Synthesis And Studies On The Conformation Of α,α,α'-trisubstituted Cyclododecanone

On the basis of the study on a-monosubstituted cyclododecanones, , - and a,a'-bissubstiuted cyclododecanones, a series of a, a, a '-trisubstituted cyclododecanones were synthesized by direct bromination of the a-monosubstituted cyclododecanones , , - and , '-bissubstiuted cyclododecanones. The compounds were characterized by IR, 1H NMR, 13C NMR as well as elemental analysis. The conformation of the ring skeletons of these trisubstituted cyclododecanones and possible influencing factors on the conformation of the ring skeletons were discussed in this paper.Results of the x-ray crystal diffraction and NMR data indicated that: Of the three substituents, one substituent presents at a - corner - syn position, the second one is a - corner - anti position and the third one adopt a-side-exo position. The preferred conformations of the ring skeletons of most compounds are [3333]-2-one. However, the preferred conformation of a,cc'-dibrom-a-Benzoylcyclododecanone is [3324]-2-one.According to the data of 'H NMR, a method that based on the Dshift can be used to conclude whether the ring skeleton conformation of the a, a, a'- trisubstituted cyclododecanones would maintain the [3333]-2-one or not. We conclude that when the value of Dshift > 0.45, the conformation of the ring skeleton would change while the conformation would still be the [3333]-2-one if Qshift < 0.45.The conformation of [ortho-1, 10-decylidene]- Pyrazinne was also analyzed by NMR and x-ray crystal diffraction. The results showed that the conformation of cyclododecanyl is [12333], and the planar of the 6-membered ring is perpendicular to that of the two 12- membered rings.