Carbon replacement strategies

STRATEGY (a) Look at the backbone of the polymer, the long chain to which the other groups are attached. If the atoms are all carbon atoms, then the compound is an addition polymer. If ester groups are present in the backbone, then the polymer is a polyester and the monomers will be an acid and an alcohol. If the backbone contains amide groups, then the polymer is a polyamide and the monomers will be an acid and an amine, (b) If the monomer is an alkene or alkvne, then the monomers will add to one another a Tr-bond will be replaced by new cr-bonds between the monomers. If the monomers are an add and an alcohol or amine, then a condensation polymer forms with the loss of a molecule of water. 

During the last few years, the PKR has been developed as a straightforward and practicable method for the synthesis of highly substituted cyclopentenones. But for many synthetic chemists, the employment of poisonous CO still represents a disadvantage. Hence, different strategies focused on the replacement of carbon monoxide within the reaction sequence. Recent successful examples are based on results from the early 1960s, which dealt with the transition metal catalyzed decarbonylation of organic oxo compounds [67]. 

Recent developments have impressively enlarged the scope of Pauson-Khand reactions. Besides the elaboration of strategies for the enantioselective synthesis of cyclopentenones, it is often possible to perform PKR efficiently with a catalytic amount of a late transition metal complex. In general, different transition metal sources, e.g., Co, Rh, Ir, and Ti, can be applied in these reactions. Actual achievements demonstrate the possibility of replacing external carbon monoxide by transfer carbonylations. This procedure will surely encourage synthetic chemists to use the potential of the PKR more often in organic synthesis. However, apart from academic research, industrial applications of this methodology are still awaited. 

The Kyoto protocol had identified the development of an alternative biofuel from biomass as one of several areas deserving of research support, since this type of renewable fuel could help reduce greenhouse gas emissions. The use of bioethanol as a viable motor fuel to replace or augment gasoline is an attractive component of an integrated strategy to reduce the release of detrimental hydrocarbons, carbon monoxide, nitrogen oxide, sulfur dioxide, and aromatics (2-3). 

Strategy To identify the carboxylic acid chloride used in the Friedel-Crafts acylation of benzene, break the bond between benzene and the ketone carbon and replace it with a -Cl. 

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