Efficient Asymmetric Carbonyl-Ene Reactions Catalyzed by Platinum Metal Lewis Acid Complexes of Conformationally Flexible NUPHOS Diphosphines: A Comparison with BINAP

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• 作者：Simon Doherty ; Julian G. Knight ; Catherine H. Smyth ; Ross W. Harrington ; William Clegg
• 刊名：Organometallics
• 出版年：2007
• 出版时间：December 3, 2007
• 年：2007
• 卷：26
• 期：25
• 页码：6453 - 6461
• 全文大小：192K
• 年卷期：v.26,no.25(December 3, 2007)
• ISSN：1520-6041

文摘

A comparative study of the Lewis acid-catalyzed carbonyl-ene reaction of a range of monosubstituted,unsymmetrical 1,1-disubstituted and trisubstituted alkenes with ethyl trifluoropyruvate revealed thatplatinum complexes of enantiopure conformationally flexible tropos NUPHOS diphosphines rival oroutperform their atropisomeric enantiopure BINAP counterpart. The stereochemical integrity of theseNUPHOS diphosphines remains intact over extended periods, as evidenced by the high ee's obtained foran unreactive substrate requiring >20 h to reach good conversions and the presence of a singlediastereoisomer after addition of (S,S)-DPEN to the reaction mixture. The absolute and relativestereochemistry of a number of the ene products has been determined by single-crystal X-raycrystallography. The sense of asymmetric induction, the regioselectivity, and the exo diastereoselectivityare consistent with a stereochemical model based on a square-planar catalyst·pyruvate adduct. Theallylbenzene derivatives required for this study were conveniently prepared by the palladium-catalyzedcross-coupling between the corresponding aromatic bromide and allylmagnesium bromide using a catalystmixture based on Pd₂(dba)₃ and a NUPHOS diphosphine.