本題目為利用有機催化反應，合成四取代1,3,4,5-吡唑化合物。在此反應中，以20 mol% DL-脯胺酸為催化劑，進行巴豆醛及苯腙之 [3+2]-環加成反應，芳香化後得到產物吡唑，產率30-51%。DL-脯胺酸首先活化巴豆醛，生成亞胺離子中間體，與苯腙進行 [3+2]-環化反應，芳香化後，便得到四取代吡唑化合物。

An organocatalytic synthesis of 1,3,4,5-tetrasubstituted pyrazole was described. In this study, 20 mol% DL-proline catalyzed the [3+2] cycloaddition of crotonaldehyde with phenylhydrazone followed by aromatization, leading to the pyrazole formation in moderate yield (30-51%). DL-proline activated crotonaldehyde by in situ generation of imium ion intermediate, so that the [3+2] cyclization with phenylhydrazone and aromatization could proceed.

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