<sup>1</sup>H‐ und <sup>13</sup>C‐NMR‐spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3‐Dioxan‐2‐ylium‐Salzen

Paulsen, Hans; Schüttpelz, Eike

doi:10.1002/mrc.1270121104

Cited by 7 publications

References 11 publications

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Synthesis and properties of 1,3-dioxanium salts (review)

Kosulina¹,

Kul'nevich²

1999

Chem Heterocycl Compd

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Syntheses, structures, spectral characteristics, and chemical properties of 1, 3-dioxanium salts are reviewed.Salts of 1,3-dioxanium and 1,3-dioxolanium are unique class of nonaromatic cyclic carbonium compounds that have a positive charge on the meso-carbon atom of the O-C § fragment. The presence of the stabilized carbocation makes acyloxonium salts as convenient models for studying the reactivity and behavior of carbenium ions. Salts of 1,3-dioxolanium have been studied more than those of 1,3-dioxanium. Until recently, this was due to their greater stability and convenient synthetic method by acylation of pinacone hydrate with acylium perchlorates [1]. Recent reports indicate that the reactivity of salts with similar structures differ depending on the presence and position of substituents in the five-or six-membered rings. Salts of 1,3-dioxanium are preferred over those of 1,3-dioxolanium. o~o o~oThe review by Pittman et al.[2] on nonaromatic 1,3-heterocarbenium ions (1,3-dioxolanium, 1,3-dioxanium, 1,3-oxathiolanium, 1,3-thiolanium, 1,3-thianium, 1,3-oxathianium, 1,3-thiazolinium, 1,3-oxazolinium) contains data on 1,3-dioxanium salts only up to 1970 inclusive. Data concerning the salts of 1,3-dioxanium and 1,3-dioxolanium have recently been significantly expanded and reviewed [1]. Therefore, the aim of the present review is to supplement, generalize and systematize existing data on syntheses, structures, spectral characteristics and properties of 1,3-dioxanium salts. Certain new data on 1,3-dioxolanium salts are included for comparison. SYNTHESIS OF 1,3-DIOXANIUM SALTS1,3-Dioxanium cations were considered to be unstable intermediates in the chemistry of oxygen-containing compounds for a long time [3][4][5][6][7][8][9].From 1,3-dioxanes. For the first time in 1958 Meerwein successfully isolated crystalline 1,3-dioxanium salts, the carbonium system of which was stabilized by an inorganic anion. Thus, he subjected the starting reactant 2-ethoxy-4-methyl-1,3-dioxane to the action of an acceptor BF3"Et20 or SbCI5 [9].

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Synthesis and properties of 1,3-dioxanium salts (review)

Kosulina¹,

Kul'nevich²

1999

Chem Heterocycl Compd

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Synthesis and conformation of 2-silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes

Kosulina¹,

Kul'nevich²,

Moskalenko³

et al. 1998

Chem Heterocycl Compd

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The 1,3-dioxanium salts are not only active reagents, but also substances for the investigation of conformational transitions of the six-membered 1,3-dioxa ring under the influence of substituents at positions 2, 4, and 6, as well as the positive charge on the meso-carbon atom of the O=C + =O portion [1][2][3][4][5][6][7]. The 1,4-twist conformation of the six-membered ring of the acyloxonium ion --the 2,4,4,6-tetramethyl-l,3-dioxanium cation --was previously established [4]. The last is a precursor of the little-studied 2,2,4,4,6-substituted 1,3-dioxanes. In the case of 2-methyl-and 2-(4-bromophenyl)-2,4,4,6-tetramethyl-1,3-dioxanes, it was shown by the methods of IH and 13C NMR that the ring of the first compound can occur both in the 1,4-twist conformation [8] and the 2,5-twist conformation [9, 10], and the second has the form of a chair with the axial disposition of the 4-bromophenyl and methyl substituents at positions 2 and 6 [9, 10], whereby the conformation of its molecule is unchanged in the solid state according to the data of X-ray diffraction analysis [11].We showed [12, 13] that the reaction of 1,3-dioxanium salts with the silicon-containing Iotsich reagents affords 2-silylethynyl-substituted 1,3-dioxanes. In the continuation of these investigations, it seemed expedient to study the reactivity of 2,4,4,6-tetramethyl-l,3-dioxanium perchlorate (I) in the conditions of the organomagnesium synthesis with the aim of synthesizing new 2,2,4,4,6-substituted 1,3-dioxanes of interest in a stereochemical regard.Reaction of the salt (I) with mono-and diethynylmagnesium bromides gave, for the first time, the 2-silylethynyl-l,3-dioxanes (Ila-c).

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How does acetylcholine lose trimethylamine? A density functional theory study of four competing mechanisms

Lioe

Barlow

O’Hair

2009

J. Am. Soc. Mass Spectrom.

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Low-energy collision-induced dissociation (CID) of acetylcholine (ACh) yields only two fragment ions: the dominant C 4 H 7 O 2 ϩ ion at m/z 87, arising from trimethylamine loss; and protonated trimethylamine at m/z 60. Since the literature is replete with conflicting mechanisms for the loss of trimethylamine from ACh, in this article density functional theory (DFT) calculations are used to assess four competing mechanisms: (1) Path A involves a neighboring group attack to form a five-membered ring product, 2-methyl-1,3-dioxolan-2-ylium cation; (2) Path B is a neighboring group attack to form a three-membered ring product, 1-methyloxiranium ion; (3) Path C involves an intramolecular elimination reaction to form C¢O protonated vinylacetate; and (4) Path D is a 1,2-hydride migration reaction forming CH 2 -protonated vinylacetate. At the MP2/6-311ϩϩG(2d,p)//B3-LYP/6-31ϩG(d,p) level of theory path A is the kinetically favored pathway, with a transition-state energy barrier of 37.7 kcal mol Ϫ1 relative to the most stable conformer of ACh. The lowest energy pathway for the formation of protonated trimethylamine was also calculated to proceed via path A, involving proton transfer within the ion-molecule complex intermediate, with the exocylic methyl group being the proton donor. To confirm the site of proton transfer, low-energy CID of acetyl-d 3 -choline (d 3 -ACh) was carried out, which revealed loss of trimethylamine and the formation of Me 3 ND ϩ . (J Am Soc Mass Spectrom 2009, 20, 238 -246)

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¹H‐ und ¹³C‐NMR‐spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3‐Dioxan‐2‐ylium‐Salzen

Cited by 7 publications

References 11 publications

Synthesis and properties of 1,3-dioxanium salts (review)

Synthesis and properties of 1,3-dioxanium salts (review)

Synthesis and conformation of 2-silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes

How does acetylcholine lose trimethylamine? A density functional theory study of four competing mechanisms

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1H‐ und 13C‐NMR‐spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3‐Dioxan‐2‐ylium‐Salzen

Cited by 7 publications

References 11 publications

Synthesis and properties of 1,3-dioxanium salts (review)

Synthesis and properties of 1,3-dioxanium salts (review)

Synthesis and conformation of 2-silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes

How does acetylcholine lose trimethylamine? A density functional theory study of four competing mechanisms

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¹H‐ und ¹³C‐NMR‐spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3‐Dioxan‐2‐ylium‐Salzen