5-Hydroxy-3-methylnaphtho[2,3-c]furan-4,9-dione (1), a metabolite isolated from Aloe ferox and Bulbine capitata, has been synthesized by a sequence involving an annulation reaction between the anion of 4-methoxy-3-oxo-1,3-dihydroisobenzofuran-1-carbonitrile (8) and (E)-pent-3-en-2-one, followed by subsequent construction of the furan ring through allylic bromination, hydrolysis, and dehydration as the key steps. The formation of several unusual products observed in annulation reactions between (8) and O-protected derivatives of (E)-5-hydroxypent-3-en-2-one (9) can be rationalized by invoking the intermediacy of a reactive o-quinone methide. 5,8-Dihydroxy-1-methylnaphtho[2,3-c]furan-4,9-dione (2), another naturally occurring naphtho[2,3-c]furan-4,9-dione, has been prepared by a Friedel–Crafts acylation of 1,4-dimethoxybenzene with 2-methylfuran-3,4-dicarbonyl dichloride. Arguments are presented that 5,8-dihydroxynaphtho[2,3-c]furan-4,9-dione is a better structural representation than the alternative 4,9-dihydroxynaphtho[2,3-c]furan-5,8-dione tautomer in such systems, as the latter would contain a reactive isobenzofuran moiety.
5- 羟基-3-甲基萘并[2,3-c]呋喃-4,9-二酮(1)是从 Aloe ferox 和 Bulbine capitata 中分离出来的一种代谢物,其合成过程包括 4-甲氧基-3-氧代-1、3-二氢异苯并呋喃-1-甲腈 (8) 与 (E)-pent-3-en-2-one 之间的环化反应,然后通过烯丙基溴化、水解和脱水等关键步骤构建呋喃环。在(8)和(E)-5-羟基戊-3-烯-2-酮的 O 保护衍生物(9)之间的环化反应中观察到的几种不寻常产物的形成,可以通过引证反应性邻醌甲酰胺的中间产物而得到合理解释。5,8-二羟基-1-甲基萘并[2,3-c]呋喃-4,9-二酮(2)是另一种天然存在的萘并[2,3-c]呋喃-4,9-二酮,是通过 1,4 二甲基苯与 2-甲基呋喃-3,4-二羰基二氯化物的弗里德尔-卡夫酰化反应制备的。有观点认为,在这种体系中,5,8-二羟基萘并[2,3-c]呋喃-4,9-二酮比 4,9-二羟基萘并[2,3-c]呋喃-5,8-二酮同系物的结构更好,因为后者含有活性异苯并呋喃分子。