5,8-Dihydronaphthalene-1,4-diol,
readily available from benzoquinone and buta-1,3-diene, is isomerized
by heating with strong sodium hydroxide, and acetylated (Ac2O), in situ, to form 5,8-diacetoxy-1,2-dihydronaphthalene.
Catalysed (AlCl3) addition of acetyl chloride followed by dehydrochlorination (LiCI/HCONMe2) yielded
5,8-diacetoxy-3-acetyl-1,2-dihydronaphthalene (11) in 82% overall yield. Base
hydrolysis of (11), followed by methylation (Me2SO4)
gives 3-acetyl-5,8-dimethoxy-1,2-dihydronaphthalene in 94% yield, the most
direct route to this product so far described. More importantly, the diacetate (11) is selectively deacetylated
at C5 (Cs2CO3 in tetrahydrofuran, or K2CO3
in Me2SO) to form the related phenol, alkylation
of which produces the 5-alkoxy compound. Further hydrolysis followed
by alkylation yields the unsymmetrically,
but regiospecifically substituted, 3-acetyl-5,8-dialkoxy-1,2-dihydronaphthalenes.
This method is specifically illustrated by the production of
3-acetyl-5-benzyloxy-8-methoxy-1,2-dihydronaphthalene which is formed in a
short, cost effective synthesis in a moderate overall yield (25%) based upon
benzoquinone as starting material;significantly, no
chromatographic separations are required.
5,8-二氢萘-1,4-二醇、
5,8-二氢萘-1,4-二醇很容易从苯醌和丁-1,3-二烯中获得。
用强氢氧化钠加热并就地乙酰化(Ac2O),生成 5,8-二乙酰氧基-1,2-二氢萘。
催化(AlCl3)加入乙酰氯,然后脱氢氯化(LiCI/HCONMe2),得到
5,8-二乙酰氧基-3-乙酰基-1,2-二氢萘 (11),总收率为 82%。碱
11)的碱水解,然后进行甲基化(Me2SO4
得到 3-乙酰基-5,8-二甲氧基-1,2-二氢萘,收率为 94%。
到目前为止所描述的获得该产品的最直接途径。更重要的是,二乙酸酯 (11) 可选择性地在 C5
在四氢呋喃中的 Cs2CO3 或在 Me2SO 中的 K2CO3
在 Me2SO 中)脱乙酰基,生成相关的苯酚,再将其烷基化
生成 5-烷氧基化合物。进一步水解
进一步水解,然后进行烷基化反应,生成不对称但有特定区域取代的 5-烷氧基化合物、
3-乙酰基-5,8-二烷氧基-1,2-二氢萘。
这种方法的具体例子是生产
3- 乙酰基-5-苄氧基-8-甲氧基-1,2-二氢萘的生产就是这种方法的具体例证。
3- 乙酰基-5-苄氧基-8-甲氧基-1,2-二氢萘。
以苯醌为起始原料,以中等的总收率(25%)进行简短、经济高效的合成。
无需色谱分离。