Selective O-methylations of 3-[(triphenylphosphoranylidene)acetyl]tetronic and -tetramic acids
作者:Marina Harras、Tobias Bauer、Rhett Kempe、Rainer Schobert
DOI:10.1016/j.tet.2013.03.004
日期:2013.5
3-enoyltetronates and -tetramates as occurring in natural products, the 1′-methoxy isomers 8 and 9 are typically unreactive bisacyl ylides. This was rationalised by an X-ray structural analysis and ab initio calculations. However, the formal Wittig products of 8 and 9 are accessible in two steps via Wittig olefination of ylides 4/5 followed by 1′-O methylation of the resulting alkenes.
Tetronic和四酸与累积的叶立德Ph 3 PCCO反应,得到3-[((三苯基膦亚基)乙酰基]衍生物4和5。这些可以用Meerwein盐选择性地甲基化,我3Ø+高炉4-在杂环的4-O原子处,或在1,8-双(二甲基氨基)萘(质子海绵)存在下,在酰基内酯的O-原子上存在。尽管4-甲氧基烷基化物6和7与醛进行维蒂希反应,得到相应的3-烯酰基四氢酸酯和-四酸酯,如在天然产物中出现的,但是1'-甲氧基异构体8和9通常是不反应的双酰基烷基化物。这是通过X射线结构分析和从头算得到的。然而,正式产品的Wittig 8和9是在通过叶立德Wittig烯化两个步骤访问的4 / 5 然后将所得烯烃进行1'-O甲基化。