Pipecolic acid-catalyzed direct asymmetric Mannich reactions
Pipecolic acid-catalyzed direct asymmetric Mannich reactions
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DOI：
10.1021/ol052861o
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发表时间：
2006-03-02
期刊：
影响因子：
5.2
通讯作者：
Barbas, CF
中科院分区：
文献类型：
--
作者：
Cheong, PHY;Zhang, HL;Barbas, CF
以(S)-吡喃甲酸为催化剂，研究了N-对甲氧基苯基保护的α-亚氨基乙醛与醛的Mannich反应。这些反应得到了具有高对映体选择性(>；98%ee)的合成物和ANT产物(dR=1.4-2：1)。与之相反，(S)由脯氨酸催化的反应主要是生成具有高对映选择性的合成产物。计算结果表明，与脯氨酸相比，S-顺式-烯胺和S-反式-烯胺的过渡结构之间的能量优势较小，产生的(2S，3R)-ANT和(2S，3S)-SYN Mannich产物的量几乎相等。
Mannich reactions between aldehydes and N-p-methoxyphenyl-protected alpha-imino ethyl glyoxylate have been performed using (S)-pipecolic acid as catalyst. The reactions give both syn- and ant products (dr = 1.4-2:1) with high enantioselectivities (> 98% ee). In contrast, (S)proline-catalyzed reactions give mainly syn-products with high enantioselectivities. Computational studies reveal that the energetic preference between the transition structures involving the s-cis-enamine and the s-trans-enamine is smaller for the pipecolic acid as compared to proline, yielding the (2S,3R)-anti and the (2S,3S)-syn Mannich product in nearly equal amounts.