Lithium-selenium exchange. Stereochemistry of .alpha.-lithio selenides and sulfides

Reich, Hans J.; Bowe, Michael D.

doi:10.1021/ja00180a062

Cited by 89 publications

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“…This fact indicates that the lithium species formed by in situ deprotonation is the same which survives after 3 h of deprotonation. However, the possibility that the alkyllithium species epimerizes before the reaction with electrophile could not be completely excluded 3d. Thus, from this experiment, question arises: why no evidence was found for the existence of the epimeric lithium compound epi ‐ 9 ?…”

Section: Resultsmentioning

confidence: 90%

Highly Diastereoselective Lithiation and Substitution of an (S)‐Prolinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate): Synthesis of Enantiomerically Pure Prolinethiols

Sonawane¹,

Mück‐Lichtenfeld²,

Fröhlich³

et al. 2007

Chemistry A European J

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Highly diastereoselective lithiation-substitution reactions of an (S)-proline derived S-alkyl thiocarbamate was accomplished. The configuration of the predominant alkyllithium species and the stereochemical course of the electrophilic substitution reactions are deduced by a combination of X-ray crystal structure analysis, NMR spectroscopic studies, deuteration/dedeuteration experiments, and quantum chemical calculations. The lithium intermediate (S,S)-9 was found to be kinetically and thermodynamically favoured, whereas (S,R)-9 rapidly epimerizes.

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Section: Resultsmentioning

confidence: 90%

Highly Diastereoselective Lithiation and Substitution of an (S)‐Prolinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate): Synthesis of Enantiomerically Pure Prolinethiols

Sonawane¹,

Mück‐Lichtenfeld²,

Fröhlich³

et al. 2007

Chemistry A European J

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“…The advantages of this method over the previously reported hydroselenation reactions are that diorganyl diselenides and selenol do not need to be previously prepared or handled. All compounds prepared were characterized by 1 H and 13 C NMR spectroscopy, and the structures of 5c and 5d were elucidated by X-ray crystallography, which indicated that the cyclization occurred via 6-endo-dig mode.…”

Section: Resultsmentioning

confidence: 99%

“…1 H NMR (400 MHz, CDCl 3 ): δ (ppm) 7.39-7.19 (m, 10H), 6.86 (d, J = 10.6 Hz, 1H), 6.62 (d, J = 10.6 Hz, 1H), 4.00 (s, 2H). 13…”

Section: (Z)-benzyl(styryl)selane (2a)mentioning

confidence: 99%

Stereoselective Synthesis of Z‐Vinyl Selenides Through the Reaction of Sodium Selenide with Organic Halides and Alkynes

2019

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A practical synthetic approach to the stereoselective synthesis of Z‐vinyl selenides is described through the reaction of sodium selenide with organic halides, followed by the addition to alkynes. The reaction conditions were also successfully applied to the synthesis of selenochromones through the intramolecular version of this methodology by the reaction of 2‐chlorophenylynones with sodium selenide. The synthetic utility of vinyl selenides prepared was proven through the reaction with Kumada, Negishi and Suzuki substrates, giving the corresponding cross‐coupled products in good yields.

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“…[17] We extended the method further by preparing the STIB cholesterol derivative 8,w hich upon exposure to the optimized reaction conditions gave 9 (ClCO 2 Me quench) in excellent yield and as asingle diastereoisomer (Scheme 7). [18] This example highlights two key features in the generation of nonstabilized, tertiary a-S-substituted organolithium intermediates under our conditions.1 )Although the Li atom adopts an equatorial position in Li-8,a no rientation that according to Beak [12] and Reich [19] will favor epimerization by forming the more stable configuration with an axially positioned lithium (where the bulky TIB group is placed at an equatorial position), epimerization was not observed, underscoring the remarkable configurational stability of nonstabilized tertiary a-S-substituted organolithium species generated under our conditions.2 )The kinetic acidity of the a-S-proton in STIB esters 4 and 8 is remarkably high and outcompetes the lithiation of the allylic position.…”

mentioning

confidence: 80%

Asymmetric Synthesis of Tertiary Alcohols and Thiols via Nonstabilized Tertiary α‐Oxy‐ and α‐Thio‐Substituted Organolithium Species

et al. 2017

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Nonstabilized a-O-substituted tertiary organolithium species are difficult to generate,and the a-S-substituted analogues are configurationally unstable.W en ow report that they can both be generated easily and trapped with arange of electrophiles with high enantioselectivity,p roviding ready access to ar ange of enantioenriched tertiary alcohols and thiols.T he configurational stability of the a-S-organolithium species was enhanced by using aless coordinating solvent and short reaction times.Chiral a-heteroatom (O,N ,a nd S)-substituted organolithium compounds are av ersatile class of nucleophiles that are useful in the asymmetric synthesis of chiral alcohols, amines,a nd thiols.[1] Although the use of secondary and mesomerically stabilized (e.g., benzylic and allylic) tertiary a-O-and a-S-substituted organolithium reagents in synthesis is well established, [1c-e] the use of non-mesomerically stabilized (i.e., dialkyl-substituted) tertiary reagents is not. This discontinuity is due to contrasting problematic features governing a-O-and a-S-substituted organolithium species. Nonstabilized tertiary a-O-organolithium compounds are configurationally stable but are difficult to generate owing to their reduced kinetic acidity (Scheme 1B); [1e, 2] tertiary a-Sorganolithium species are easily formed but are not configurationally stable (Scheme 1A). To apply a-O/S-substituted organolithium compounds in asymmetric synthesis,both ease of generation and configurational stability are essential requirements. [1a-d,3] Through variation of the directing group,b ase,s olvent, and additives we discovered reaction conditions enabling the stereospecific deprotonation of secondary dialkyl benzoates (TIB esters) [4] and demonstrated their configurational stability in lithiation-borylation reactions.[5] Herein, we report the broad applicability of these novel enantioenriched nucleophiles in reactions with ab road range of electrophiles.I n addition, we have discovered reaction conditions for the generation of enantioenriched, tertiary,n onstabilized a-Sorganolithium compounds and report their subsequent trapping with electrophiles in high enantioselectivity (Scheme 1C).Boronic esters represent an iche class of electrophiles, [6] and therefore,w ei nitially embarked on as tudy of the trapping of tertiary a-O-substituted organolithium species, which were generated by lithiation of the enantioenriched TIB esters 1a-1e,w ith ar ange of electrophile classes (Scheme 2). Upon exposure of av ariety of enantioenriched benzoates to sec-BuLi and TMEDAinCPME at À60 8 8C, the corresponding organolithium species Li-1a-1e were generated. Pleasingly,L i-1a-1e were successfully trapped with ar ange of electrophiles,i ncluding methyl chloroformate (2aa), benzoyl chloride (2ab), isocyanates (2ac and 2ad), aldehydes (2ae and 2af), and trialkyl tin chlorides (2ag, 2ah, 2ba-2ea). Reactions with aldehydes gave mixtures of diastereomers (see 2ae and 2af)b ut in the case of PhCHO,h igh Scheme 1. A, B) Previous studies regardingnonstabilized tert...

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Lithium-selenium exchange. Stereochemistry of .alpha.-lithio selenides and sulfides

Cited by 89 publications

References 0 publications

Highly Diastereoselective Lithiation and Substitution of an (S)‐Prolinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate): Synthesis of Enantiomerically Pure Prolinethiols

Highly Diastereoselective Lithiation and Substitution of an (S)‐Prolinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate): Synthesis of Enantiomerically Pure Prolinethiols

Stereoselective Synthesis of Z‐Vinyl Selenides Through the Reaction of Sodium Selenide with Organic Halides and Alkynes

Asymmetric Synthesis of Tertiary Alcohols and Thiols via Nonstabilized Tertiary α‐Oxy‐ and α‐Thio‐Substituted Organolithium Species

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