Formic Acid as Carbon Monoxide Source in the Palladium-Catalyzed N-Heterocyclization of o-Nitrostyrenes to Indoles

被引:13
作者
Fouad, Manar Ahmed [1 ,2 ]
Ferretti, Francesco [1 ]
Ragaini, Fabio [1 ]
机构
[1] Univ Milan, Dipartimento Chim, I-20133 Milan, Italy
[2] Alexandria Univ, Fac Sci, Chem Dept, Alexandria 21321, Egypt
关键词
REDUCTIVE CYCLIZATION; NITRO-COMPOUNDS; UNFUNCTIONALIZED NITROARENES; INTERMOLECULAR CYCLIZATION; TRIETHYL PHOSPHITE; ARYL BROMIDES; CO; DEOXYGENATION; CARBONYLATION; CONVENIENT;
D O I
10.1021/acs.joc.2c02613
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The reductive cyclization reaction of o-nitrostyrenes to generate indoles has been investigated for three decades using CO as a cheap reducing agent, but it remains an interesting area of research and improvements. However, using toxic CO gas has several drawbacks. As a result, it is highly preferable to use safe and efficient surrogates for in situ generation of CO from nontoxic and affordable sources. Among several CO sources that have been previously explored for the generation of gaseous CO, here we report the use of cheap and readily available formic acid as an effective reductant for the reductive cyclization of o-nitrostyrenes. The reaction is air and water tolerant and provides the desired indoles in yields up to 99%, at a low catalyst loading (0.5 mol %) and without generating toxic or difficult to separate byproducts. A cheap glass thick-walled "pressure tube" can be used instead of less available autoclaves, even on a 2 g scale, thus widening the applicability of our protocol.
引用
收藏
页码:5108 / 5117
页数:10
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