Control of stereochemistry in an intramolecular Diels–Alder reaction by the phenylsulfonyl group; an improved synthesis of pisiferol
作者:Edward J. Bush、David W. Jones
DOI:10.1039/a702761c
日期:——
Thermolysis of 4a (XÂ =Â H) gives 6a and 6b (XÂ =Â H) in a ratio of 1â¶4 whereas 4b (XÂ =Â SO2Ph) gives more of the trans-ring junction product 6a (XÂ =Â SO2Ph) suitable for the synthesis of pisiferol [ratio 6aâ¶6b (XÂ =Â SO2Ph)Â =Â 1.5â¶1]. Base catalysed elimination of the phenylsulfonyl group from 6a (XÂ =Â SO2Ph) gives 18 which is hydrogenated to 6a (XÂ =Â H), an intermediate in the synthesis of pisiferol. Both 6a and 6b (XÂ =Â SO2Ph) have ring B in a half-boat conformation.
4a (XÂ =Â H)热分解得到 6a 和 6b (XÂ =Â H),二者的比例为 1¶4,而 4b (XÂ =Â SO2Ph)则得到更多的反式环连接产物 6a (XÂ =Â SO2Ph),适合合成 pisiferol [比例 6a¶6b (XÂ =Â SO2Ph)Â =Â 1.5¶1]。在碱催化下,6a(XÂ =Â SO2Ph)中的苯磺酰基被消除,得到 18,再经氢化得到 6a(XÂ =Â H),它是合成 pisiferol 的中间体。6a 和 6b(XÂ =Â SO2Ph)的环 B 都呈半舟构象。