Carbonic attack

Fluoride ion attacks the sulfur atom in 2,3-diphenylthiirene 1,1-dioxide to give ck-1,2-diphenylethylenesulfonyl fluoride (23%) and diphenylacetylene (35%). Bromide or iodide ion does not react (80JOC2604). Treatment of S-alkylthiirenium salts with chloride ion gives products of carbon attack, but the possibility of sulfur attack followed by addition of the sulfenyl chloride so produced to the alkyne has not been excluded (79MI50600). In fact the methanesulfenyl chloride formed from l-methyl-2,3-di- -butylthiirenium tetrafluoroborate has been trapped by reaction with 2-butyne. A sulfurane intermediate may be indicated by NMR experiments in liquid sulfur dioxide. 

Other examples that involve intermediate allyl cations are illustrated in Scheme 1.4. The cationic palladium(II) complex [Pd(dppp)(PhCN)2](BF4)2 coordinates the carbonyl oxygen of benzaldehyde and the activated carbonyl carbon attacks the isoprene, forming the allyl cation 10 which then cyclizes to give the 4-methyl-6-phenyl-5,6-dihydro-2H-pyran [22]. 2-Oxopropyl acrylate 11, in the presence of trimethylsilyltrifluoromethane sulfonate (TMSOTf) and methoxytrimethylsilane (MeOSMT), generates the cation 11a which is an efficient dienophile that reacts easily with the cyclohexadiene to give the Diels-Alder adduct in good yield [23]. 

These results show for the first time, the reactivity of the double bond C = N with the 2 diazopropane that constitutes an efficient route for the preparation of new heterocyclic systems. In all cases, the reaction is peris-elective only the double bond C = N is affected diazo carbon attacks the quaternary carbon of the imidate 60 and not the double bond C = O (substrates 60b and 60c). Indeed, diazopropane reacts with ketones with inverse regioselectivity (with regards to imidates 60) to yield oxadiazoUnes [32,33] (Scheme 14). 

Pyral A process for destroying toxic waste oiganochlorine compounds. The wastes are mixed with carbon and sodium carbonate and injected into a graphite-lined arc furnace. Metallic sodium, formed by reduction of the sodium carbonate by the carbon, attacks the chlorinated organic compounds, forming sodium chloride. Developed by Hydro-Quebec in the late 1980s but not yet commercialized. 

As shown in Figure 6.2c, a C substituent, which has evenly spaced n and n orbitals, raises the energy of the HOMO and lowers the LUMO, thus rendering the olefin more reactive as both a Lewis base and a Lewis acid. The electrons of the HOMO and LUMO are also delocalized onto C. The probability of attack by an electrophile or nucleophile will be governed by the magnitude of the coefficient at the particular atomic position. Polarization of both the HOMO and LUMO away from the point of attachment of the C substituent directs attack to that carbon. Attack may also be directed to C ... 

Mixtures of isomeric allylic chlorides are formed when 1,1-disubstituted allenes react with HC1.1,3-Disubstituted allenes yield products of both central and terminal carbon attacks. In contrast, selective transformations occur with HBr. The gas-phase, photocatalytic addition of HBr gives selectively vinylic bromides129 [Eq. (6.20)], while hydrobromination in solution phase yields allylic bromides130 [Eq. (6.21)] ... 

Ligand exchange on iodine(III) with carbon nucleophiles provides a useful method for synthesis of A3-iodanes with two carbon ligands. Koser and coworkers found that exposure of aryltrimethylsilanes to [hydroxyltosyloxy)-iodo]benzene 17 in refluxing acetonitrile allows the directed synthesis of diaryl-A3-iodanes [31]. The reaction involves silicon-directed ipso carbon attack on the positively charged iodine and, therefore, is regiospecific. 

Orientation of halohydrin formation The more substituted carbon of the chloronium ion bears more positive charge than the less substituted carbon. Attack by water occurs on the more substituted carbon to give the Markovnikov product. 

Cel6A (CBH II) -20% of total secreted protein Various isoenzymes (pi 5.1-6.3 pi 5.9+) (difficult to purify) 53kDa+ pi 5.9+ CBD (N-terminal) From non-reducing end Single displacement— Inversion of the anomeric carbon Attacks amorphous and crystalline cellulose Active on P-glucan... 

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