Direct observation of acyl anion equivalents by carbon-13 Fourier transform nuclear magnetic resonance

Oakes, Fred T.; Sebastian, John F.

doi:10.1021/jo01312a027

Cited by 56 publications

(15 citation statements)

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“…In the current study, both the microsolvation model and the mixed discrete-continuum model seem better in reproducing the experimental results. It is well-known that vinylic lithiation is preferred experimentally for DHF and DHP, 8 Keywords: Density functional theory; Microsolvation; Continuum solvation; Mixed discrete-continuum solvation; Transition states. generally believed that both the electronegative vinyl ether oxygen and precomplexation affect lithiation regioselectivity.…”

Section: Introductionmentioning

confidence: 99%

Density functional study of the lithiation of cyclic vinyl ethers in solution

Yan

Sebastian

2004

Tetrahedron

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Section: Introductionmentioning

confidence: 99%

Density functional study of the lithiation of cyclic vinyl ethers in solution

Yan

Sebastian

2004

Tetrahedron

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“…The 1 Ha nd 13 C spectra of 1&THF in [D 8 ]THF at À60 8C, À80 8Cand À100 8Cdisplayed only one set of signals. In addition, the 1 J(C2,C3)c oupling is reduced in magnitudeb y2 7Hzasc ompared to that of 7.S imilar down-field shifts and/orr eductionso ft he magnitude of the coupling constant have been described for vinyllithium, [25][26][27] ethoxyvinyllithium, [28] halogen vinyllithiums [25] and aryl vinyllithiums. The variations in the chemical shifts of 1&THF on going from room temperature to low temperatures were only minor.F or example, the 13 CNMR signal of C2 experienced ah igh-field shift of Dd = À0.8 ppm, while the signal of C3 showed at emperaturedependentv ariation of Dd = À2ppm.…”

Section: Synthesis Of Vinyl Sulfoximinesmentioning

confidence: 86%

“…The variations in the chemical shifts of 1&THF on going from room temperature to low temperatures were only minor.F or example, the 13 CNMR signal of C2 experienced ah igh-field shift of Dd = À0.8 ppm, while the signal of C3 showed at emperaturedependentv ariation of Dd = À2ppm. [25][26][27][28][29][30] Thus, the p-bond of 1 is similarly polarized as in other vinyllithiums despite the presence of the sulfonimidoyl group. Thus, it is concluded that 1&THF exists in THF preferentially as am onomer on the basis of the NMR spectroscopic and cryoscopicresults.…”

Section: Synthesis Of Vinyl Sulfoximinesmentioning

confidence: 99%

Experimental and Computational Studies of the Structure of Sulfonimidoyl Vinyllithiums

Giesen

Raabe

Runsink

et al. 2017

Chemistry A European J

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tBuCH=C(Li)S(O)(NSO Tol)Ph⋅L (L=2THF, TMEDA) (1⋅L) in THF solution is a monomer with a C-Li bond according to NMR spectroscopy and cryoscopy. It was identified as CIP through the scalar C, Li coupling and Li,{ H} NOE experiments. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure. Li, H FUCOUP and Li, H HMQC NMR experiments of 1⋅TMEDA revealed a scalar Li, H coupling across the Li-C=C-H bonds. According to the NMR data the π-bond of 1⋅L is polarized by the negative charge of the anionic C atom. tBuCH=C(Li)S(O)(NMe)Ph (2⋅L) is most likely also a monomer with a C-Li bond. According to Li,{ H} NOE experiments it has a four-membered C-Li-N-S chelate ring structure. C NMR spectroscopy showed the C-Li bonds of 1⋅L and 2⋅L to be fluxional. H NMR spectroscopy and 1D TOCSY experiments of Ph C=C(Li)S(O)(NSO Tol)Ph revealed topomerization of the phenyl groups, which is attributed to a fast positional exchange of the Li atom and the sulfonimidoyl group. The fluxionality of the C-Li bond and the interchange of the Li atom and the sulfonimidoyl group at the anionic C atom of sulfonimidoyl vinyllithiums, which result in a low configurational stability, most likely involve the formation of O,Li and N,Li CIPs through heterolysis of the C-Li bond. Ab initio calculation of MeCH=C(Li)S(O)(NMe)Ph yielded an energy minimum structure with a C-Li bond, a four-membered C-Li-N-S chelate ring and a strongly expanded C=C-Li bond angle. According to calculation of MeCH=C(Li)S(O)(NMe)Ph, [MeCH=CS(O)(NMe)Ph] and MeCH=C(H)S(O)(NMe)Ph deprotonation is not accompanied by a shortening of the C-S bond. Ab initio calculation of MeCH=C(Li)S(O)(NSO Me)Ph gave a structure with a C-Li bond and a six-membered C-Li-O-S-N-S chelate ring. Li, H NOE experiments and cryoscopy of LiCH S(O)(NSO Tol)Ph (3) revealed a monomeric CIP with a C-Li bond. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure found in polymeric 3 in the crystal.

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“…The solvents were then removed completely, and the addition of pentane precipitated the crude product as a brown solid, which was recrystallized from toluene/pentane to give the required complex as a buff-coloured solid (50 mg, 35%). 1 Preparation of (2-2 H 1 )-2,3-Dihydrofuran by a Modified Procedure [28]. In a dry Schlenk tube, BuLi (2.5m in hexane, 13 ml) was added rapidly to a mixture of freshly distilled 2,3-dihydrofuran (2 g, 28.5 mmol) and tmeda (0.6 g), whereupon vigorous effervescence and precipitation occurred.…”

Section: Experimental Partmentioning

confidence: 99%

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

Hii

Claridge

Brown

et al. 2001

HCA

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Dedicated to the memory of Professor Luigi M. VenanziReactive intermediates in the asymmetric Heck reaction between aryl electrophiles and 2,3-dihydrofuran have been identified by NMR and mass spectrometry, with BINAP or the achiral diphosphanes dppp and dppf as ligands. The major cationic species observed is an alkylpalladium produced by addition of PdAr to the alkene followed by two further PdH-mediated isomerisation steps. This last species has been characterised at À 608 by 1 H-, 13 C-, and 31 P-NMR, including HMQC techniques. The regiochemistry of PdAr and PdH addition to the reactant are opposite as defined by the reaction with (2-2 H 1 )-2,3-dihydrofuran. DFT Calculations on the reaction pathway between [CH 2 (PH 2 )]PdPh and 2,3-dihydrofuran reveal several structurally interesting intermediates involving agostic b-H-atom, ipso-Ph or reactant O-atom bonded to the Pd-atom, and elucidate the isomerisation pathway.An interesting mechanistic sidelight emerged from the earliest reports of the specified Heck reaction (see [6] and earlier papers cited therein). Depending on the reaction conditions, the product was predominantly the 2,5-or 2,3-dihydro isomer 2 or 3, respectively, with excess PPh 3 providing the latter. This implies an intermediate that can partition between elimination and isomerisation. In the detailed studies carried out by Hayashi and co-workers, both were formed with the latter favored; the enantiomer excess (e.e.) of the major product was enhanced by a favorable partition of the diastereoisomers of the first-formed intermediate, minor towards elimination and major towards isomerisation [5]. Subsequently, Pfaltz and Loiseleur and co-workers demonstrated that catalysis involving a PN ligand in the phosphinoaryldihydrooxazole series provided entirely the 2,5-dihydroisomer in high e.e. [7]; other results obtained were broadly in line with a single double-bond-shift pathway. Subsequent workers have largely confirmed this regiochemical pattern, with diphosphine ligands giving rise mainly to double-isomerisation products and with phosphinamine ligands to singleisomerisation products.When this work was started, there were no detailed mechanistic studies on the asymmetric Heck reaction and, indeed, few on the reaction in general [8]. In the intervening period, there has been an effusion of speculations about the detailed mechanism of simple Heck reactions, especially on the role of Pd 0 ± Pd II vs. Pd II ± Pd IV cycles [9] 4 ), and the possible involvement of deligated colloidal Pd or Pd nanoparticles [10]. Direct evidence on the structure of true late intermediates in the catalytic cycle remains limited to the cationic-diphosphine case from our own work [1] [7] [11] and a related contribution from Akermark and co-workers [12]. There are related studies on alkene-Pd polymerisation or alkene/CO copolymerisation [13] in which comparable intermediates have been identified and characterised. Results and Discussion. ± Observation of Reactive Intermediates. In our original communication on this topic, the o...

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Direct observation of acyl anion equivalents by carbon-13 Fourier transform nuclear magnetic resonance

Cited by 56 publications

References 1 publication

Density functional study of the lithiation of cyclic vinyl ethers in solution

Density functional study of the lithiation of cyclic vinyl ethers in solution

Experimental and Computational Studies of the Structure of Sulfonimidoyl Vinyllithiums

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

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