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A mild preparation of substituted indolizines and indole from simple aromatic precursors using (trimethylsilyl)diazomethane In light of the mild conditions and operational simplicity of our indolizine synthesis, we sought to extend the described protocol to the preparation of other heterocycles. Having noted both the presence and proximity of nucleophilic and electrophilic moieties in the 2-(pyridin-2-yl)-acetyl derivatives discussed above, we hypothesized that similarly disposed bifunctional molecules might also prove amenable substrates for heterocycle formation. We were, thus, pleased to discover that 2-aminobenzaldehyde , a bifunctional substrate, could be converted to indole in moderate yield. While the rate of indole formation was slower than that typically observed for the indolizine derivatives described in this Letter, efficient conversion was achieved at 60¡æ using 4 equiv of (trimethylsilyl)diazomethane and 2 equiv of Cs2CO3as an alkaline additive.The utility of this method for the synthesis of functionalized indoles is currently under investigation and will be reported in due course. In conclusion, we have developed a mild and convenient method for the synthesis of substituted indolizines from readily available 2-(pyridin-2-yl)acetyl derivatives using (trimethylsilyl)diazomethane in moderate to good yields (41¨C84%). We have further demonstrated that this reaction can be applied to the synthesis of indole from 2-amino-benzaldehyde and are currently evaluating the feasibility of this synthetic construct for the preparation of substituted indoles and other heterocycles. |
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RXMCDM: ÆÁ±ÎÄÚÈÝ 2014-04-25 15:36:00
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