Additions acetylenes

Asymmetric acetylene addition should be pursued to avoid the tedious final enantiomer separation by silica gel column after derivatization with an excess of expensive camphanyl chloride. 

Scheme 1.5 Acetylene addition, chiral resolution with (+)-CSA.

Once the initial benzene ring has cyclized, it can undergo sequences of H-atom abstraction followed by acetylene addition, to yield PAHs. This is known as the H-abstraction-C2H2-addition (HACA) process, proposed by Frenklach and Wang. As an aromatic species aggregates to a size over 500 amu, it adopts a particulate form and can coalesce with other PAHs to further increase in size. When many of these particles agglomerate, they form soot. Efforts to minimize soot production are widespread. Notably, decreasing the carbon content relative to oxidizer concentration in a fuel/oxidizer mixture decreases the amount of soot formed. 

Difluoroamino radical acetylene addition reactions, 33 185-189 addition reactions, 33 183-189 hydrogen abstraction reactions, 33 182-183 reactions with olefins, 33 183-185 reactions with other radicals, 33 181... 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

Some aspects of the reactivity of the A-frames formed by Reaction 1 have been explored. Carbon monoxide and sulfur dioxide are readily lost from the respective adducts upon mild heating or exposure to vacuum. The insertions of isocyanides or sulfur have not been reversed. However the oxidation of Pd2(dpm)2(/Lt-S)Cl2 to Pd2(dpm)2-(/x-S02)Cl2 can be effected by using m-chloroperbenzoic acid as oxidant. Acetylene addition is photoreversible photolysis of Pd2(dpm)2-(/Lt-C2 C02CH3 2)C12 forms dimethylacetylene dicarboxylate and Pd2(dpm)2Cl2 (14). Pd2(dpm)2X2 is a catalyst for converting dimethyl-acetylene dicarboxylate into hexamethyl mellitate, and Pd2(dpm)2-(/it-C2 C02CH3 2)X2, which forms during the reaction, is presumed to be an intermediate. 

Generally, insertion of the alkyne into a metal-P bond is observed (Scheme 10).188,190 When aminoalkynes are used, the formation of a C=N double bond inhibits the interaction of that carbon with the metal centers of the cluster.186 187 When two PR groups are present, the alkyne has been observed to bridge between them as seen in Scheme 10.195,285 A second equivalent of diphenylacetylene can substitute for two carbonyl groups on the iron triangle.195 The hetero-main group element species Fe3(CO)9(NPh) (P Bu) and Fe3(CO)9(NPh)2 have been reacted with diphenylacetylene.273 Some of the products involved in the acetylene addition reaction are shown here (241-243). 

Olefinic acetals, preparation, 263 preparations listed in table 23, 268 a, S-01efinic acetals, preparation, 37 Olefinic acetylenes, addition of alcohols, 233, 266 alkylation, SO partial reduction, 46 preparatioh, 34, 39, 46, 48, 80 preparations listed in table 6, 84 Olefinic acids, addition, of halogen, 107... 

Acetylene additions Aluminum chloride. Dimethylsilylazine. Simmons-Smith reagent Thiolacetic acid. Zinc iodide (catalyst). 

Perhaps the most useful of these 4,5-dihydro-I/7-pyrazole based routes, however, are those where the intermediate is simply oxidized with manganese(IV) oxide. As in the synthesis of 3,3-dimethyl-l-nitro-2-phenylcyclopropene (5), this sometimes makes possible the synthesis of precursors not available by the diazoalkane to acetylene addition route. In other cases, man-ganese(IV) oxide oxidation gives yields which are at least as good and often better than the diazoalkane to acetylene addition route and this method has been applied to the synthesis of nitro-, cyano-, carboxymethyl-, phenyl-, and alkyl-substituted systems. ... 

The first step in the soot formation mechanism is the formation of the first aromatic ring when aromatic species are not directly present in the feed. Thus, the formation mechanisms of benzene and the first aromatic species in hydrocarbon pyrolysis, particularly at high temperatures, have been investigated in great depth. Nevertheless, several uncertainties about these formation paths remain. Due to the high temperatures, acetylene addition reactions on unsaturated radicals play a key role (Frenklach and Wang, 1994) ... 

Acetylene additions Hexafluoro-2-butyne. Iodine azide. 1-Iodoheptafluoropropane. Acetylenic coupling n-Butyllithium. Cuprous chloride. 

Let us first compare the reactivity of pyrrole derivatives with cyclopentadiene, on the basis of FMO energy gap, with acetylene as a dienophile (Table 14). According to the FMO energy gap between reactants, the acetylene addition to the... 

Figure 3. Some typical examples of transition state structures for acetylene addition to pyrrole and its derivatives.

All this information about the reactivity of pyrrole and its derivatives as dienes for Diels-Alder reactions was obtained from the values computed on two separated reactants. It is much more appropriate to compare changes of the FMO energies for reactants to reach transition state structures. Some representative transition state structures for acetylene addition to pyrrole derivatives are presented in Figure 3. The transition state structures are for synchronous formation of both CC bonds with slightly asymmetric transition state structures, although both diene and dienophiles have a plane of symmetry that coincides with a plane of symmetry for the transition state structure. All of these transition state structures have similar bond distances for CC bonds, which is true for almost all Diels-Alder reactions. The FMO orbital changes for transformation of reactants into transition state structures are presented in Table 16. 

HOMO 1,2-dimethoxyacetylene comparable to the FMO changes for acetylene addition to pyrrole. As stated previously, the addition of acetylene to the pyrrolium ion should be examined separately because of its charge the full localization of double bonds on the pyrrole ring (an ideal diene for a Diels-Alder reaction), and the charge in the pyrrolium cation result in an exceptionally low LUMO energy. 

Table 17. Activation barriers (kcal/mol) for acetylene addition to pyrrole derivatives computed by AMI and B3LYP/6-3lG(d)//AMl computational...

The AMI optimized structures of all transition state structures from Scheme 2 are presented in Figure 4. The transition state structures presented in Scheme 1 are ones that could be expected on the basis of a general knowledge of chemical transformations. Estimated activation barriers were substantially lower (Table 18) than those generated for acetylene addition to pyrrole derivatives,... 

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