Aufbau von asymmetrischen quartären Kohlenstoffzentren mit hoher Enantioselektivität

Shimizu, Masaki

doi:10.1002/ange.201101720

Cited by 26 publications

(6 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[2] Synthetic studies on these special units have been extensively carried out in recent years. [1] Although many methods are available for the synthesis of quaternary carbon centers, [1] it is highly desirable to develop alternative methods that could be advantageous in terms of functional-group tolerance, operational simplicity, and the use of readily available and stable starting materials.…”

mentioning

confidence: 99%

Palladium‐Catalyzed Divergent Reactions of α‐Diazocarbonyl Compounds with Allylic Esters: Construction of Quaternary Carbon Centers

et al. 2011

View full text Add to dashboard Cite

Take two: α‐Diazocarbonyl compounds display a diverse pattern of reactivity upon palladium‐catalyzed reaction with esters. Esters bearing an alkynyl group on the carbonyl carbon atom lead to two different CC bonds at the same carbon atom in a single operation through decarboxylation and migratory insertion, whereas aromatic and benzylic acid derivatives afford aromatic and benzylic esters bearing an O‐substituted quaternary carbon center.

show abstract

mentioning

confidence: 99%

Palladium‐Catalyzed Divergent Reactions of α‐Diazocarbonyl Compounds with Allylic Esters: Construction of Quaternary Carbon Centers

et al. 2011

View full text Add to dashboard Cite

show abstract

“…[44] The triflyl group is an excellent nucleofuge, [45] and the alkylation of (S)-41 with organometallics might be facilitated by their possible prior coordination to the methoxy group. [44] The triflyl group is an excellent nucleofuge, [45] and the alkylation of (S)-41 with organometallics might be facilitated by their possible prior coordination to the methoxy group.…”

Section: Racemization Of Salts [R 1 C(r 2 )-mentioning

confidence: 99%

Chiral Fluorinated α‐Sulfonyl Carbanions: Enantioselective Synthesis and Electrophilic Capture, Racemization Dynamics, and Structure

Hellmann

Hack

Thiemermann

et al. 2013

Chemistry A European J

View full text Add to dashboard Cite

Enantiomerically pure triflones R(1) CH(R(2) )SO2 CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3 Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3 SSCF3 . The deprotonation of RCH(Me)SO2 CF3 (R=CH2 Ph, iHex) with nBuLi with the formation of salts [RC(Me)SO2 CF3 ]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2 CF3 group of (S)-MeOCH2 C(Me)(CH2 Ph)SO2 CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2 C(Me)(CH2 Ph)Et of 96 % ee. Racemization of salts [R(1) C(R(2) )SO2 CF3 ]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα S bond rotation as the rate-determining step. Lithium α-(S)-trifluoromethyl- and α-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH2 C(Me)SO2 tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105 °C of 2.4 h, that of [PhCH2 C(Me)SO2 CF3 ]Li at -78 °C is 30 d. DNMR spectroscopy of amides (PhCH2 )2 NSO2 CF3 and (PhCH2 )N(Ph)SO2 CF3 gave NS rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2 C(Ph)SO2 R]M (M=Li, K, NBu4 ; R=CF3 , tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2 C(Ph)SO2 CF3 ]Li⋅L}2 (L=2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2 C(Ph)SO2 CF3 ]NBu4 have the typical chiral Cα S conformation of α-sulfonyl carbanions, planar Cα atoms, and short Cα S bonds. Ab initio calculations of [MeC(Ph)SO2 tBu](-) and [MeC(Ph)SO2 CF3 ](-) showed for the fluorinated carbanion stronger nC →σ* SCF 3 and nO →σ* SCF 3 interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R(1) C(R(2) )SO2 R](-) (R=tBu, CF3 ) the nC →σ*SR interaction is much stronger for R=CF3 . Ab initio calculations gave for [MeC(Ph)SO2 tBu]Li⋅2 Me2 O an O,Li,Cα contact ion pair (CIP) and for [MeC(Ph)SO2 CF3 ]Li⋅2 Me2 O an O,Li,O CIP. According to cryoscopy, [PhCH2 C(Ph)SO2 CF3 ]Li, [iHexC(Me)SO2 CF3 ]Li, and [PhCH2 C(Ph)SO2 CF3 ]NBu4 predominantly form monomers in tetrahydrofuran (THF) at -108 °C. The NMR spectroscopic data of salts [R(1) (R(2) )SO2 R(3) ]Li (R(3) =tBu, CF3 ) indicate that the dominating monomeric CIPs are devoid of Cα Li bonds.

show abstract

“…Stereoselective access to these centers remains an important challenge in organic synthesis. [13] At first, the two reactions were conducted separately in order to determine the most compatible conditions. The first reaction is a 1,4 reduction of carvone by a preformed copper(I) hydride [14] to generate the silyl enolate in situ.…”

mentioning

confidence: 99%

Copper/Palladium‐Catalyzed 1,4 Reduction and Asymmetric Allylic Alkylation of α,β‐Unsaturated Ketones: Enantioselective Dual Catalysis

et al. 2013

View full text Add to dashboard Cite

Vereinte Kräfte: Die Kupplung zweier metallorganischer Intermediate gelingt über eine duale Cu/Pd‐Katalyse (siehe Schema, LG=Abgangsgruppe), bei der CuI katalytisch das Ausgangsmaterial für den Pd0‐Katalysezyklus bereitstellt. Obwohl die Reagentien in stöchiometrischen Mengen in der Reaktionsmischung vorhanden sind und beide aktiven Intermediate abfangen könnten, verläuft die erwünschte Reaktion wie geplant.

show abstract

Aufbau von asymmetrischen quartären Kohlenstoffzentren mit hoher Enantioselektivität

Cited by 26 publications

References 28 publications

Palladium‐Catalyzed Divergent Reactions of α‐Diazocarbonyl Compounds with Allylic Esters: Construction of Quaternary Carbon Centers

Palladium‐Catalyzed Divergent Reactions of α‐Diazocarbonyl Compounds with Allylic Esters: Construction of Quaternary Carbon Centers

Chiral Fluorinated α‐Sulfonyl Carbanions: Enantioselective Synthesis and Electrophilic Capture, Racemization Dynamics, and Structure

Copper/Palladium‐Catalyzed 1,4 Reduction and Asymmetric Allylic Alkylation of α,β‐Unsaturated Ketones: Enantioselective Dual Catalysis

Contact Info

Product

Resources

About