 kcal mol~1. On the contrary, the more hindered 1,2-diisobutanolylbenzene (4) adopts a twisted conformation (as indicated by the ~13C spectrum at-157 deg C) which, in principle, might correspond either to a meso or to a racemic stereolabile structure.