Abstract: In this article we describe a new methodology for the total synthesis of 3,4-unsubstituted coumarins from commercially available starting materials. Six examples were prepared, including five naturally occurring coumarins—7-hydroxy-6,8-dimethoxy-coumarin (isofraxidin), 7-hydroxy-6-methoxycoumarin (scopoletin), 6,7,8-trimethoxy-coumarin, 6,7-dimethoxycoumarin (scoparone), and 7,8-dihydroxycoumarin (daphnetin) and one synthetic coumarin, 7-hydroxy-6-ethoxycoumarin. Moreover, five important o-hydroxybenzaldehyde intermediates were also obtained, namely 2,4-dihydroxy-3,5-dimethoxybenzaldehyde, 2,4-dihydroxy-5-methoxybenzaldehyde, 5-ethoxy-2,4-dihydroxy-benzaldehyde, 2-hydroxy-3,4,5-trimethoxybenzaldehyde, and 2-hydroxy-4,5-dimethoxy-benzaldehyde. The method developed herein involves just three or four steps and allows for the rapid synthesis of these important molecules in excellent yields. This is the first synthesis of 6,7,8-trimethoxycoumarin and 7-hydroxy-6-ethoxycoumarin.
Keywords: 3,4-unsubstituted coumarins; o-hydroxybenzaldehyde derivatives; 6,7,8-trimethoxycoumarin; 7-hydroxy-6-ethoxycoumarin
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Gao, W.; Li, Q.; Chen, J.; Wang, Z.; Hua, C. Total Synthesis of Six 3,4-Unsubstituted Coumarins. Molecules 2013, 18, 15613-15623.
Gao W, Li Q, Chen J, Wang Z, Hua C. Total Synthesis of Six 3,4-Unsubstituted Coumarins. Molecules. 2013; 18(12):15613-15623.
Gao, Wenqing; Li, Qingyong; Chen, Jian; Wang, Zhichao; Hua, Changlong. 2013. "Total Synthesis of Six 3,4-Unsubstituted Coumarins." Molecules 18, no. 12: 15613-15623.