作者:Hidemitsu Uno、Katsuji Sakamoto、Erina Honda、Kaori Fukuhara、Noboru Ono、Junya Tanaka、Masahiro Sakanaka
DOI:10.1039/b007859j
日期:——
Regioselective halogenation of 3-acetoxymethyl-7-chloro-5,8-dimethoxy-1-naphthol 5 was achieved by DBH or I2/N-methylmorpholine to give the corresponding 2-halogeno-1-naphthols 8 and 11, which were converted to 1-methoxymethoxy-3-(alk-2-ynoyloxymethyl)-2-halogenonaphthalenes 17 and 18 in good yields. An intramolecular acyl-transfer reaction of the 2-halogenonaphthalenes triggered by halogen–lithium exchange with BuLi at −78 °C gave 1-methoxymethoxy-2-alkynoyl-3-(hydroxymethyl)naphthalenes 21 in high yields. After protection of the hydroxymethyl group as a benzoate, formation of a γ-pyrone ring was easily achieved by deprotection of the methoxymethyl group followed by spontaneous 6-endo ring closure under mildly acidic conditions. The pyrone derivative having a 1-methylpropyl group was successfully converted to espicufolin 1.
通过DBH或I2/N-甲基吗啉实现3-乙酰氧基甲基-7-氯-5,8-二甲氧基-1-萘酚5的区域选择性卤化,得到相应的2-卤代-1-萘酚8和11,将其转化为1-甲氧基甲氧基-3-(烷-2-炔酰氧基甲基)-2-卤代萘17和18的产率良好。在-78 °C 下,通过与 BuLi 进行卤素-锂交换引发的 2-卤代萘的分子内酰基转移反应以高产率生成 1-甲氧基甲氧基-2-炔酰基-3-(羟甲基)萘 21。将羟甲基保护为苯甲酸酯后,通过甲氧基甲基的脱保护,然后在弱酸性条件下自发的 6-内环闭合,很容易形成 γ-吡喃酮环。具有1-甲基丙基的吡喃酮衍生物被成功转化为espicufolin 1。