Activated Olefins and Acetylenes

Reactions.—Nucleophilic Attack on Carbon. Activated olefins and acetylenes. The full paper describing addition of P—H bonds to vinyl isocyanides has been published. The reaction of diphenylphosphine with vinyl isocyanide in the presence of base proceeds normally, whereas the corresponding reaction with phenylphosphine gave the 1,3-azaphosphole (24). 

The reactions of primary phosphines and the corresponding alkyl phosphides with a/ff-unsaturated ketones (25) have been discussed in some detail. Tetrafluoroethylene with an excess of dimethylphosphine in the gas phase gives (26) by a reaction which is thought to be initiated by the bimolecular abstraction of a hydrogen atom from dimethylphosphine by tetrafluoro-ethylene. Tetrafluoroethylene also reacts with tetramethyldiphosphine by a radical process to give l,2-bis(dimethylphosphino)tetrafluoroethane (27).  

Tertiary phosphines have been shown to be very effective catalysts for Michael reactions. They appear to participate by nucleophilic addition to the activated olefin. The cyclic phosphine (28) has been prepared by a double Michael addition of phenylphosphine to 1-propenylcyclohexenyl ketone.  

Similarly, the dihydrophosphepin (29) can be obtained from cycloaddition of phenylphosphine and hexa-l,5-diyne.  

Triphenylphosphine has been reported to react with TCNE at room temperature to give (30). 

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In their investigation of [Fe2(CO)j(//-SH)2] as an inorganic mimic of mercaptans, RSH, Seyferth and group studied the base-induced reactions of [Fe2(CO)6(//-SH)2] (516) with activated olefins and acetylenes. Like mercaptans, 516 undergoes base-induced addition to a,/ -unsaturated sys-... 

The high acidity of superacids makes them extremely effective pro-tonating agents and catalysts. They also can activate a wide variety of extremely weakly basic compounds (nucleophiles) that previously could not be considered reactive in any practical way. Superacids such as fluoroantimonic or magic acid are capable of protonating not only TT-donor systems (aromatics, olefins, and acetylenes) but also what are called (T-donors, such as saturated hydrocarbons, including methane (CH4), the simplest parent saturated hydrocarbon. 

Mn2(CO)io is only active in the presence of acetylene derivatives, where as Re2(CO)io is active in the presence of both olefinic and acetylene derivatives. 

Tetrazolium ylides are quite reactive and are easily alkylated.168 The mesoionic tetrazolium thiolate 117 readily adds bromine to yield 174 which can then react with a number of active methylene compounds to give mesoionic compounds, e.g., 175.293,294 They also undergo 1,3-dipolar cycloaddition with olefins and acetylenes to yield bicyclic tetrazolo-thiazolines... 

The chemical consequences of these MO changes is to activate the antiaromatic diene system for reaction. This activation is especially evident in Diels-Alder cyclizations, either with itself (Eq. 32) or with a variety of olefins and acetylenes.93... 

The C-H bond activation followed by addition to a double bond leads to the formation of alkylated compounds (Equation (1)). This reaction involves aromatic, aliphatic, olefinic, and acetylenic C-H bonds. 

The [Con(bipy)2 ]2+ species has also been reported to activate hydrogen peroxide and ter -butyl hydroperoxide for the selective ketonization of methylenic carbons, the oxidation of alcohols and aldehydes, and the dioxygenation of aryl olefins and acetylenes (36). Later reports (37), however, while confirming that the cobalt complexes did indeed cata-... 

These generally bind to enzyme that produces them and destroy or inhibit it. For example, olefins and acetylenes bind to nitrogen atoms in the pyrrole part of cytochrome P-450. This may lead to the release of the Fe and destruction of the enzyme. The intermediate can be detected as bound to the enzyme protein or active site. 

An application of the Pauson-Khand reaction for the synthesis of a carbaprostacyclin analogue (Scheme 11) [44] illustrates the power of organometallic methods for the activation of olefins and acetylenes. 

The variety of olefins (and acetylenes) which undergo metathesis and the variety of active heterogeneous and homogeneous catalysts which have been used make it difficult to propose one general mechanism for this reaction. There are currently several possibilities which are being considered. These are shown in Fig. 11 (54, 55). 

Photochemical reactions have been used for the preparation of various olefin, and acetylene complexes (7). Application to the coordination of dienes as ligands has not been used extensively, so far. In this article the preparative aspects of the photochemistry of carbonyls of the group 6 and group 7 elements and some key derivatives, with the exception of technetium, with conjugated and cumulated dienes will be described. Not only carbonyl substitution reactions by the dienes, but also C—C bond formation, C—H activation, C—H cleavage, and isomerizations due to H shifts, have been observed, thereby leading to various types of complexes. 

The full report of the crystal structure of Cp3Ti has appeared.1 la Diphenylacetylene reacts with CpTi(CO)2 in the cold to give the yellow monoacetylene complex Cp2Ti(CO)PhC2Ph the acetylene is readily displaced by CO and the complex is an active catalyst for the hydrogenation of olefins and acetylenes. Under more vigorous reaction conditions the metallocycle (1) is formed.12... 

Zirconaaziridines react with unsaturated C-C bonds such as (1) olefins and acetylenes [20], and with unsaturated C-X bonds such as (2) aldehydes and imines [20], (3) heterocumulenes [21,43,49],and (4) carbonates [21,22,43,50] (Scheme 5). The products generated upon workup are a-functionalized amines. Asymmetric transformations can be carried out when a chiral zirconaaziridine or inserting reagent is used optically active allylic amines and amino acid esters have been prepared, and the details of these transformations will be discussed. 

Aromatic, olefinic, and acetylenic hydrocarbons, but especially saturated hydrocarbons belong to persistent pollutants difficult to eliminate from the troposphere. The only exceptions are some aromatic compounds that undergo direct photodegradation in result of solar irradiation. Alkanes are undoubtedly much less reactive than other organic compounds including unsaturated hydrocarbons, surely because they are more completely saturated and their activation involves cleavage of the relatively strong C—H bond (s = 415 kJ). 

Olefin and acetylene complexes are important intermediates in homogeneous catalysis since complexing to a transition metal apparently activates the olefin or acetylene for further reaction. Thus free olefins... 

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

Brine shrimp toxicity guided fractionation of the extracts from two mixed Fijian collections of the cyanobacteria Lyngbya majuscula and Schizothrix sp. led to the isolation of eleven novel chlorinated lipids, taveuniamides A-K 369-379. All of these metabolites showed an intriguing constellation of unsaturation (olefinic and acetylenic bonds) and chlorination at the two termini of a 15-carbon chain. The central carbon atom of the chain (C-8) was substituted in each case with an N-acetate function. Taveuniamides F 374, G 375 and K 379 were the most potent brine shrimp toxins with LD50S between 1.7 - 1.9 mg mL , while taveuniamides A-E 373-377 showed moderate activity LD50 3-5 mg mL. Taveuniamides G 375, 1 377, and J 378 were essentially inactive at a concentration of 10 mg mL. ... 

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