Olefins monosubstituted compounds

The chemical shift changes brought about by substituents bonded to the various positions of the cyclic alkenes are often dramatic, particularly on the position-2 olefinic hydrogen. A series of monosubstituted compounds is listed below. 

Obolentsev (268) found that olefins when passed over chromia at 480° gave more aromatics and more coke than paraffins of similar carbon number, i.e., C7 and C8 compounds. The ratio of disubstituted to monosubstituted aromatics formed from decane over chromia at 450-500°C. was from 1.2 1 to 1.4 1 according to Rozenberg (345) olefins amounted to 10 to 17 %. All theoretically possible schemes of cyclization were thought to take place. 

This collection begins with a series of three procedures illustrating important new methods for preparation of enantiomerically pure substances via asymmetric catalysis. The preparation of 3-[(1S)-1,2-DIHYDROXYETHYL]-1,5-DIHYDRO-3H-2.4-BENZODIOXEPINE describes, in detail, the use of dihydroquinidine 9-0-(9 -phenanthryl) ether as a chiral ligand in the asymmetric dihydroxylation reaction which is broadly applicable for the preparation of chiral dlols from monosubstituted olefins. The product, an acetal of (S)-glyceralcfehyde, is itself a potentially valuable synthetic intermediate. The assembly of a chiral rhodium catalyst from methyl 2-pyrrolidone 5(R)-carboxylate and its use in the intramolecular asymmetric cyclopropanation of an allyl diazoacetate is illustrated in the preparation of (1R.5S)-()-6,6-DIMETHYL-3-OXABICYCLO[3.1. OJHEXAN-2-ONE. Another important general method for asymmetric synthesis involves the desymmetrization of bifunctional meso compounds as is described for the enantioselective enzymatic hydrolysis of cis-3,5-diacetoxycyclopentene to (1R,4S)-(+)-4-HYDROXY-2-CYCLOPENTENYL ACETATE. This intermediate is especially valuable as a precursor of both antipodes (4R) (+)- and (4S)-(-)-tert-BUTYLDIMETHYLSILOXY-2-CYCLOPENTEN-1-ONE, important intermediates in the synthesis of enantiomerically pure prostanoid derivatives and other classes of natural substances, whose preparation is detailed in accompanying procedures. 

Dihydro-2-isopropyl-3.6-dimethoxypyrazine, a bis(lactim)ether, is converted into the 5-di-azo compound 1 by lithiation and diazo group transfer. The intermediate diazo compound reacts at room temperature with olefins such as cyclohexene to produce the cyclopropane derivatives with excellent diastereoselectivity . The derivative from cyclohexene is hydrolyzed by acid treatment to give methyl 7-cv(cfo-aminobicyclo[4.1.0]hcptane-7-carboxylate. The bis(lac-tim)ether diazo compound 1 is also involved in an exceptional asymmetric [2 + 1J cycloaddition producing cnantiomerically pure cyclopropenc derivatives4. Thus, reactions of the diazo compound with monosubstituted alkynes afford the spiro compounds as one diastereomer. Hydrolytic removal of the auxiliary and protection of the amino group provides enantiomerically pure methyl l-amino-2-arylcyclopropene-l-carboxylates in moderate overall yield. 

Selective hydrogenation is apparently best realized for dialkyl-la,b,2°3,298 and diaryl-acetylenes,286 and for compounds in which the triple bond is endocyclic,299 since in such cases further hydrogenation of the resulting olefins is markedly slower for instance, cyclodecene is obtained in 96% yield from cyclodecyne.296 The ethylene derivatives formed from monosubstituted... 

Agents that are oxidatively activated and inactivate the enzyme by covalently binding to it include (a) diverse sulfur compounds (e.g., carbon disulfide , parathion -, diethyldithiocarbamate , isothiocyanates , thioureas , thiophenes , tie-nilic acid - - , and mercaptosteroids , (b) halo-genated structures such as chloramphenicoF- , A-monosubstituted dichloroacetamides , and N-(2-p-nitrophenethyl)dichloroacetamide , (c) alkyl and aryl olefins and acetylenes such as... 

The regiochemical and stereochemical courses of the photocycloaddition of A-acylindoles with monosubstituted olefins such as methyl acrylate and vinyl acetate, as well as the possible mechanistic pathways for these reactions, have been the subject of several reports. In one of the earliest examples, the photocycloaddition of 1 -benzoylindole (8) and methyl acrylate (9) produced the compound 10, which was then converted via a short synthetic sequence to a variety of 2a,7b-dihydrocyclobut[h]indole derivatives 11 (Scheme 2). These compounds were in turn converted to the corresponding l//-l-benzazepines 12, through silver ion-catalyzed thermolysis reactions at 100-160°C [14, 15]. 

Aromatic compounds like benzene undergo a highly characteristic reaction called electrophilic substitution. For example, halogens, such as chlorine and bromine, instead of simply adding to the formal double bonds as if it were an olefin (i.e. electrophilic addition in which both halogen atoms add to the double bond), displace one of the hydrogen atoms to give a monosubstituted aryl halide... 

When reacting alkenes with triethylsilane it is necessary to keep in mind that the PdCl2/Et3SiH combination also promotes the double bond isomerization of monosubstituted aliphatic olefins and a-alkylidene cyclic carbonyl compounds are isomerized to a,/3-unsaturated cyclic carbonyls with tris(triphenylphosphine) rhodium chloride. ... 

Kinetic studies have been made on the thermal decomposition of a poly(oxypropylene)triol-toluene di-isocyanate copolymer foam. Following a diffusion rate-controlled step, the cellular structure collapses to a viscous liquid and degradation then occurs on a random scission basis. Products of degradation of A-monosubstituted and A A-disubstituted polyurethanes have been analysed by direct pyrolysis in the ion source of a mass spectrometer. The mono-substituted polymers depolymerize quantitatively to di-isocyanates and diols, whereas the disubstituted materials decompose selectively to secondary amines, olefins, and carbon dioxide. The behaviour of the monosubstituted polymers has been confirmed in an i.r. study of the degradation of model compounds. A study of the thermal degradation in vacuum of polyurethanes prepared from butanediol, methylene bis(4-phenylisocyanate), and hexanedioic acid-ethylene glycol-propylene glycol polyesters has been reported and reaction mechanisms proposed. ... 

Methylenecyclobatanes.—Methylenecyclobutanes and related compounds are most commonly prepared by the [2 + 2] addition of an allene to an appropriate reaction partner. The addition of allenes to some simple alkylated olefins to give alkylated methylenecyclobutanes is feasible in the presence of Lewis catalysts. The most efficient catalyst found was ethylaluminium dichloride. The reactivity of the olefins increases with increasing alkyl substitution. -Cyclohexene and monosubstituted olefins did not react under the conditions described. 

Class 3 eonsists of trimethylvinylsilane, aU tested dimethyl-substituted and most monosubstituted vinylsilanes. These compounds do not react with olefins by cross-metathesis in the presence of I, n, or HI but rather by decomposition [22]. 

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