Asymmetric Solvent Catalysis; <i>N,N,N</i>′,<i>N</i>′‐Tetramethyl‐2,3‐dimethoxy‐1,4‐butanediamine, a New Chiral Medium

Seebàch, Dieter; Dörr, H.; Bastani, Bahram; Ehrig, Volker

doi:10.1002/anie.196909821

Cited by 48 publications

(11 citation statements)

References 11 publications

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“…This observation supported the view that reduction occurred only in cages containing the chiral inductor. Had there been intermolecular reduction (to yield racemic products) in cages that do not contain the chiral inductor the ee would have increased with increased loading levels of the chiral inductor While the ee obtained in this study is the highest amongst the thus far reported examples of photoreduction of achiral ketones, 19 unfortunately we are unable to develop a model that could be used to predict the extent of chiral induction within a zeolite. Several observations suggest that one must include the alkali ion in any mechanistic understanding of the asymmetric induction process within zeolites.…”

Section: Discussionmentioning

confidence: 67%

“…One of the earliest reports of the use of amines as chiral reagents is by Seebach and coworkers in the solution phase photopinacolization of aromatic ketones. 19 A mixture of 1 : 5 chiral amine to pentane as solvent at −72 • C gave about 23.5% ee in the DL-pinacol formed from acetophenone. It is important to note that in our studies no pinacol was obtained and in the majority of the cases the only product is the corresponding alcohol and the ee obtained within zeolites is in the range between 22-68%.…”

Section: Discussionmentioning

confidence: 99%

“…GC-MS (EI): 266 (M + , 7), 247 (1), 151 (19), 143 (20), 129 (12), 128 (88), 123 (100), 115 (22), 95 (35), 89(3), 75 (5).…”

Section: Experimental (A) Materialsunclassified

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Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

et al. 2006

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Photochemistry of 17 aryl alkyl ketones included within cation exchanged zeolites has been examined. In solution five of the 17 ketones undergo intramolecular hydrogen abstraction reaction even in the presence of a chiral amine and the rest are photoreduced to the corresponding alcohol. Within zeolites all 17 ketones yielded in presence of a chiral amine, the corresponding alcohol as the major product. When a chiral amine was used as the coadsorbent within alkali ion exchanged zeolites, enantiomerically enriched alcohol was formed in all cases. The best chiral induction was obtained with phenyl cyclohexyl ketone (enantiomeric excess: 68%). 1H-13C Cross Polarization Magic Angle Spinning (CP-MAS) experiments, with a model ketone (perdeuterated acetophenone) and chiral amine (pseudoephedrine) included within MY zeolites, suggested that the cation brings the reactant and the chiral amine closer. The role of the cation in such a process is also revealed by the computation results. The results presented here highlight the importance of a supramolecular structure in forcing a closer interaction between a reactant and a chiral inductor that could be used to achieve asymmetric induction in photoproducts.

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Section: Discussionmentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

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Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

et al. 2006

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“…A low enantioselectivity (6% ee) is obtained, even when an excess of L7 (3 equiv) is employed in the reaction. 20…”

Section: Scheme 4 Enantioselective Addition Of Grignard Reagents To mentioning

confidence: 99%

Catalytic Synthesis of Enantiopure Chiral Alcohols via Addition of Grignard Reagents to Carbonyl Compounds

et al. 2016

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“…Organolithium compounds are frequently used in organic syntheses as strong bases for lithiations and as powerful nucleophiles for C–C bond formations . Despite the fact that n -butyllithium ( n- BuLi) and other organolithium compounds are extensively employed reagents, comparatively few chirally modified organolithium complexes have been structurally characterized. , Structural analyses of enantiopure n- BuLi aggregates in solution − and in the solid state ,,− can provide explanations for reactivities and selectivities . Structural elucidations of these aggregates can also be crucial for a more rational design of new and more efficient chiral organolithium compounds for asymmetric syntheses .…”

Section: Introductionmentioning

confidence: 99%

Enantiopure Methyl- and Phenyllithium: Mixed (Carb-)Anionic Anisyl Fencholate-Aggregates

2019

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Methyl-and phenyllithium aggregates with enantiopure anisyl fencholate units form after reaction of organolithium reagent with (+)-anisyl fenchol in hydrocarbon and some ethereal solvents. These carbanionic aggregates are characterized by X-ray crystal analyses and exhibit both 3:1 stoichiometry and distorted cubic Li 4 O 3 C 1 cores, in which three lithium ions coordinate the carbanion (i.e., methylide or phenylide). These three lithium ions define a Lewis acidic surface (Li 3 ), binding the carbanion and expanding with the steric demand of the carbanion (i.e., from Me: 2.62 Å 2 , over n-Bu: 2.65 Å 2 (previous work) to Ph: 2.79 Å 2 ). Methylation and phenylation reactions of various prochiral aldehydes employing these methyllithium and phenyllithium aggregates yield alcohols with up to 44% ee. To rationalize the formation of the mixed (carb-)anionic aggregates, aggregate formation energies, describing co-condensations of RLi (R = Me, Ph, n-Bu) and lithium fencholates, are computed for the 3:1 and 2:2 stoichiometries. These computed aggregate formation energies point to preferences for 3:1 over 2:2 aggregates, as it is also apparent from experimental aggregate formations, confirmed by X-ray crystal analyses. In close analogy to the X-ray crystal structures, the computed Li 3 surfaces increase with increasing steric demand of the carbanions. The chiral, mixed (carb-)anionic RLi-fencholate aggregates hence adapt to different carbanion sized and arise not only with small (Me) or primary carbanions (n-Bu) but even with the larger secondary phenyl anion.

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Asymmetric Solvent Catalysis; N,N,N′,N′‐Tetramethyl‐2,3‐dimethoxy‐1,4‐butanediamine, a New Chiral Medium

Abstract: Conversion into the diamide (3b) .0 OC; [ a ]~ = 42.7 (c = 3.0 in CzH50H)], esterification to give (3c) [(CH&S04, m.p.

Cited by 48 publications

References 11 publications

Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

Catalytic Synthesis of Enantiopure Chiral Alcohols via Addition of Grignard Reagents to Carbonyl Compounds

Enantiopure Methyl- and Phenyllithium: Mixed (Carb-)Anionic Anisyl Fencholate-Aggregates

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