Asymmetric Fluorination of Enolates with Nonracemic <i>N</i>-Fluoro-2,10-Camphorsultams

Davis, Franklin A.; Zhou, Ping; Murphy, Christian; Sundarababu, G.; Qi, Hongyan; Han, Wei; Przeslawski, Robert M.; Chen, ‡ and Bang-Chi; Carroll, Patrick J.

doi:10.1021/jo972045x

Cited by 100 publications

(43 citation statements)

References 70 publications

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“…We suggested rather that the axial orientations observed in their X-ray analyses could mainly result from either an intermolecular H-bond for 4a (NÀH ¥¥¥¥¥ OS) 6 ) or external forces such as solidÀsolid packing interactions for 4b [20]. We also refuted his argument by giving the example of the N-fluoro sultam 1c, which exists in both pseudo-axial/equatorial conformations, as shown by 19 F-NMR analyses [4], thus leading us to suggest a more modest anomeric stabilization, estimated as 1.5 kcal/mol [16]. Furthermore, based on DFT calculations with BeckeÀPerdew functionals and DN** polarization basis set [21], we also suggested that their rigidified six-membered-ring sultam 4b should, in solution, exist as Helvetica Chimica Acta ± Vol.…”

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“…Although reduced by the electronegativity of the halogen, the Nfluoro analogues 1c and 1d show the same stereoelectronic features. Noteworthy are the conformational energies of both thermodynamically more stable pseudo-equatorial N-fluoro sultams, in line with the values expected from their respective 19 F-NMR [4] [3] or X-ray 13 ) analyses. Due to the absence of a pseudo-equatorial SO functionality, the case of sulfinamide 2a is peculiar.…”

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confidence: 96%

“…On their side, King et al [17] also invoked an anomeric effect, estimated between 2.0 and 2.5 kcal/mol. They based their rationalization on a stereoelectronic stabilization of the N lp with either the anti-periplanar, electronically deficient SÀC s* [18] or the vacant S d orbitals [19], which favors bisection of the OSO angle by the N lp 4 ). We now wish to report more details to compare these two opposite hypotheses, based on calculations at a higher ab initio level as well as conformational IR/Raman analyses of 4b.…”

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Comparative Infrared, Raman, and Natural‐Bond‐Orbital Analyses of King's Sultam

Hagemann

Dułak

Wesołowski

et al. 2004

Helvetica Chimica Acta

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Dedicated to Dr. G¸nther Ohloff on the occasion of his 80th anniversary By means of 1 H-NOESY-and Raman-spectroscopic analyses, we experimentally demonstrated the presence of the equatorial NÀMe conformer of King×s sultam 4b in solution, resulting from a rapid equilibrium. As a consequence, the value of the N lone-pair anomeric stabilization should be revised to 1.5 ± 1.6 kcal/mol. Independently from the N tilting, natural bond orbital (NBO)-comparative analyses suggest that the S d* orbitals do not appear as primordial and stereospecific acceptors for the N lone pair. Second, the fivemembered-ring sultams do not seem to be particularly well-stabilized by the SÀC s* orbital in the N-substituted pseudo-axial conformation, as opposed to an idealized anti-periplanar situation for the six-membered-ring analogues. In this latter case, the other anti-periplanar CÀC s* and C(1')ÀH/C(2') s*orbitals are as important, if not more, when compared to the SÀC s* participation. In the pseudo-equatorial conformation, g-sultams particularly benefit from the N lone-pair hyperconjugation with the anti-periplanar SÀO 1 s* and C(2)ÀH/C or C(1')ÀH/C s* orbitals. This is also the case for d-sultams when the steric requirement of the N-substituent exceeds 1.6 kcal/mol. When both axial and equatorial conformations are sterically too exacting, the N-atom is prone to sp 2 hybridization or/and conformational changes (i.e., 12c). In that case also, the mode of stereoelectronic stabilization differs from g-to d-sultams.Introduction. ± Based on semi-empirical calculations, we proposed in [1] that the steric origin of the diastereoselectivity imparted to N-a,b-enoyl derivatives by g-sultam auxiliaries of type 1 2 ) and 2 [6], as rationalized by Kim and Curran [7], is modulated by the stereoelectronic influence of the N lone pair (lp). We stressed that this additional effect, which is, under unchelating conditions, either matching or mismatching the steric approach, depending on the syn-or anti-s-cis conformations of the N-a,b-enoyl side chain, results from a general anomeric influence [8] 3 ) of the N lp, through the sp 2 CO, on the LUMO p-facial electronic distribution of the reactive centers. The N lp is itself orientated by stabilization with the anti-periplanar SÀO 1 s* orbital. We later

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Comparative Infrared, Raman, and Natural‐Bond‐Orbital Analyses of King's Sultam

Hagemann

Dułak

Wesołowski

et al. 2004

Helvetica Chimica Acta

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“…Controlling the α-stereochemistry through a carbon–carbon bond forming reaction could accomplish the equivalent of an asymmetric fluorination of a ketone, 47 a challenging transformation. Nakamura detailed the use of the tert -butyl PHOX ligand ( L-II ), while Tunge compared the PHOX ligand with another P,N-ligand, ( S )-QUINAP ( L-VI , Chart 9).…”

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Transition Metal-Catalyzed Decarboxylative Allylation and Benzylation Reactions

et al. 2011

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“…Very recently, Canadian authors, based on the X-ray analysis of a racemic six-membered-ring sultam, estimated the influence of the anomeric stabilization to 2.0 kcal/mol [26]. For the X-ray analysis of a N-fluorobornane-10,2-sultam, see [27].…”

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