30273-57-5Relevant academic research and scientific papers
Enolate-Based Regioselective Anti-Beckmann C-C Bond Cleavage of Ketones
Jahn, Ullrich,Ma?ek, Tomá?
, p. 11608 - 11632 (2021/09/02)
The Baeyer-Villiger or Beckmann rearrangements are established methods for the cleavage of ketone derivatives under acidic conditions, proceeding for unsymmetrical precursors selectively at the more substituted site. However, the fragmentation regioselectivity cannot be switched and fragmentation at the less-substituted terminus is so far not possible. We report here that the reaction of ketone enolates with commercial alkyl nitrites provides a direct and regioselective way of fragmenting ketones into esters and oximes or ω-hydroxyimino esters, respectively. A comprehensive study of the scope of this reaction with respect to ketone classes and alkyl nitrites is presented. Control over the site of cleavage is gained through regioselective enolate formation by various bases. Oxidation of kinetic enolates of unsymmetrical ketones leads to the otherwise unavailable "anti-Beckmann"cleavage at the less-substituted side chain, while cleavage of thermodynamic enolates of the same ketones represents an alternative to the Baeyer-Villiger oxidation or the Beckmann rearrangement under basic conditions. The method is suited for the transformation of natural products and enables access to orthogonally reactive dicarbonyl compounds.
Manipulating micellar environments for enhancing transition metal-catalyzed cross-couplings in water at room temperature
Lipshutz, Bruce H.,Ghorai, Subir,Leong, Wendy Wen Yi,Taft, Benjamin R.,Krogstad, Daniel V.
experimental part, p. 5061 - 5073 (2011/08/06)
The remarkable effects of added salts on the properties of aqueous micelles derived from the amphiphile PTS are described. Most notably, Heck reactions run in the presence of NaCl lead to couplings on aryl bromides in water at room temperature. Olefin cross- and ring-closing metathesis reactions run in the presence of small amounts of pH-lowering KHSO4 are also accelerated, another phenomenon that does not apply to typical processes in organic media. These salt effects allow, in general, for synthetically valuable C-C bond-forming processes to be conducted under environmentally benign conditions. Recycling of the surfactant is also demonstrated.
N-heterocycle carbene (NHC)-ligated cyclopalladated N,N- dimethylbenzylamine: A highly active, practical and versatile catalyst for the Heck-Mizoroki reaction
Peh, Guang-Rong,Kantchev, Eric Assen B.,Zhang, Chi,Ying, Jackie Y.
supporting information; experimental part, p. 2110 - 2119 (2009/09/05)
The wide dissemination of catalytic protocols in academic and industrial laboratories is facilitated by the development of catalysts that are not only highly active but also user-friendly, stable to moisture, air and long term storage and easy to prepare on a large scale. Herein we describe a protocol for the Heck-Mizoroki reaction mediated by cyclopalladN-dimethylbenzylamine (dmba) ligated ne, 1,3-bdot;HCl in refluxing acetonitrile in air in the presence of K2CO in iates the H bromides in reagent grade NMP at the 0.1-2 mol% range without the need for rigorous anhydrous techniques or a glovebox, and is active even in air. The catalyst is capable of achieving very high levels of catalytic activity (TON of up to 5.22 × 105) for the coupling of a deactivated arylbromide, p-bromoanisole, with tBu acrylate as a benchmark substrate pair. A wide range of aryl bromides, iodides and, for the first time with a NHC-Pd catalyst, a triflate was coupled with diverse acrylate derivatives (nitrile, tert-butyl ester and amides) and styrene derivatives. The use of excess (>2 equiv.) of the aryl bromide and tert-butyl acrylate leads to mixture of tert-butyl β,β-diarylacrylate and tert-butyl cinnamate derivatives depending on the substitution pattern of the aryl bromide. Electron rich m- and p-substituted arylbromides give the diarylated products exclusively, whereas electron-poor aryl bromides give predominantly mono-arylated products. For o-substituted aryl bromides, no doubly arylated products could be obtained under any conditions. Overall, the active catalyst (IMes-Pd) shows higher activity with electron-rich aryl halides, a marked difference compared with the more commonly used phosphane-Pd or non-ligated Pd catalysts.
Enantioselective sequential conjugate addition-allylation reactions: A concise total synthesis of (+)-podophyllotoxin
Wu, Yingming,Zhao, Jingfeng,Chen, Jingbo,Pan, Chengxue,Li, Ang,Zhang, Hongbin
supporting information; experimental part, p. 597 - 600 (2009/09/25)
(Chemical Equation Presented) A highly flexible and concise total synthesis of (+)-podophyllotoxin featured with an enantioselective sequential conjugate addition-allylation reaction was reported. Starting from commercially available 3,4,5-trimethoxycinna
Practical Heck-Mizoroki coupling protocol for challenging substrates mediated by an N-heterocyclic carbene-ligated palladacycle
Kantchev, Eric Assen B.,Peh, Guang-Rong,Zhang, Chi,Ying, Jackie Y.
supporting information; experimental part, p. 3949 - 3952 (2009/05/30)
(Chemical Equation Presented) A highly active, N-heterocyclic carbene-palladacycle precatalyst for the Heck-Mizoroki reaction was rationally designed. The complex can be synthesized on a large scale in excellent yield by a novel, one-pot, three-component reaction and is tolerant to air, moisture, and long-term storage. A wide range of challenging substrates is successfully coupled under a simple and user-friendly reaction protocol.
