A convenient method for estimation of alkyllithium concentrations

Kofron, William G.; Baclawski, Leona M.

doi:10.1021/jo00872a047

Cited by 505 publications

(295 citation statements)

References 1 publication

Supporting

Mentioning

290

Contrasting

Unclassified

Order By: Relevance

“…t-Butyllithium and homoallyllithium were titrated with diphenylacetic acid. 80 The freshly prepared homoallylmagnesium bromide was titrated using benzyl alcohol and phenantrolin. 81 After preparation of the cuprates, a Gilman test using Michler´s ketone was carried out to make sure that no homoallyllithium or homoallylmagnesium bromide remained (Scheme 67 It is known that alkylcuprates are less stable than alkenylcuprates, which is due to their ability to undergo a β-hydride elimination.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Modular Asymmetric Synthesis of Functionalized Azaspirocycles Based on the Sulfoximine Auxiliary

et al. 2007

View full text Add to dashboard Cite

A modular asymmetric synthesis of the functionalized azaspirocycles 6 (m = 2, n = 1), 7 (m = 1, n = 2), 8 (m = n = 2), 12, 20, and 24 from the cyclic allylic sulfoximines 1 is described. The synthetic strategy is based on the stereoselective construction of the carbocycle 4 containing the amino-substituted tertiary C atom from 1 followed by the generation of the azaspirocycle. Three different routes have been followed for the synthesis of the heterocyclic ring: N,C-dianion cycloalkylation, ring-closing metathesis, and N-acyl iminium ion formation.

show abstract

Section: Resultsmentioning

confidence: 99%

“…80,81 NMR SPECTRA NMR spectra were recorded at room temperature using the following spectrometers: Varian VXR 300, Varian Inova 400, and Varian Unity 500.…”

Section: Reagentsmentioning

confidence: 99%

Modular Asymmetric Synthesis of Functionalized Azaspirocycles Based on the Sulfoximine Auxiliary

et al. 2007

View full text Add to dashboard Cite

show abstract

“…All solvents and reagents used were reagent grade and, when required, further purifications were accomplished following published procedures (21). Titrations of the organolithium reagents were done using diphenylacetic acid (22). 2 To a solution of dry (R)-pantolactone (1) (2.00 g, 15.4 mmol) in dichloromethane (40 mL) was added biethylamine (2.69 mL, 19.3 mmol'), tert-butyldimethylsilyl chloride (2.79 g, 18.5 mmol), and DMAP (0.39 g, 3.2 mmol).…”

Section: Methodsmentioning

confidence: 99%

Controlled diastereoselection in 2-lithio-1,3-dithiane additions onto α-substituted γ-lactols. Model studies toward bryostatins from (R)-pantolactone

Roy¹,

Rey²

1991

Can. J. Chem.

View full text Add to dashboard Cite

RENB ROY and ALLAN W. REY. Can. J. Chem. 69, 62 (1991). Homochiral a-substituted y-lactols 3 and 4 derived from (R)-pantolactone 1 were used in 2-lithio-1,3-dithiane additions to afford very high controls in diastereoselectivities arising from 1,2-asymmetric inductions. Thus non-chelation controlled nucleophilic addition on 3 gave the anti diastereomer 5 as the major product (92% de), while the chelation controlled addition on 4 furnished the syn diastereomer 7 (96% de) as the almost exclusive product. The stereochemical outcomes of these reactions were proven unambiguously by locking the conformation of the syn-and anti-trio1 adducts 7 and 8 through their respective acetonides and by nuclear Overhauser enhancement measurements. The lack of 1,3-dioxolane formation in the case of the anti-trio1 8 was taken as a further confirmation of the absolute configuration at the newly created stereocenter.Key words: byrostatin, pantolactone, a-hydroxylactol, dithiane.RENB ROY et ALLAN W. REY. Can. J. Chem. 69, 62 (1991). Les y-lactols homochirals 3 et 4 a-substituts dtrivts de la (R)-pantolactone 1 ont Ctt utilisCs dans des rtactions d'additions avec le carbanion lithit du 1,3-dithiane pour fournir un trks haut contr6le diasttrtostlectif provenant d'une induction asymttrique-1,2. Le sttrtocontr6le de I'addition nucltophilique sur 3 en l'absence de phtnomkne de chtlatation a donne le diastertomkre anti 5 c o m e produit majeur tandis que la chtlatation cornrne moyen de sttrtocontr6le de I'addition nucltophilique sur 4 a conduit presque exclusivement au diasttrtomkre syn 7 c o m e produit final. Les rtsultats sttriochimiques de ces rtactions ont t t t prouvts de f a~o n non-ambigiie en fixant la conformation des adduits syn-et anti-trio1 7 et 8 par la formation de leurs dtrivts acttals respectifs et par des mesures d'effets nOe. L'absence de formation de 1,3-dioxolane dans le cas du triol-anti 8 a t t i considtrte comme preuve suppltmentaire de la configuration absolue au nouveau centre sttrtogtnique form6 .Mots cle's : byrostatine, pantolactone, a-hydroxylactol, dithiane. IntroductionDuring synthetic endeavors (1-3) toward the construction of the antineoplastic macrolides bryostatins (4), chiral fragments containing quaternary gem-dimethyl carbon centers were required. Within the chiral pool, (R)-pantolactone 1 was sought as a useful chiral template. As such, 1 has scarcely been utilized for the enantiomeric synthesis of complex natural products (5, 6). On the other hand, 1 and its (S)-enantiomer (7) have received increased interest as chiral auxiliaries in asymmetric Diels-Alder cycloadditions (7,8) and in diastereoselective ketene protonations (9).Although there have been numerous examples of 1,2-induction in acyclic stereoselections (lo), examples of similar or remote inductions in y-or 6-lactols have received limited attention (1 1). We wish to describe herein the results obtained with 2-lithio-l,3-dithiane additions onto a-substituted y-lactols. The effects of 1,2-chelation and non-chelation on the diastereoselectivitie...

show abstract

“…8,9 preparation of 3,5-dimethylisoxazole (5) 10 A solution of hydroxylamine hydrochloride (8.34 g, 0.12 mole) in water (10 ml) was added a solution of 2,4-pentanedione (6) (10.2 g, 0.1 mole) in ethanol (10 ml). The mixture was heated under reflux temperature for 3 hours, then allowed to cool to room temperature and poured into cold water (60 ml).…”

Section: Experimental Section Generalmentioning

confidence: 99%

Reductive ring opening of 3,5-bis(2-arylethenyl)isoxazoles with molybdenum hexacarbonyl: A novel route to symmetrical and unsymmetrical curcumin derivatives

Hahnvajanawong

Thaima²,

Tearavarich³

et al. 2016

Orient. J. Chem

View full text Add to dashboard Cite

Curcumin derivatives were successfully synthesized from 3,5-dimethylisoxazole by lateral metalation and condensation with various aromatic aldehydes sequentially at C 5 -and C 3 -methyl groups. After dehydration, further transformation of isoxazole ring to b-diketone moiety was accomplished by reductive ring opening using molybdenum hexacarbonyl [Mo(CO) 6 ] and subsequent simple acidic hydrolysis.

show abstract

A convenient method for estimation of alkyllithium concentrations

Cited by 505 publications

References 1 publication

Modular Asymmetric Synthesis of Functionalized Azaspirocycles Based on the Sulfoximine Auxiliary

Modular Asymmetric Synthesis of Functionalized Azaspirocycles Based on the Sulfoximine Auxiliary

Controlled diastereoselection in 2-lithio-1,3-dithiane additions onto α-substituted γ-lactols. Model studies toward bryostatins from (R)-pantolactone

Reductive ring opening of 3,5-bis(2-arylethenyl)isoxazoles with molybdenum hexacarbonyl: A novel route to symmetrical and unsymmetrical curcumin derivatives

Contact Info

Product

Resources

About