- Iridium-Catalyzed Hydrochlorination and Hydrobromination of Alkynes by Shuttle Catalysis
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Described herein are two different methods for the synthesis of vinyl halides by a shuttle catalysis based iridium-catalyzed transfer hydrohalogenation of unactivated alkynes. The use of 4-chlorobutan-2-one or tert-butyl halide as donors of hydrogen halides allows this transformation in the absence of corrosive reagents, such as hydrogen halides or acid chlorides, thus largely improving the functional-group tolerance and safety profile of these reactions compared to the state-of-the-art. This method has granted access to alkenyl halide compounds containing acid-sensitive groups, such as tertiary alcohols, silyl ethers, and acetals. The synthetic value of those methodologies has been demonstrated by gram-scale synthesis where low catalyst loading was achieved.
- Yu, Peng,Bismuto, Alessandro,Morandi, Bill
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supporting information
p. 2904 - 2910
(2020/01/25)
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- Vinylcations, 39. Zinc Chloride Catalysed Addition of Hydrogen Chloride to Cyclopropylalkynes
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Zinc chloride catalysed addition of hydrogen chloride to 1-cyclopropylalkynes 5a-e (R = CH3, c-C3H5, phenyl, p-tolyl, 4-methoxyphenyl) is studied and the results are compared with those of the addition of HCl/ZnCl2 to several substituted arylalkynes 10a-h.Thus, the alkynes are reacted with HCl/ZnCl2 in dichloromethane and the reaction products are investigated also with respect to their stereochemistry.All alkynes yield predominantly the direkt hydrogen chloride addition products.The 1-cyclopropylalkynes 5a-d give (E)-1-chloro-1-cyclopropyl-1-alkenes 15, and (E)-1-chloro-2-cyclopropyl-1-(4-methoxyphenyl)ethene (16e) is obtained as the major product from 5e (R = 4-CH3OC6H4).Moreover, ring opening to homoallenyl chlorides 19 and, as a side reaction, formation of the ketones 17 and 18 by the addition of water are observed.In a secondary addition reaction, the dichlorides 20 are also obtained by homoallyl rearrangement.The arylalkynes 10a-g react preferentially with formation of (E)-1-aryl-1-chloroalkenes 21.Relative rates are obtained by inter- and intramolecular competition reactions of the alkynes 23 and 5b-e with HCl/ZnCl2 showing the order of stabilization by substituents of the intermediate vinyl cation 2 to be 4-ClC6H4 E2 mechanism.The preferential formation of the addition products E-15, E-16, and E-21 is attributed to a syn-vinyl cation ion pair and to steric approach control of the β-substituents in the vinyl cation intermediate 2.
- Hanack, Michael,Weber, Erhard
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p. 777 - 797
(2007/10/02)
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