title: Enantio- and Diastereoselective Formal Hetero-Diels-Alder Reactions of Trifluoromethylated Enones Catalyzed by Chiral Primary Amines.
abstract: Enantioselective formal hetero-Diels-Alder reactions of trifluoromethylated enones and 2-amino-1,3-butadienes generated in situ from aliphatic acyclic enones and chiral primary amines are reported. The corresponding tetrahydropyran-4-ones are formed in up to 94 % yield and with up to 94 % ee. The reaction was carried out through a stepwise mechanism, including initial aminocatalytic aldol condensation of 2-amino-1,3-butadiene to the trifluoromethylated carbonyl group followed by an intramolecular oxa-Michael addition. Both NMR investigation and theoretical calculations on the transition state indicate that the protonated tertiary amine could effectively activate the carbonyl group of the trifluoromethyl ketone to promote the addition process through hydrogen-bonding interaction of N-H⋅⋅⋅F and N-H⋅⋅⋅O simultaneously, and thus provide a chiral environment for the approach of amino-1,3-butadienes to the activated trifluoromethyl ketone, resulting in high enantioselectivity.
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China).
authors.forename: Yong-Jun
authors.initials: YJ
authors.lastname: Lin
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China).
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Du
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China).
authors.forename: Tai-Ran
authors.initials: TR
authors.lastname: Kang
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China). quanzhongliu@cwnu.edu.cn.
authors.forename: Quan-Zhong
authors.initials: QZ
authors.lastname: Liu
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China). chenzeqin@cwnu.edu.cn.
authors.forename: Ze-Qin
authors.initials: ZQ
authors.lastname: Chen
authors.affiliation: Chemical Synthesis and Pollution Control, Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, No 1, Shida Road, Nanchong 637002 (P. R. China). longhe@cwnu.edu.cn.
authors.forename: Long
authors.initials: L
authors.lastname: He
keywords: enantioselectivity; enones; hydrogen bonds; organocatalysis; oxygen heterocycles