Stereochemical Control over Three Contiguous Stereogenic Centers in the Intramolecular Ene Reaction of Activated 1,6-Dienes. Application to the Synthesis of (±)-Methyl Cucurbate and (±)-Methyl Epijasmonate
作者:Tarun K. Sarkar、Binay K. Ghorai、Sandip K. Nandy、Bireswar Mukherjee、Asoke Banerji
DOI:10.1021/jo961739n
日期:1997.8.1
The influence of a protected alcohol group adjacent to the ene or enophile component on diastereoselectivity in both thermal and Lewis acid-catalyzed 5-(3,4) ene reactions of a series of 1,6-dienes 1-7 has been studied. The results indicate that its effect can be considerable, and in one example, with a gem-dimethyl group on the connecting chain and a large silyl protecting group on the hydroxyl, the diastereocontrol was almost perfect, with three stereogenic centers and one double bond geometry set up in one step, e.g., 4 --> 10. This new finding was exploited in a synthesis of epijasmonoid natural products, (+/-)-methyl cucurbate (19) and (+/-)-methyl epijasmonate (18) starting from aldehyde 24, where the key step was a highly diastereocontrolled 5-(3,4) ene cyclization 23 --> 22.