Asymmetric Synthesis of α‐Substituted Ketones by Metalation and Alkylation of Chiral Hydrazones

Lithium and magnesium enolates of cyclohexanone undergo palladium-catalyzed allylic alkylations under mild conditions. Diastereoselectivity and enantioselectivity are observed when the diphenyland dimethyl-substituted allylic substrates 1a and 1b are reacted with cyclohexanone or ethyl mesityl ketone. The lithium enolates of cyclohexanone, cyclopentanone and a-tetralone lead to the alkylations products 12-14 in an enantioselective manner. Axially chiral biphenyl-and binaphthyl-bisphosphanes provide high enantioselectivity and/or diastereoselectivity. In the case of the lithium enolates, the presence of lithium chloride is also crucial to reactivity and stereoselectivity. The stereochemical outcome of the allylic alkylation of cyclohexanone and acetophenone has been investigated by the palladium-catalyzed reaction of their lithium enolates with the cis/ trans isomeric alkenes (Z)-18 and (E)-19. It turns out that the preformed, non-stabilized enolates attack pallyl-palladium complexes generated in situ from the face opposite to the noble metal thus following the stereochemical pathway of soft, stabilized carbanions.

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“…[15] In addition, the CD spectrum of (R)-12, displayed a significant positive Cotton effect at 285 nm, again in agreement with known data.…”

Section: Introductionsupporting

confidence: 86%

Palladium‐Catalyzed Diastereoselective and Enantioselective Allylic Alkylations of Ketone Enolates

et al. 2008

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“…Shortly thereafter, Enders developed a very successful approach to the synthesis of enantiomerically pure compounds based on the reactions of chiral N,N-dialkylhydrazones made from carbonyl compounds and prolinol-derived chiral hydrazines known as SAMP and its enantiomer RAMP ( Figure 2). 1,2,48,49,[81][82][83][84] Other chiral hydrazines shown in Figure 2 were developed later for specific purposes.…”

Section: Short History Of Synthetic Applicationsmentioning

confidence: 99%

N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

2009

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“…In particular the hydrazones are much-used in chemical synthesis, e.g. as an intermediate for the Wolff-Kishner reduction [5,6] or the stereoselective alkylation [7] of a carbonyl compound. Arylhydrazones [8], especially 2,4-dinitrophenylhydrazones [9], are usually solids and are commonly employed for analytical separation and identification of carbonyls or other colorimetric sensing [10].…”

Section: Introductionmentioning

confidence: 99%

Influence of different aryl substitution on the crystal structures of benzil monohydrazone and dibenzil azine parent compounds

et al. 2011

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A series of benzil monohydrazones (1a, 1d) and corresponding dibenzil azines (2a-2d) featuring different p-aryl substituents have been synthesized and studied in regard of their crystal structures. Configurational and conformational properties as well as non-covalent interaction and packing behaviour of the molecules connected with the different substitution are discussed. The dibenzil azine 2a was found as a polymorph with reference to a known crystal structure.

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Asymmetric Synthesis of α‐Substituted Ketones by Metalation and Alkylation of Chiral Hydrazones

Cited by 80 publications

References 7 publications

Palladium‐Catalyzed Diastereoselective and Enantioselective Allylic Alkylations of Ketone Enolates

Palladium‐Catalyzed Diastereoselective and Enantioselective Allylic Alkylations of Ketone Enolates

N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

Influence of different aryl substitution on the crystal structures of benzil monohydrazone and dibenzil azine parent compounds

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