Acta Chimica Sinica ›› 2012, Vol. 70 ›› Issue (14): 1518-1522.DOI: 10.6023/A12060346 Previous Articles     Next Articles

Communications

不对称双酸催化3,4-二氢-2H-吡喃的反电子Hetero-Diels-Alder反应

吕健, 钟兴仁, 程津培, 罗三中   

  1. 中国科学院化学研究所 北京分子科学国家实验室 分子识别与功能院重点实验室 北京 100190
  • 投稿日期:2012-06-26 发布日期:2012-07-12
  • 通讯作者: 罗三中
  • 基金资助:

    项目受国家自然科学基金(Nos. 20972163, 21025208)和973项目(No. 2012CB82160)资助.

Asymmetric Binary-Acid Catalysis in the Inverse-Electron-Demanding Hetero-Diels-Alder Reaction of 3,4-Dihydro-2H-Pyran

Lv Jian, Zhong Xingren, Cheng Jin-Pei, Luo Sanzhong   

  1. Beijing National Laboratory for Molecular Sciences BNLMS, CAS Key Laboratory of Molecular Recognition and Functions, Institute of Chemistry, the Chinese Academy of Sciences, Beijing 100190
  • Received:2012-06-26 Published:2012-07-12
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 20972163, 21025208) and 973 program (No. 2012CB82160).

Chiral dihydropyrans are important structural units in a plethora of bio-active natural products. Inverse-electron- demanding hetero-Diels-Alder reaction between α,β-unsaturated enones/enals and olefins represents one of the most straightforward pathway to access chiral dihyropyrans moieties. Though this reaction has been much explored in asymmetric catalysis, new catalytic strategy or catalysts are still desirable in order to further address the limited scopes and applicability. Previously, we have developed asymmetric binary acid catalysis (ABC) as a powerful combinatorial approach for chiral strong acid catalysis. In principle, the ABC strategy utilizes chiral Br?nsted acid, e.g. chiral phosphoric diester acid, as dual ligand and acid, in concert with typical metal Lewis acid, resulting in synergistic catalysis due to their mutually enhanced acidity/electrophilicity as well as the endowed multi-activation sites. To advance the application of ABC strategy in the above mentioned reaction, we have found that the use of metal salt of chiral phosphoric acid instead of free phosphoric acid in the presence of an achiral Lewis acid, led to much improved activity and stereoselectivity, thus providing a conceptual advance to include two Lewis acids combinations in ABC catalysis. The obtained optimal Lewis acids combination, InBr3 and Ca(1c)2, was found to be an effective and selective catalyst for the HDA reaction of 3,4-dihydro-2H-pyrans. In the presence of InBr3 (2.5 mol%) and Ca(1c) (2.5 mol%), the reaction occurred smoothly to afford the desired 3,4-dihydro-2H-pyrans in high yield (85%—98%), with moderate to excellent diastereoselectivity (70:30—99:1, endo/exo) and enantioselectivity (up to 94% ee) under 25℃ in CH2Cl2. Different enol ethers 2 and β,γ-unsaturated α-ketoesters 3 all worked well with excellent diastereoselectivity (94:6) and good enantioselectivity under the optimal reaction conditions.

Key words: asymmetric catalysis, Hetero-Diels-Alder reaction, indium bromide, chiral calcium phosphate, 3,4-dihydro-2H-pyran