Brønsted Acid-Catalyzed Cycloisomerization of But-2-yne-1,4-diols with or without 1,3-Dicarbonyl Compounds to Tri- and Tetrasubstituted Furans

A Brønsted acid-catalyzed method to prepare tri-
and tetrasubstituted furans efficiently from cycloisomerization of
but-2-yne-1,4-diols with or without 1,3-dicarbonyl compounds is described.
By taking advantage of the orthogonal modes of reactivity of the alcoholic
substrate through slight modification of the reaction conditions,
a divergence in product selectivity was observed. At room temperature, p-TsOH·H2O-mediated tandem alkylation/cycloisomerization
of the propargylic 1,4-diol with the β-dicarbonyl compound was
found to selectively occur to provide the tetrasubstituted furan product.
On the other hand, increasing the reaction temperature to 80 °C
was discovered to result in preferential p-TsOH·H2O-catalyzed dehydrative rearrangement of the unsaturated alcohol
and formation of the 2,3,5-trisubstituted furan adduct.

本研究报道了一种以布朗斯特酸（Brønsted acid）为催化剂的合成方法，以丁-2-炔-1,4-二醇（but-2-yne-1,4-diols）为底物（无论是否添加1,3-二羰基化合物（1,3-dicarbonyl compounds）），通过环异构化反应即可高效制备三取代与四取代呋喃类化合物。通过对反应条件进行细微调控，借助醇类底物的正交反应活性模式，可实现产物选择性的定向分化。研究表明，在室温条件下，对甲苯磺酸一水合物（p-TsOH·H₂O）介导的炔丙基1,4-二醇与β-二羰基化合物（β-dicarbonyl compound）的串联烷基化/环异构化反应，可选择性生成四取代呋喃产物。与之相对，当将反应温度升高至80℃时，该体系会优先发生对甲苯磺酸一水合物催化的不饱和醇脱水重排反应，进而得到2,3,5-三取代呋喃加合物。