Cyanophthalide annulation with 4-(5-alkoxy-2-furyl)-3-buten-2-one. Application to the synthesis of a (naphtho)pyrano-.GAMMA.-lactone.
作者:KEIICHI NOMURA、KOUSUKE OKAZAKI、KOHZO HORI、EIICHI YOSHII
DOI:10.1248/cpb.34.3175
日期:——
Reaction of lithiated 3-cyano-1(3H)-isobenzofuranone (7) with 5-substituted 2-furfuralacetones 6a-c and subsequent O-methylation of the resulting naphthohydroquinones afforded 2-acetyl-3-furylnaphthalenes 8a-c in good yields. Annulation of the dialkoxyphthalides 12a, b with 6a could also be carried out to give 13a, b. The 5-tert-butoxy-2-furyl compounds were stereoselectively transformed into (1R*, 3R*, 4R*)-pyrano-γ-lactones 16a, 18a, b in high yields by a modification of the Kraus method (LiAlH4 reduction followed by treatment of the product carbinol with p-toluenesulfonic acid (TsOH) in acetonitrile and then with 1, 8-diazabicyclo[5.4.0]undec-7-ene in toluene at low temperatures). The 5-methoxy-2-furyl compound 9b also afforded 16a stereoselectively in one step (treatment with TsOH), but this compound was less effective as a substrate of the pyrano-γ-lactone annulation since a side reaction leading to the spiro-γ-lactone 17 became significant. The 5-phenylthio compound 9c failed to give 16a under a variety of conditions.
将石炭酸化的 3-氰基-1(3H)-异苯并呋喃酮(7)与 5-取代的 2-糠醛丙酮 6a-c 反应,然后将生成的萘氢醌进行 O-甲基化,可得到 2-乙酰基-3-呋喃萘 8a-c,产率很高。二烷氧基酞化物 12a 和 b 还可以与 6a 进行环化反应,得到 13a 和 b。通过改良克劳斯法(先用 LiAlH4 还原,然后用对甲苯磺酸 (TsOH) 在乙腈中处理生成的乙醇,再用 1,8-二氮杂双环[5.4.0]十一碳-7-烯在甲苯中低温处理),5-叔丁氧基-2-呋喃化合物被立体选择性地转化为 (1R*,3R*,4R*)-吡喃-γ-内酯 16a,18a,b,产率很高。5-甲氧基-2-呋喃基化合物 9b 也能在一个步骤中立体选择性地得到 16a(用 TsOH 处理),但该化合物作为吡喃-γ-内酯环化反应的底物效果较差,因为产生螺-γ-内酯 17 的副反应变得非常明显。在各种条件下,5-苯硫基化合物 9c 未能生成 16a。