Determination of the stereochemistry of γ‐Butyrolactones by DPFGSE‐NOE experiments

Xie, Xiulan; Tschan, Serena; Glorius, Frank

doi:10.1002/mrc.1965

Cited by 4 publications

(2 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Reaction of the cyclohexyl derivatives ( 27 and 29 , Scheme ) with TfOD also gave the d 1 ‐lactones ( d 1 ‐28 , d 1 ‐30a , and d 1 ‐30b )20,21 with relatively high deuterium incorporation [MS analysis also revealed some d 0 and d 2 products (46–50 %, d 1 ; 24–36 %, d 2 )22 as in the case of the allyl derivatives] 17. Although analysis of lactone d 1 ‐28 was difficult due to overlap of the key 1 H NMR signals, analysis of d 1 ‐30 revealed partial deuteration in both positions, cis and trans to the oxygen atom in both isomers.…”

Section: Resultsmentioning

confidence: 99%

Triflic Acid Mediated Dealkylative Lactonisation via NMR‐Observable Alkyloxonium Intermediates

Muñoz

Lloyd‐Jones

2009

Eur J Org Chem

View full text Add to dashboard Cite

Trifluoromethanesulfonic acid (TfOH) efficiently induces the dealkylative cyclisation of pent-4-enoates to generate ?-lactones with high selectivity. For primary alkyl esters bearing an additional alkene, only monolactonisation occurs, even in the presence of excess TfOH. The kinetics of the reaction have been studied by 1H NMR spectroscopy, which reveal that the TfOH acid undergoes a self-catalysed reaction with the pent-4-enoate to generate an oxonium triflate intermediate (rate ˜ kobsd.[TfOH]2[ester]1), possibly via the dimer (TfOH)2. The oxonium triflate intermediate then evolves to the ?-lactone according to unimolecular kinetics, liberating MeOTf in an SNi reaction. 2H-labelling experiments with TfOD suggest that the acid protonates the carbonyl moiety of the ester, with subsequent intramolecular delivery of D+ to the alkene. The resulting carbocation is transient, being rapidly captured intramolecularly to generate the oxonium species. Reversibility in this step mediates equilibration of diastereomeric oxonium intermediates via the carbocation

show abstract

Section: Resultsmentioning

confidence: 99%

Triflic Acid Mediated Dealkylative Lactonisation via NMR‐Observable Alkyloxonium Intermediates

Muñoz

Lloyd‐Jones

2009

Eur J Org Chem

View full text Add to dashboard Cite

show abstract

“…While it plays an important role in the NMR structure of biomacromolecules,16 it is well-known that NOE is a powerful tool in structural and conformational analysis of small molecules 17. For example, one of us has successfully applied selective NOEs to determine the stereochemistry of γ-butyrolactones 18. For studies on the stereochemistry of ruthenium complexes Kelso et al used 1 H, COSY, and NOE experiments to characterize the diastereoisomers of azobis(2-pyridine)-bridged bis(heteroleptic) diruthenium complexes in the meso and racemic forms 19.…”

Section: Resultsmentioning

confidence: 99%

Strategy for the Stereochemical Assignment of Tris-Heteroleptic Ru(II) Complexes by NMR Spectroscopy

2008

View full text Add to dashboard Cite

The relative stereochemistry of tris-heteroleptic ruthenium complexes [Ru(pp)(pp′)(pp″)](PF 6 ) 2 , where pp = 1,10-phenanthroline-4-carboxamide, pp′ = 5,6-dimethyl-1,10-phenanthroline, and pp″ = 7,8-dimethyl dipyrido[3,2-a:2′,3′-c]phenazine, was studied using NMR spectroscopy. The 1 H and 13 C spectra were assigned by using (DQF)-COSY, HSQC, and HMBC experiments for the two diastereomers, each a pair of enantiomers. NOE contacts between the neighboring ligands differentiated the two halves of each symmetrical ligand, thus enabling a full assignment of the NMR signals and an accurate determination of the relative stereochemistry of the complexes. Introduction of an additional chiral center to ligand pp by coupling it with L-lysine caused removal of the enantiomerism. Thus four diastereomers were observed and their relative stereochemistry determined.

show abstract

Diastereoselective Synthesis of Trifluoromethylated γ‐Butyrolactones via N‐Heterocyclic Carbene‐Catalyzed Conjugated Umpolung of α,β‐Unsaturated Aldehydes

2008

View full text Add to dashboard Cite

Abstract:The N-heterocyclic carbene-catalyzed conjugate umpolung of differently substituted a,bunsaturated aldehydes is described. Coupling of these compounds with a variety of trifluoromethylated ketones results in the selective formation of fluorinated g-butyrolactones. Using thiazolium-derived N-heterocyclic carbenes, the unlike stereoisomers are formed predominantly, whereas the imid-A C H T U N G T R E N N U N G azol-2-ylidene IMes results in lower selectivities and the preferred formation of the like isomer.Keywords: g-butyrolactones; N-heterocyclic carbenes; organocatalysis; organofluorine compounds; trifluoromethyl substitution; umpolung The inversion of polarity (umpolung) of electrophilic substrates by addition of nucleophilic catalysts is a versatile and synthetically useful concept in organic chemistry. Recently, the N-heterocyclic carbene [1] (NHC)-catalyzed, [2] chemo-and stereoselective umpolung of a,b-unsaturated aldehydes was developed, giving access to b- [3] and g-butyrolactones, [3,4] bicyclob-lactams, [5] g-lactams, [6] and cyclopentene derivatives. [7,8] The proposed mechanism for the formation of g-butyrolactones proceeds through a conjugate enamine, which represents a homoenolate equivalent (Scheme 1). The intermediates of the catalytic cycle could be validated by ESI-MS experiments.[4d]In our original publication, [4c] we reported the IMes-catalyzed conjugate umpolung of a,b-unsaturated aldehydes and the use of a,a,a-trifluoroacetophenone as the electrophilic reaction partner. This resulted in the formation of trifluoromethylated g-butyrolactones, albeit, with low diastereoselectivities.Fluorinated organic compounds have found widespread applications as active ingredients in drugs or crop protection agents, as materials or in catalysis [9] Scheme 1. Formation of g-butyrolactones by conjugate umpolung.

show abstract

Determination of the stereochemistry of γ‐Butyrolactones by DPFGSE‐NOE experiments

Cited by 4 publications

References 33 publications

Triflic Acid Mediated Dealkylative Lactonisation via NMR‐Observable Alkyloxonium Intermediates

Triflic Acid Mediated Dealkylative Lactonisation via NMR‐Observable Alkyloxonium Intermediates

Strategy for the Stereochemical Assignment of Tris-Heteroleptic Ru(II) Complexes by NMR Spectroscopy

Diastereoselective Synthesis of Trifluoromethylated γ‐Butyrolactones via N‐Heterocyclic Carbene‐Catalyzed Conjugated Umpolung of α,β‐Unsaturated Aldehydes

Contact Info

Product

Resources

About