Banwell M G, Harvey J E, Hockless D C, Wu A W
School of Chemistry, The University of Melbourne, Parkville, Victoria, Australia.
J Org Chem. 2000 Jul 14;65(14):4241-50. doi: 10.1021/jo991791u.
The readily prepared gem-dibromocyclopropanes (+/-)-13 and (+/-)-19 each engage in a silver(I)-promoted electrocyclic ring-opening/pi-allyl cation cyclization sequence to deliver the hexahydroindole (+/-)-20, which participates in a Suzuki cross-coupling reaction with arylboronic acid 3 to give the tetracyclic compound (+/-)-21. Catalytic hydrogenation of this last compound proceeds in a completely stereoselective manner to give the saturated analogue (+/-)-24, which undergoes Bischler-Napieralski cyclization on reaction with phosphorus oxychloride. The resulting lactam (+/-)-25 is then reduced with lithium aluminum hydride to give (+/-)-gamma-lycorane [(+/-)-1]. By using (-)-menthyl-derived carbamates 27 and 28, this chemistry has been extended to the synthesis of the (+)- and (-)-modifications of the title compound.
易于制备的偕二溴环丙烷（±）-13和（±）-19各自参与银（I）促进的电环化开环/π-烯丙基阳离子环化序列，以得到六氢吲哚（±）-20，其与芳基硼酸3进行铃木交叉偶联反应，得到四环化合物（±）-21。最后一种化合物的催化氢化以完全立体选择性的方式进行，得到饱和类似物（±）-24，其与三氯氧磷反应进行比施勒-纳皮耶拉尔斯基环化。然后用氢化铝锂还原得到的内酰胺（±）-25，得到（±）-γ-石蒜碱[（±）-1]。通过使用（-）-薄荷醇衍生的氨基甲酸酯27和28，这种化学方法已扩展到标题化合物的（+）-和（-）-变体的合成。
