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

Aus Isothiocyanaten 1 und Keten-acetalen 2 entstehen Cycloaddukte, die ausgehend von den Sulfonylisothiocyanaten 1a–d als 2-Iminothietane 5, ausgehend von Arylisothiocyanaten 1e–h als 2-Azetidinthione 6 zu formulieren sind. In Folge- und Nebenreaktionen findet Umlagerung zu Malonsaure-Derivaten 4 und zu Thioacrylamiden 7 statt; auserdem entstehen 3-Imino-3H-1,2-dithiole 10. Umsetzungen von 2b,c mit uberschussigem Phenylisothiocyanat (1e) in der Warme ergeben 2-Thiouracile 12, 15 und 16. Die Konstitutionen von 10b und 12a konnten durch Rontgenstrukturanalysen bewiesen werden.



Cycloaddition Reactions of Heterocumulenes, XXV. Cycloadducts and Rearrangement Products from the Reaction of Isothiocyanates with Ketene Acetals



Isothiocyanates 1 and ketene acetals 2 yield cycloadducts, which starting from sulfonylisothiocyanates 1a–d have to be formulated as 2-iminothietanes 5, starting from arylisothiocyanates 1e–h as 2-azetidinethiones 6. In subsequent or side reactions, rearrangements lead to malonic acid derivatives 4 and thioacrylamides 7; furthermore, 3-imino-3H-1,2-dithiols 10 are generated. Reactions of 2b,c with excess phenylisothiocyanate (1e) on heating afford 2-thiouracils 12, 15, and 16. The constitutions of 10b and 12a could be proven by X-ray structural analyses.

Cycloadditionsreaktionen von Heterocumulenen, XXV. Cycloaddukte und Umlagerungsprodukte aus der Umsetzung von Isothiocyanaten mit Keten‐acetalen

A Silicon‐Mediated Synthesis of 3‐Deoxy‐D‐manno‐octulosonic Acid (KDO)

Cycloadditionsreaktionen von Heterokumulenen, XVIII Umsetzung des tert‐Butylcyanketens mit cyclischen Thioimidsäureestern

Die reaktiven (ar)aliphatischen Thioketone 3a–c lassen sich durch Cycloreversion der Anionen 2 von 1,3-Dithiolan-4,5-dicarbonsaureestern 1 freisetzen und mit Mesitonitriloxid (5) in eine-1,3-dipolaren Cycloadditon zu 7 abfangen Aus der Fragmentierung der Anionen 12 von 1,3-Dithiolan-1,1-dioxiden 11 lassen sich Thiobenzophenon (3d) und Thiocampher (3e) isolieren, wahrend die Thioketone 3a, c mit α-Wasserstoff in situ zu Enthiolaten 13 deprotoniert werden Die Anionen 13 reagieren mit dem Nitriloxid 5 unter Additon zu Thiohydroximsaureestern 8



Thioketones and Enethiolates by 1,3-Anionic Cycloreversion of Dithiolane Derivatives



The reactive (ar)aliphatic thioketones 3a–c are generated by cycloreversion of the anions 2 of 1,3-dithiolane-4,5-dicarboxylates 1 and are trapped by mesitonitrile oxide (5) in a 1,3-dipolar cycloaddition to give 7 From the fragmentation of anions 12 of 1,3-dithiolane 1,1-dioxides 11, thiobenzophenone (3d) and thiocamphor (3e) are isolated, whereas thioketones 3a, c with α-hydrogen are deprotonated in situ to provide enethiolates 13 Anions 13 add nitrile oxide 5 to yield thiohydroximates 8

Thioketone und Enthiolate durch 1,3‐anionische Cycloreversion von Dithiolan‐Derivaten

Durch Sattigung der 14N-Resonanz lasst sich in den H-NMR-Spektren der primaren Amide (1a bis 1d) und der Thioamide (2a bis 2g) die behinderte Rotation um die CN-Bindung des (Thio)Amid-Systems nachweisen. Mit Hilfe von Kopplungskonstanten und der Benzolverdunnungsmethode gelingt es, die Signale der Amino-Gruppe dem cis- und dem trans-NH-Proton zuzuordnen. Aus der Koaleszenz wird die freie Aktivierungsenthalpie der behinderten Rotation ermittelt und ihre Abhangigkeit von sterischen und elektronischen Effekten sowie vom Losungsmittel diskutiert.



By saturation of the 14N resonance, hindered internal rotation around the CN bond of the (thio)amide system is detected in the H-NMR spectra of the primary amides (1a to 1d) and the thioamides (2a to 2g). With the aid of coupling constants and benzene dilution shifts, it is possible to assign the signals of the amino group to the cis and the trans NH protons. From coalescence results free enthalpies of activation of hindered internal rotation are obtained, and their dependence on steric and electronic effects as well as the influence of the solvent are discussed.

Über die Struktur der Thioamide und ihrer Derivate—XXIII: 14N‐Entkoppelte H‐NMR‐Spektren und Messung der Rotationsbarrieren bei primären Amiden und Thioamiden

Ernst Schaumann

Papers

Cycloadditionsreaktionen von Heterocumulenen, XXV. Cycloaddukte und Umlagerungsprodukte aus der Umsetzung von Isothiocyanaten mit Keten‐acetalen

A Silicon‐Mediated Synthesis of 3‐Deoxy‐D‐manno‐octulosonic Acid (KDO)

Cycloadditionsreaktionen von Heterokumulenen, XVIII Umsetzung des tert‐Butylcyanketens mit cyclischen Thioimidsäureestern

Thioketone und Enthiolate durch 1,3‐anionische Cycloreversion von Dithiolan‐Derivaten

Über die Struktur der Thioamide und ihrer Derivate—XXIII: 14N‐Entkoppelte H‐NMR‐Spektren und Messung der Rotationsbarrieren bei primären Amiden und Thioamiden