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

Easily available glyceric aldehyde dithioacetals, (R)-1 and (R)-2, are converted via their tosylates, (R)-7a and b, and γ-elimination into nonracemic oxy-substituted cyclopropanone S,S-acetals, (R)-12 and (R)-13, in the presence of suitable electrophiles for trapping of alkoxide intermediates. Treatment of cyclopropanol (R)-14 with Burgess' reagent causes no 1,2-elimination, but a remarkable SN etherification with retention of configuration.

Facile Preparation of Novel Nonracemic Oxy‐Substituted Cyclopropanone S,S‐Acetals by γ‐Cyclisation of Glyceric Aldehyde Dithioacetal Derivatives and Studies of their Reactivity

Addition of m-chloroperbenzoic acid (6) to the thiane-derived thioketene (1) or the thioketone (8) leads to selective oxidation of their respective sulphide groups

Intramolecular competition experiments on sulphide vs. thiocarbonyl oxidation. Evidence for electronic and steric deactivation of thiocarbonyl groups

Alkynyl silyl sulfides 2 reacted with ynamines 3 to give 1:1 adducts. The structure of 4-silylcyclobut-2-enethiones 4 was confirmed by X-ray analysis of 4a. A cyclobutadiene intermediate is probably not involved in this reaction; we think that it is initiated by a silyl transfer from 2 to 3, and that this is followed by a combination of the resulting ions to give the unsaturated thioketene 7, which undergoes an electrocyclization to give products 4. In the reaction of thiones 4 with trimethyloxonium tetrafluoroborate (Meerwein salt) selective methylation at sulfur was observed to give cyclobutenethionium ions 16. Ions 16 underwent fluoride-induced desilylation with various fluoride sources to give cyclobutadienes 17, which could not be isolated, but trapping of 17 a-c was possible with dimethyl acetylenedicarboxylate yielding regioisomeric benzene derivatives 20–23. Similarly, 17 a and bis(methylthio)methylene malononitrile (24) led to hexatriene derivative 27 by a sequence of cycloaddition and two ring-opening reactions. In contrast, silyl-substituted cyclobutadienes 17d,e dimerized even in the presence of trapping agents to anti-tricyclo-[4.2.0.02,5]octadienes 29; this suggests that a two-step cycloaddition is taking place, rather than a concerted Diels-Alder reaction. Attempts to intercept 17d, e, generated from 16d,e with cyclopentadiene (30), gave deprotonation of 30 leading to substitution of the methylthio group in 16 and finally to formation of cyclobutenes 33 through a hydrogen shift.

Ernst Schaumann

Papers

Facile Preparation of Novel Nonracemic Oxy‐Substituted Cyclopropanone S,S‐Acetals by γ‐Cyclisation of Glyceric Aldehyde Dithioacetal Derivatives and Studies of their Reactivity

Intramolecular competition experiments on sulphide vs. thiocarbonyl oxidation. Evidence for electronic and steric deactivation of thiocarbonyl groups

Synthesis of 4‐Silylcyclobut‐2‐enethiones and their Use in Cyclobutadiene Generation

X‐Ray Structure Analysis of a Dialkylthioketene

Synthesis and Wittig-Horner Reactions of 1-(Functionally)Substituted 2,2-Dimethylpropanephosphonic Esters (1-t-Butyl-substituted Phosphonic Esters)