Radiation chemical production, lifetimes, and structure-activity relations for .alpha.-dialkoxyalkyl carbocations in aqueous solutions:  Importance of solvation for cation reactivity

McClelland, Robert A.; Steenken, S.

doi:10.1021/ja00225a042

Cited by 25 publications

(10 citation statements)

References 3 publications

(3 reference statements)

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“…The quantitative alkyl order observed with the oxocarbocations was interpreted in terms of a polar effect rather than a steric one. 36, 37 The same conclusion is reached here. The polar constants σ* are 0.00 (Me), Ϫ0.10 (Et), Ϫ0.19 (Pr i ) and Ϫ0.3 (Bu t ).…”

Section: Alkyl Substituent Effectsupporting

confidence: 87%

Photochemical generation and lifetimes in water of p-aryloxy- and p-alkoxyphenylnitrenium ions

Ramlall¹,

McClelland²

1999

J. Chem. Soc., Perkin Trans. 2

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Section: Alkyl Substituent Effectsupporting

confidence: 87%

Photochemical generation and lifetimes in water of p-aryloxy- and p-alkoxyphenylnitrenium ions

Ramlall¹,

McClelland²

1999

J. Chem. Soc., Perkin Trans. 2

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“…Therefore, the reaction of the iminium cation with the weaker nucleophile but also less powerful leaving group OH Ϫ was also studied (in MeOH). The rate constant found for this reaction is a reasonable 21 8.8 × 10 8  Ϫ1 s Ϫ1 . If methanol is added to solutions of 3 or 4 in acetonitrile, it turns out that the k(decay of ylide) vs. [MeOH] plot (not shown) is 'curved up', i.e., the reactivity increases with increasing methanol concentration.…”

Section: Aziridines 3-5mentioning

confidence: 59%

Laser flash photolysis of aziridines. Spectroscopic and kinetic characterization of azomethine ylides. Their [3 + 2] cyclization with alkenes and protonation by water–alcohols to yield iminium ions 1

Gaebert¹,

Siegner²,

Mattay³

et al. 1998

J. Chem. Soc., Perkin Trans. 2

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“…The corresponding observed diastereoselectivities, as well as the steric parameters of the nucleophile alkyl MgCl, are reported in Table 2 as well as in Fig 3. The Taft steric parameter À E s was earlier obtained from kinetic data, by acid-and base-catalyzed hydrolysis of esters in aqueous acetone [40], and approximately follows the size of the group. It is independent from polar effects [41] but may be sensitive to solvation, field, or resonance effects [42], and its correlation with the observed diastereoselectivity for adducts 3d -8d is not perfect, as shown by Eqn. 8.…”

mentioning

confidence: 99%

Diastereoselective Alkyl Grignard 1,4‐Additions to para‐Substituted (2R)‐N‐Cinnamoylbornane‐10,2‐sultam Derivatives: Influence of N‐Atom Pyramidalization

Piątek

Sadowska

Chapuis

et al. 2011

Helvetica Chimica Acta

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Dedicated to Dr. Charles Fehr, on the occasion of his 65th birthday Several typical 13 C-NMR displacements (of C¼O, C(a), C(b), and C ipso ), as well as conformational or energy properties (SÀNÀC¼O dihedral angle, DE syn/anti; HOMO/LUMO) could be correlated with the electronic parameters of p-substituted N-cinnamoylbornane-10,2-sultams 2. Even under nonchelating conditions, the pyramidalization of the sultam N-atom decreases for electron-attracting psubstituents, inducing a modification of the sultam-ring puckering. Detailed comparison of the X-ray structure analyses of 2b, 2d, and 2m showed that the orientation of the sterically directing pseudo-axial S¼O(2) and HÀC(2) is modified and precludes any conclusion about the p-facial stereoelectronic influence of the N lone pair on the alkyl Grignard 1,4-addition. We also showed that the aggregating alkyl Grignard reagent may be used in equimolar fashion, demonstrating that the sultam moiety is chelated with a Lewis acid such as MgBr 2 . The Schlenk equilibrium may also be used to generate the appropriate conditions of effective 1,4-diastereoselectivity. Although the anti-s-cis/syn-s-cis difference of conformational energies for N-cinnamoyl derivatives 2 is higher than for the simple N-crotonoyl analogue, an Xray structure analysis of the SO 2 /C¼O syn derivative 10 confirms the predictive validity of our conformational calculations for DE 1.8 kcal/mol. 3 ) Thus, for example, the conjugate addition of an organozirconocene proceeds with only 9% d.e. on the N-crotonoylbornane-10,2-sultam [3a], while, in absence of electronic conjugation with the carbonyl group, syn-dihydroxylation involving the C(b) atom proceeds with only 0 -20% d.e., even in the cooperative presence of two conformationally rigidifying and directing prosthetic groups [4]. In this latter case, it is noteworthy that the weak purely steric influence of the sultam moiety on C(b) directs the approach on the same face as for a C(a) steric attack.Helvetica Chimica Acta -Vol. 94 (2011) 2142 4 ) Indeed, whereas chemical reactions involving either the C(a) or both C(a) and C(b) atoms are legion (> 300 reports), specific reactions at the C(b) atom are limited, e.g., to either MeNOor electrochemical CO 2 [7], or RS À [8] Michael additions, as well as the 1,4additions of simple Grignard reagents [9], Mg-cuprates [10], Li-cuprates [11], t BuHgCl-or InÀCu Igenerated alkyl radical [12], Rh I or Cu I /zirconocenes [3], EtAlCl 2 or Cu I /zincates [13], TiCl 4 / allylSiMe 3 [14], TiCl 4 /Cl 3 CLi [15], or Li-enolates [16]. Method [6] apparently does not involve any chelate and gave ca. 50% d.e. in favor of the same face as for a C(a) steric attack, anti to the N lp, in case of the more reactive SO 2 ÀC¼O syn s-cis conformer. The same p-facial selectivity was also obtained in almost all the other examples of chelation [3b] [8 -16] (see the discussion for exceptions). The absolute configuration of the 1,4-adducts was not determined in [3a] [7] [11f] [12] [13b] [14]. We are indebted to Prof. M. J. Wu for providing confir...

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Radiation chemical production, lifetimes, and structure-activity relations for .alpha.-dialkoxyalkyl carbocations in aqueous solutions: Importance of solvation for cation reactivity

Cited by 25 publications

References 3 publications

Photochemical generation and lifetimes in water of p-aryloxy- and p-alkoxyphenylnitrenium ions

Photochemical generation and lifetimes in water of p-aryloxy- and p-alkoxyphenylnitrenium ions

Laser flash photolysis of aziridines. Spectroscopic and kinetic characterization of azomethine ylides. Their [3 + 2] cyclization with alkenes and protonation by water–alcohols to yield iminium ions 1

Diastereoselective Alkyl Grignard 1,4‐Additions to para‐Substituted (2R)‐N‐Cinnamoylbornane‐10,2‐sultam Derivatives: Influence of N‐Atom Pyramidalization

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