Synthesis of the Kopsia alkaloids (±)-pauciflorine B, (±)-lahadinine B, (±)-kopsidasine, (±)-kopsidasine-N-oxide, (±)-kopsijasminilam and (±)-11-methoxykopsilongine
作者:Philip Magnus、Lewis Gazzard、Lindsay Hobson、Andrew H. Payne、Trevor J. Rainey、Neil Westlund、Vince Lynch
DOI:10.1016/s0040-4020(02)00243-0
日期:2002.4
treated with AgBF4/THF followed by aqueous NaHCO3 it was converted into (±)-kopsidasine 2, completely characterized as its derived N-oxide 2a. Treatment of 26 with AgBF4/THF followed by aqueous NaHCO3, gave 31. Oxidation of 31 with m-chloroperoxybenzoic acid resulted in the N-oxide 32 which underwent fragmentation to give 33 when exposed to trifluoroacetic anhydride. When the diene 33 was treated with Mn(dpm)3
Pictet-Spengler将13与色胺进行缩合反应得到14,然后转化为17。用氯甲酸苯酯处理17产生18,进行环环化生成19。通过用Tf 2 O / DMAP处理18以生成18f,并用三甲基甲硅烷基氰化物淬灭反应来制备更稳定的氰基类似物22。在75°C下用丙烯酰氯(过量)处理22,得到23,将其直接用N-羟基-2-硫代吡啶酮/ Et 3 N处理,得到24。在t- BuSH存在下照射24导致还原性脱羧,得到26和少量的2-硫代吡啶基醚25。要保护26中的苯胺氮,需要先使用三光气/吡啶,然后再使用甲醇。将27转化为28的最后一步需要共轭还原α,β-不饱和酯,然后进行α-羟基化,得到28(11,12-脱甲氧基拉哈丁宁B)。干净地将26暴露于PhI(OAc)2 / MeOH中,得到26a,然后用Zn / AcOH将其直接还原为29。如前所述,将29转化为30,当用AgBF 4 / THF然后用NaHCO