- Enantioselective Olefin Hydrocyanation without Cyanide
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The enantioselective hydrocyanation of olefins represents a conceptually straightforward approach to prepare enantiomerically enriched nitriles. These, in turn, comprise or are intermediates in the synthesis of many pharmaceuticals and their synthetic derivatives. Herein, we report a cyanide-free dual Pd/CuH-catalyzed protocol for the asymmetric Markovnikov hydrocyanation of vinyl arenes and the anti-Markovnikov hydrocyanation of terminal olefins in which oxazoles function as nitrile equivalents. After an initial hydroarylation process, the oxazole substructure was deconstructed using a [4 + 2]/retro-[4 + 2] sequence to afford the enantioenriched nitrile product under mild reaction conditions.
- Schuppe, Alexander W.,Borrajo-Calleja, Gustavo M.,Buchwald, Stephen L.
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supporting information
p. 18668 - 18672
(2019/11/28)
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- Solar photo-thermochemical syntheses of 4-bromo-2,5-substituted oxazoles from N-arylethylamides
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Solar photo-thermochemical C(sp3)-H bromination, conducted efficiently in a specially designed reactor, was reported recently. In the present study, the more complex formation of 4-bromo-2,5-substituted oxazoles from N-arylethylamides using this approach was achieved. The one-pot syntheses were carried out with N-bromosuccinimide-dichloroethane over 6 h (10.00 am to 4.00 pm) on sunny days. The isolated yields were in the range 42-82%. Benzylic bromination, followed by O-C bond formation through intramolecular nucleophilic substitution, and a second benzylic bromination followed by HBr elimination, gave the oxazole ring. A third bromination of the ring yielded the final product. The feasibility of synthesizing thiazole derivatives using a similar approach was also demonstrated. During the course of the reactions, succinimide and HBr were co-generated in the aqueous phase. Treatment with NaBrO3 and additional acid returned the reagent in 57% isolated yield upon chilling. The overall methodology was greener as a result.
- Dinda, Milan,Samanta, Supravat,Eringathodi, Suresh,Ghosh, Pushpito K.
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p. 12252 - 12256
(2014/03/21)
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- Polyarylated thiazoles via a combined halogen dance - Cross-coupling strategy
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The application of the halogen dance reaction for the synthesis of starting materials for cross-coupling reactions is reported. The obtained compounds were then successfully applied, in sequential Stille and Suzuki-Miyaura cross-coupling reactions to obta
- Schnuerch, Michael,Khan, Ather Farooq,Mihovilovic, Marko D.,Stanetty, Peter
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experimental part
p. 3228 - 3236
(2009/12/09)
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- Ethyl 2-chlorooxazole-4-carboxylate: A versatile intermediate for the synthesis of substituted oxazoles
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(formula presented) R1 = Ar, Het, alkenyl R2 = H, Ar, Het, alkenyl, alkynyl R3 = H, CO2H, Ar, Het, alkenyl, alkynyl By using a sequence of regiocontrolled halogenation and palladium-catalyzed coupling reactions,
- Hodgetts, Kevin J.,Kershaw, Mark T.
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p. 2905 - 2907
(2007/10/03)
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- Substituted Oxazoles: Synthesis via Lithio Intermediates
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Reactions of 2-α-, 2-, 4-, and 5-lithiooxazoles are used to prepare various substituted derivatives.Previously unrecognized time dependence for the reaction of a 2-lithiooxazole with benzaldhyde is described, and a rationale for this behavior is offered.Competitive reactions occur when the readily available 2,5-diphenyloxazole is treated with n-butyllithium.Deprotonation of the ortho position of the 2-phenyl group and addition of n-butyl to the 2-position of the oxazole compete with the desired 4-lithiation.The use of sec-butyllithium/catalytic lithium tetramethylpiperidide allows preferential formation of 4-lithio-2,5-diphenyloxazole.This intermediate has been converted to the 4-bromo, -methyl, -hydroxybenzyl, -benzoyl, and -trialkylsilyl derivatives.Lithiation of 2,4-diphenyloxazole and subsequent trimethylsilylation occur readily at the 5-position.Deprotonation of 2-alkyloxazoles occurs at the α-carbon in preference to ring sites.Further reaction of an α-phenyl-2-oxazolemethanol methoxymethyl ether with base and acetyl chloride leads to an acyloin derivative.Chromic acid oxidation is used to prepare both 2- and 4-benzoyloxazoles.The formation of an 2-ethoxyoxazole from 2-oxazolone vis Meerwein salt chemistry is described.
- Whitney, Scott E.,Rickborn, Bruce
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p. 3058 - 3063
(2007/10/02)
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