With a view to develop a general regioselective route to pyridazine analogues of benzofurocoumarins, the angular compound 3 and the linear compound 9 were synthesized. In both cases the key step in the construction of the fused pyridazine ring was a Diels-Alder reaction of the intermediate dihydrofura-3-ones with 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine. The furocoumarinone precursor 2 of compound 3 was synthesized in 60% yield by regioselective Fries rearrangement of 7-(chloroacetyloxy)coumarin (1). The benzofuranone 7, the precursor of compound 9, was obtained in a preparatively useful scale and 34% overall yield from ethyl 2,4-dimethoxycinnamate (4) in 3 steps by regioselective Friedel-Crafts chloroacetylation and further cyclization. The coumarin skeleton of compound 9 was completed in the final step by lactonization with BBr3.
为了开发
苯并呋喃香豆素哒嗪类似物的一般区域选择性路线,我们合成了角状化合物 3 和线状化合物 9。在这两种情况下,构建融合
哒嗪环的关键步骤都是中间体二氢
呋喃-3-酮与 3,6-双(三
氟甲基)-
1,2,4,5-四嗪的 Diels-Alder 反应。化合物 3 的
呋喃香豆酮前体 2 是通过 7-(
氯乙酰氧基)
香豆素(1)的区域选择性弗里斯重排合成的,收率为 60%。化合物 9 的前体
苯并呋喃酮 7 是以
2,4-二甲氧基肉桂酸乙酯(4)为原料,通过区域选择性弗里德尔-卡夫斯
氯乙酰化反应和进一步环化反应,分三步制备得到的,总收率为 34%。化合物 9 的
香豆素骨架在最后一步通过 BBr3 内酯化完成。