Sulfones double metallation

Fast Color Salts. In order to simplify the work of the dyer, diazonium salts, in the form of stable dry powders, were introduced under the name of fast color salts. When dissolved in water they react like ordinary diazo compounds. These diazonium salts, derived from amines, free from solubilizing groups, are prepared by the usual method and are salted out from the solutions as the sulfates, the metallic double salts, or the aromatic sulfonates. The isolated diazonium salt is sold in admixture with anhydrous salts such as sodium sulfate or magnesium sulfate. 

Not only heteroatom-H bonds but also activated C-H bonds can add to the jr-system of an allene. Since carbon lacks a free electron pair, the transition metal catalyst must first activate the C-H bond the new species formed will then react with the C=C double bond. For efficient activation of that kind, two acceptors (typically esters, nitriles and/or sulfones) are necessary. In accord with this mechanistic picture is the fact that the reaction does not benefit from an additional base (which would deproto-nate the pronucleophile). Hence neutral conditions are even better. 

The addition reactions which were discussed in Sections 4.1 and 4.2 are initiated by interaction of a proton with the alkene, which causes nucleophilic attack on the double bond. The role of the initial electrophile can be played by metal cations as well. Mercuric ion is the reactive electrophile in several synthetically valuable procedures.12 13 The most commonly used reagent is mercuric acetate, but the trifluoroacetate, trifluoromethane-sulfonate, or nitrate salts are preferable in some applications. A general mechanism depicts a mercurinium ion as an intermediate.14 Such species can be detected by physical measurements when alkenes react with mercuric ions in nonnucleophilic solvents.15 Depending on the structure of the particular alkene, the mercurinium ion may be predominantly bridged or open. The addition is completed by attack of a nucleophile at the more substituted carbon ... 

The first step in the cycle, analogous to the cross-coupling reactions, is the oxidative addition of an aryl (vinyl) halide or sulfonate onto the low oxidation state metal, usually palladium(O). The second step is the coordination of the olefin followed by its insertion into the palladium-carbon bond (carbopalladation). In most cases palladium is preferentially attached to the sterically less hindered end of the carbon-carbon double bond. The product is released from the palladium in a / -hydrogen elimination and the active form of the catalyst is regenerated by the loss of HX in a reductive elimination step. To facilitate the process an equivalent amount of base is usually added to the reaction mixture. 

Porphyrins can also be sulfonated a t the peripheral positions, and copper(II) porphyrins react with thiocyanogen to give the methine-thiocyanatoporphyrin which can be hydrolyzed to the corresponding mercapto derivative. Reactions between metalloporphyrins and car- benes are known, but they tend to give mixtures of products owing to addition at methine positions as well as across peripheral double bonds. Nitrenes also react with metal-free porphyrins to give insertion products and methine-substituted derivatives. 

Aziridines can add to carbon—carbon multiple bonds. Elevated temperature and alkali metal catalysis are required in the case of nonpolarized double bonds (193—195). On the other hand, the addition of aziridines onto the conjugated polarized double or triple bonds of a,p-unsaturated nitriles (196—199), ketones (197,200), esters (201—205), amides (197), sulfones (206—209), or quinones (210—212) in a Michael addition-type reaction frequendy proceeds even at room temperature without a catalyst. The adducts obtained from the reaction of aziridines with a,p-unsaturated ketones, eg, 4-aziridinyl-2-butanone [503-12-8] from 3-buten-2-one, can be converted to 1,3-substituted pyrrolidines by subsequent ring opening with acyl chlorides and alkaline cyclization (213). 

The reason for the E selectivity lies in the mechanism of the elimination. The first step is believed to be two successive electron transfers from the reducing agent (sodium metal) to the sulfone. Firstly, a radical anion is formed, with one extra unpaired electron, and then a dianion, with two extra electrons and therefore a double negative charge. The dianion fragments to a transient carbanion that expels acetate or benzoate to give the double bond. 

Saturation of a carbohydrate double bond is almost always carried out by catalytic hydrogenation over a noble metal. The reaction takes place at the surface of the metal catalyst that absorbs both hydrogen and the organic molecule. The metal is often deposited onto a support, typically charcoal. Palladium is by far the most commonly used metal for catalytic hydrogenation of olefins. In special cases, more active (and more expensive) platinum and rhodium catalysts can also be used [154]. All these noble metal catalysts are deactivated by sulfur, except when sulfur is in the highest oxidation state (sulfuric and sulfonic acids/esters). The lower oxidation state sulfur compounds are almost always catalytic poisons for the metal catalyst and even minute traces may inhibit the hydrogenation very strongly [154]. Sometimes Raney nickel can... 

Immobilization of a sulfonated chiral manganese-salen catalyst on a fimctio-nalized Merrifield resin yielded a remarkably active epoxidation catalyst [42]. Its activity and enantioselectivity was examined by epoxidation of 6-cyanochromene, indene, styrene, 4-methylstyrene, and trans-stilbene using m-CPBA/NMO and quantitative yields were obtained in less than 5 min. Enantioselectivities were between 33% (4-methylstyrene) and 96% ee (6-cyanochromene). The same complex was also supported on silica and a layered double hydroxide (LDEI) and the catalytic performances of the systems were compared. Recycling experiments were carried out and the silica-based system showed metal leaching combined with a significant decrease in yield and ee. The layered double hydroxide- and resin-catalysts exhibited a slight decrease in activity and constant ee values in five consecutive reactions. 

---