Aluminum‐Catalyzed Hydroalkoxylation at Elevated Temperatures: Fast and Simple Access to Coumarans and Other Oxygen Heterocycles
Aluminum‐Catalyzed Hydroalkoxylation at Elevated Temperatures: Fast and Simple Access to Coumarans and Other Oxygen Heterocycles
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DOI：
10.1002/cctc.201300182
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发表时间：
2013-11
期刊：
影响因子：
4.5
通讯作者：
J. Schlüter;Max Blazejak;Lukas Hintermann
中科院分区：
文献类型：
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作者：
J. Schlüter;Max Blazejak;Lukas Hintermann
铝催化的非活化烯烃的分子内氢烷氧基化是制备氧杂环化合物的有力合成工具，这对于制备生物和药物活性化合物具有重要意义。异丙醇铝催化（5摩尔%）的2-烯丙基苯酚在高温（250 ° C，20分钟）下的环化以异常快速、简单和经济的方式提供2-甲基香豆素（2-甲基-2，3-二氢苯并呋喃）。此外，将烯丙基芳基醚与异丙醇铝（5摩尔%）加热，通过串联Claisen重排-氢烷氧基化反应得到2-甲基香豆素。对于任一反应，催化剂耐受具有各种官能团的宽范围的底物。通过使用弱亲电的烷氧基铝作为催化剂，在本反应条件下可以排除"隐藏的布朗斯台德酸"催化的发生。
An aluminum‐catalyzed intramolecular hydroalkoxylation of nonactivated alkenes is presented as a powerful synthetic tool for the preparation of oxygen heterocycles, which are of major interest for the preparation of biological and pharmaceutical active compounds. The aluminum isopropoxide catalyzed (5 mol %) cyclization of 2‐allylphenols at elevated temperatures (250 °C, 20 min) provides 2‐methylcoumarans (2‐methyl‐2,3‐dihydrobenzofuran) in an exceptionally fast, simple, and economic manner. Moreover, heating of allyl aryl ethers with aluminum isopropoxide (5 mol %) gives 2‐methylcoumarans by a tandem Claisen rearrangement–hydroalkoxylation reaction. For either reaction, the catalyst tolerates a broad scope of substrates with various functional groups. By using the weakly electrophilic aluminum alkoxide as the catalyst, occurrence of “hidden Brønsted acid” catalysis can be excluded under the present reaction conditions.