Transition-metal-catalyzed addition of heteroatom-hydrogen bonds to alkynes.

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C–C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of...

Advances in Synthetic Applications of Hypervalent Iodine Compounds

Lewis Acids: From Conventional Homogeneous to Green Homogeneous and Heterogeneous Catalysis

Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

A new criterion for the determination of molecular structures from ground state rotational constants

Additions of Organometallic Reagents to C=N Bonds: Reactivity and Selectivity

The chemistry of thioketens

Bei −78°C reagieren die Dialkylthioketene 1a–d mit Phenyl- und Methyllithium unter thiophiler Addition zu den Thioathern 3a–d und 4. Die carbenoide Zwischenstufe konnte fur 2c mit Kohlendioxid und mit Methyljodid zu 7 und 8 abgefangen werden. Bei Raumtemperatur gehen die Carbenoide 2b–d α-Eliminierung zu den Alkylidencarbenen 15b–d ein, die zu den Butatrienen 13b–d, den Alkenen 14b–d und fur 15d zum CH-Insertionsprodukt 16 weiterreagieren.



Thiophilic Addition of Phenyllithium to Thioketenes



At −78°C the dialkylthioketenes 1a–d react with phenyl-and methyllithium in thiophilic additions to give the thioethers 3a–d and 4. The carbenoid intermediate 2c could be trapped with carbon dioxide or methyl iodide to 7 and 8. At room temperature α-elimination occurs in the carbenoids 2b–d with formation of the alkylidencarbenes 15b–d, which react further to yield the butatrienes 13b–d, the alkenes 14b–d, and in the case of 15d to give the CH-insertion product 16.

Thiophile Addition von Phenyllithium an Thioketene

Four-membered rings can be cleaved thermally, Photochemically, or catalytically into two π bonded fragments. Theoretical calculations, kinetic studies, and investigations of stereo- and regioselectivity have been undertaken to clarify the question of whether the reaction involves one or two steps and to permit predictions on its course. [2 + 2]-Cycloreversions have been used to clarify the structure of four-membered rings, to prepare highly reactive π electron-systems and–in combination with a [2 + 2]-cycloaddition–to protect double bonds. The combination of a cycloaddition and-reversion can be used to convert a carbonyl group into an olefin. Starting with compounds containing annelated four-membered rings, compounds with two functional groups or large ring systems can be prepared. [2 + 2]-Cycloreversions have also been discussed in connection with storage of solar energy.

[2 + 2]‐Cycloreversions

A survey of the structure and synthetic applications of organosulfur compounds is given. The emphasis is on the key features of organosulfur chemistry.

Ernst Schaumann

Papers

The chemistry of thioketens

Thiophile Addition von Phenyllithium an Thioketene

[2 + 2]‐Cycloreversions

Sulfur is More Than the Fat Brother of Oxygen. An Overview of Organosulfur Chemistry

The Chemistry of Thiohydroxamic Acids