摘要:
In order to investigate the mechanism of the five-membered ring enlargement in carbocation intermediates in steroid biosynthesis, the rearrangement processes in a model carbocation, the 2-cyclopentyl- 2-propyl cation 5, were followed by means of H-1 and C-13 NMR spectroscopy. Carbocations 5A and 5B were prepared in SbF5-SO2,ClF-SO2F2 from the corresponding alcohol precursors. At about - 100 degreesC a ring enlargement process takes place to give the 1,2-dimethylcyclohexyl cation 7. Quantum chemical calculations of model carbocation structures 5A, 5B, 6 and 7 were carried out at the HF/6-3 IG(d) and B3LYP/6-31G(d) levels of theory. Copyright (C) 2000 John Wiley & Sons, Ltd.