The Spectral Properties of Alkoxymethyl Cations<sup>1</sup>

Ramsey, Brian G.; Taft, Robert W.

doi:10.1021/ja00965a030

Cited by 76 publications

(31 citation statements)

References 2 publications

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“…Although a large number of stable hydrocarbon bis-and tris-(alkoxy)methyl cations have been prepared and characterized [9][10][11], attempts to generate the corresponding polyfluorinated cations [for example, (R f O) 3 C + by treatment of (R f O) 3 CF (R f = C 2 F 5 , n-C 4 F 9 -) with SbF 5 ] [7] have been unsuccessful to date. At present, no cation containing two or more fluoroalkoxy substituents is known.…”

Section: Introductionmentioning

confidence: 99%

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Петров¹,

Marchione

Marshall

2006

Journal of Fluorine Chemistry

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Section: Introductionmentioning

confidence: 99%

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Петров¹,

Marchione

Marshall

2006

Journal of Fluorine Chemistry

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“…With the appropriate choice of conditions it is possible to generate alkoxyhydroxy substituted carbenium ions as long-lived intermediates (1,11). Despite the large number of studies describing the properties of these cations, there have been few reports of the determination of their structures using direct method^.^ The conformational preferences of some acyclic dialkoxyhydroxy carbenium ions have been determined by NMR studies (17), but, this methodology cannot be extended to the types of cyclic systems used in establishing the concept of stereoelectronic control. In this paper we describe the determination of the crystal structures of three dialkoxy carbenium ion salts derived by the alkylation of six-membered ring lac tone^.^?^ These structures firmly establish the conformation of these cations and support the assumptions that have been made by previous workers.…”

Section: Introductionmentioning

confidence: 99%

Structural studies on 6-ethoxytetrahydropyrylium cations; stereoelectronic control in the reactions of lactonium salts

Childs¹,

Kostyk²,

Lock³

et al. 1991

Can. J. Chem.

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. Can. J. Chem. 69,2024Chem. 69, (1991.The structures of 6-ethoxy-2,3,4,5-tetrahydropyrylium, 1, 6-eth0xy-2-methyl-2,3,4,5-tetrahydropyrylium, 2, and 2-ethoxy-3,4,4a,5,6,7,8,8a-octahydro-1-benzopyrylium, 3, hexachloroantimonates have been determined by X-ray crystallography. In each case the tetrahydropyrylium rings exist in shallow half-chair conformations with the cationic centers C(6), C(5), 0(1), and O(6) having a planar arrangement. The cations all have a Z conformation about the 0 ( 6 j C ( 7 ) bonds and it is shown that this conformation is also preferred in solution by comparison of narrow-line I3C NMR spectra in the solid state and solution. The O ( l W ( 2 ) and 0 ( 6 w ( 7 ) bond distances in 1-3 are significantly longer than those of comparable bonds in neutral esters. The length of the O ( l W ( 2 ) bond is very dependent on substitution at C(2) suggesting a considerable fraction of the positive charge resides on this carbon as well as C(7). The closest cationlanion interactions present in the crystal lattices of these salts are between the chlorine atoms of the anion and the cationic center, C(6). These interactions provide information on the origin of the stereoselectivity observed in nucleophilic attack on these cations. The conformations, details of the C-0 bonding, and closest contacts between cation and anion are discussed in terms of the concept of stereoelectronic control.Key words: 6-ethoxytetrahydropyrylium cations, lactonium salts, structure, X-ray, stereoelectronic control. Chem. 69, 2024Chem. 69, (1991.Les structures des hexachloroantimonates des 6-Cthoxy-2,3,4,5-tttrahydropyrylium (I), 6-tthoxy-2-mCthyl-2,3,4,5-tttrahydropyrylium (2) et 2-~thoxy-3,4,4a,5,6,7,8,8a-octahydro-l-benzopyrylium (3) ont Ct C dCterminCes par diffraction des rayons-X. Dans chaque cas, les cycles tCtrahydropyrylium existent dans des conformations demi-chaises peu profondes dans lesquelles les centres cationiques C(6), C(5), O(1) et O(6) sont dans un arrangement planaire. Les cations possbdent tous une conformation Z autour des liaisons 0 ( 6 w ( 7 ) ; par comparaison des bandes fines des spectres RMN du 13C i i 1'Ctat solide et en solution, on a aussi dtmontrC que cette conformation est aussi la conformation privilCgiCe en solution. Les longueurs des distances 0 ( 1 ) 4 ( 2 ) et O(6)-X(7) des composCs 1-3 sont beaucoup plus longues que celles des liaisons comparables des esters neutres. La longueur de la liaison O ( l W ( 2 ) dtpend beaucoup de la substitution en C(2); ce rCsultat suggkre qu'une fraction importante de la charge positive se trouve sur ce carbone ainsi que sur celui en C(7). Les interactions cation/anion le plus proches observCes dans les rCseaux cristallins de ces sels se retrouvent entre les atomes de chlore de l'anion et le centre cationique C(6). Ces interactions fournissent de l'information sur l'origine de la stCrCosClectivitC observCe lors des attaques nuclCophiles sur ces cations. On fait appel au concept de contr6le stCrCoClectronique pour discuter des conformations, des details de l...

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“…61 This consideration is supported by NMR studies 62–64 and by DFT calculations, which suggest that the E ,Z-configuration of simple dialkoxycarbenium ions is >2.5 kcal.mol −1 more stable than the E , E -configuration. Furthermore, alkylation of the carbonyl oxygen in δ-lactones gave the corresponding cyclic dialkoxycarbenium ions in the E , Z -configuration in two examples for which the structure was established crystallographically.…”

Section: Discussionmentioning

confidence: 93%

Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation

Wen

Crich

2015

J. Org. Chem.

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The preparation of a series of mannopyranosyl donors carrying 2-O-(2-oxoalkyl) ethers and their use in glycosylation reactions is described. The formation of cyclic products with the simple 2-O-phenacyl ether and with the 2-O-(t-butoxycarbonylmethyl) ether establishes the stereoelectronic feasibility of the participation in such systems. The high β-selectivities observed with the bis-trifluoromethyl phenacyl ether indicate that participation can be suppressed through the introduction of electron-withdrawing substituents. The high β-selectivities and absence of cyclic products observed with the 2-O-(methoxycarbonylmethyl) ether excludes the effective participation of esters through six-membered cyclic intermediates in this series. The results are discussed in terms of the conformation of cyclic dioxenium ions (E,E-, E,Z- or Z,Z,-) and in the context of “neighboring group” participation by non-vicinal esters in glycosylation. Methods for the deprotection of the 2-O-phenacyl and 2-O-(methoxycarbonylmethyl) ethers are described.

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The Spectral Properties of Alkoxymethyl Cations¹

Cited by 76 publications

References 2 publications

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Structural studies on 6-ethoxytetrahydropyrylium cations; stereoelectronic control in the reactions of lactonium salts

Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation

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The Spectral Properties of Alkoxymethyl Cations1

Cited by 76 publications

References 2 publications

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Structural studies on 6-ethoxytetrahydropyrylium cations; stereoelectronic control in the reactions of lactonium salts

Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation

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The Spectral Properties of Alkoxymethyl Cations¹