Asymmetric Diels-Alder reactions catalyzed by a triflic acid activated chiral oxazaborolidine
Asymmetric Diels-Alder reactions catalyzed by a triflic acid activated chiral oxazaborolidine
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DOI：
10.1021/ja025848x
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发表时间：
2002-04-17
影响因子：
15
通讯作者：
Lee, TW
中科院分区：
文献类型：
--
作者：
Corey, EJ;Shibata, T;Lee, TW
本文报道了一种用三氟甲磺酸质子化非刘易斯酸性恶唑硼烷（1）制备手性刘易斯超强酸的新方法。得到的阳离子物种（3）是各种1，3-二烯与α，β-烯醛的Diels−桤木反应的强有力和高对映选择性催化剂。优化研究（见表1）导致选择非常有效的反应条件和催化剂（6A和6 B）。该反应操作简单，重复性好，经济性好，因为只有Ca。需要6mol%的催化剂。此外，手性催化剂前体易于回收再利用（>95%效率），并且可商购获得。表2中列出的14个示例记录了该过程的广泛范围。根据最近为这类涉及二烯对络合物7的面进攻的催化对映选择性反应制定的机理原理，成功地预测了6A和6 B催化的Diels−桤木反应的绝对立体化学过程。产生刘易斯超强酸6A和6 B的方式允许将催化能力刘易斯和质子酸联系起来的近似比较（或比例）。
This paper reports a new method for the generation of chiral Lewis superacids by protonation of a non-Lewis acidic oxazaborolidine (1) with triflic acid. The resulting cationic species (3) are powerful and highly enantioselective catalysts for the Diels−Alder reaction of various 1,3-dienes with α,β-enals. An optimization study (see Table 1) led to the selection of reaction conditions and catalysts (6Aand6B) which are very effective. The reactions are simple to conduct, reproducible, and economical, since only ca. 6 mol % of catalyst is required. In addition, the chiral catalyst precursor is readily recovered for reuse (>95% efficiency) and is commercially available. The broad scope of the process is documented by the 14 examples listed in Table 2. The absolute stereochemical course of the Diels−Alder reactions catalyzed by6Aand6Bwas successfully predicted on the basis of the mechanistic principles which have recently been formulated for this type of catalytic enantioselective reaction involvingre-face attack by the diene on complex7. The mode of generation of Lewis superacids6Aand6Ballows an approximate comparison (or scale) connecting the catalytic power Lewis and protic acids.