Current Organic Chemistry

ISSN: 1385-2728

Current Organic Chemistry
Volume 11, Number 13, September 2007

Contents


Heterogeneous Catalysis in the Meerwein-Ponndorf-Verley Reduction of Carbonyl Compounds Pp. 1113-1125
José Rafael Ruiz and César Jiménez-Sanchidrián
[Abstract]


Stepwise Two-Electron-Transfer Reduction of Cyclic Ethers and Lactones with Alkalide K^-, K⁺(15-Crown-5)₂ Pp. 1126-1134
Zbigniew Grobelny, Andrzej Stolarzewicz and Adalbert Maercker
[Abstract]


Lewis and Brønsted Acid Mediated Ring-Opening Reactions of Methylenecyclopropanes and Further Transformation of the Ring Opened Products Pp. 1135-1153
Li-Xiong Shao and Min Shi
[Abstract]


¹⁵N NMR Spectroscopy in Structural Analysis: An Update (2001 - 2005)† Pp. 1154-1205
Radek Marek, Antonín Lycka, Erkki Kolehmainen, Elina Sievänen and Jaromír Toušek
[Abstract]




Abstracts

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Heterogeneous Catalysis in the Meerwein-Ponndorf-Verley Reduction of Carbonyl Compounds
José Rafael Ruiz and César Jiménez-Sanchidrián

The Meerwein-Ponndorf-Verley (MPV) reaction involves the catalysed transfer of hydrogen from an alcohol to a carbonyl compound and provides an effective method for synthesizing carbonyl compounds under very mild conditions. The method, which requires the use of a catalyst, is high selective as it leaves most reducible functional groups in the carbonyl reactant untouched. The classical MPV reaction is conducted in a homogeneous phase, usually in the presence of a metal alkoxide as catalyst. The process has been extensively studied over the past 15 years, using heterogeneous catalysts that minimize or avoid many of the problems inherent in homogeneous catalysis. The most widely used among such catalysts consist of metal oxides (particularly aluminium, magnesium and zirconium oxides), magnesium phosphates, layered double hydroxides, mesoporous solids and zeolitic compounds. These materials vary widely in nature and include acid, basic, neutral, mesoporous and microporous solids. This allows virtually any type of carbonyl compound to be reduced by using an appropriate available catalyst. This paper reviews the most salient advances in MPV reduction processes involving heterogeneous catalysts, with emphasis of the reaction proper rather than on the nature of the catalyst. Special attention is given to the shape selectivity provided by zeolitic materials and layered double hydroxides for some carbonyl compounds.


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Stepwise Two-Electron-Transfer Reduction of Cyclic Ethers and Lactones with Alkalide K^-, K⁺(15-Crown-5)₂
Zbigniew Grobelny, Andrzej Stolarzewicz and Adalbert Maercker

The potassium anion possesses two valence electrons in its outer orbital. These two electrons might be transferred to an acceptor molecule simultaneously or stepwise. The stepwise mechanism had been stated till now experimentally only for the reaction of alkalide K^-, K⁺(18-crown-6) with phenylacetylperoxide. A concept of this review was to ascertain if that mechanism has a more general character. Reactions of potassium anions of alkalide K^-, K⁺(15-crown-5)₂ with some cyclic ethers and lactones of different ring size were selected for that purpose.


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Lewis and Brønsted Acid Mediated Ring-Opening Reactions of Methylenecyclopropanes and Further Transformation of the Ring Opened Products
Li-Xiong Shao and Min Shi

Transition metal-catalyzed reactions of methylenecyclopropanes (MCPs) 1 have been widely explored in this area of study over the past decades and some corresponding reviews have been reported. On the contrary, less attention has been paid for the Lewis acid or Brønsted acid-mediated reactions of MCPs. In the continuum of Lewis acid or Brønsted acid-mediated transformations of MCPs 1, we have found some novel transformation of MCPs 1 via another way. This review mainly puts its emphasis on the recent progress on the Lewis acid or Brønsted acid mediated ring-opening reactions of MCPs 1 developed by the group and some others’ corresponding work will also be involved.


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¹⁵N NMR Spectroscopy in Structural Analysis: An Update (2001 - 2005)†
Radek Marek, Antonín Lycka, Erkki Kolehmainen, Elina Sievänen and Jaromír Toušek

Since our previous review article (Curr. Org. Chem. 2002, 6, 35), significant improvements and an array of ¹⁵N NMR applications in structural analysis have been published. This report aims to update coverage of improvements in methodology and various types of applications published over the period 2001 - 2005.

Substantial progress in cryogenic probe technology and the commercial availability of cryoprobes have facilitated the measurement of ¹⁵N NMR parameters.

The number of solid-state applications has increased significantly during the past few years. In contrast to our previous review, this article covers ¹⁵N solid state studies. The ¹⁵N NMR chemical shifts of organic molecules are routinely measured by using cross-polarization magic-angle spinning (CP/MAS) techniques. The principal values of the chemical shift tensors can also be determined. ¹H-¹⁵N and ²H-¹⁵N distance measurements made by means of ¹H detection are currently used in NMR crystallography.

User friendly quantum chemical programs allow for the routine calculation of ¹⁵N chemical shielding and indirect spinspin coupling constants, especially using density functional theory (DFT).

Applications of ¹⁵N NMR spectroscopy in various fields of chemistry are summarized here. Major sections represent tautomerism, complexation, protonation, and hydrogen bonding. The other topics comprise N-alkylation, N-oxidation, regioisomerism, and changes in configuration or conformation.