The Knoevenagel reaction of unprotected sugars was investigated in the 1950s using zinc chloride as promoter. The so-called Garcia Gonzalez reaction had been almost forgotten for 50 years, until the emergence of new water tolerant catalysts having Lewis acid behavior. The reaction was thus reinvestigated and optimal conditions have been found to prepare trihydroxylated furan derivatives from pentose or beta-tetrahydrofuranylfuran from hexoses with non-cyclic beta-keto ester or beta-diketones. Other valuable compounds such as beta-linked tetrahydrobenzofuranyl glycosides or hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione can be obtained using cyclic beta-dicarbonylic derivatives. Apart from one report in the 1950s, the Knoevenagel reaction of unprotected carbohydrate in basic condition has been studied only in the mid-1980s to prepare C-glycosyl barbiturates from barbituric acids and, later on, from non-cyclic beta-diketones, beta-C-glycosidic ketones. The efficient method exploited to prepare such compounds has found an industrial development in cosmetics.

中文翻译：

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未保护的糖的Knoevenagel反应。

在1950年代，使用氯化锌作为促进剂研究了未保护糖的Knoevenagel反应。所谓的加西亚·冈萨雷斯（Garcia Gonzalez）反应几乎已经被遗忘了50年，直到出现具有路易斯酸行为的新型耐水催化剂。因此，对该反应进行了重新研究，并发现了最佳条件，可从戊糖或含非环状β-酮酯或β-二酮的己糖中制备β-四氢呋喃基呋喃的三羟基化呋喃衍生物。其他有价值的化合物，例如β-连接的四氢苯并呋喃基糖苷或羟烷基-3,3,6,6，-四甲基-3,4,5,6,7,9-六氢-1H-x吨-1,8（2H）-二酮可以使用环状β-二羰基衍生物获得。除了1950年代的一份报告外，仅在1980年代中期才研究了未保护碳水化合物在碱性条件下的Knoevenagel反应，该反应由巴比妥酸和随后的非环状β-二酮，β-C-糖苷酮制备C-糖基巴比妥酸酯。用于制备此类化合物的有效方法已在化妆品中发现了工业发展。