Best Synthetic Methods Functional Group Transformation

Best Synthetic Methods Functional Group Transformations 

An advantage of polymer-based reagents is that both the excess and the spent reagent are easily separated from the product. Bruno Linclau of the University of Southampton has reported J. Org. Chem. 2004, 69, 5897) the preparation of a polymer-bound carbodiimide. Exposure of the polymer to alcohol gives a family of O-alkylisoureas that smoothly convert carboxylic acids to the coiresponding esters. Methyl, benzyl, allyl and p-nitrobenzyl transfer smoothly. The polymeric r-butyl reagent could not be prepared. 

Many procedures have been developed for the conversion of an alcohol to the iodide. Nevertheless, the ZrCU-based procedure reported (Tetrahedron Lett. 2004,45, 7451) by Habib Firouzabadi and Nasser Iranpoor of Shiraz University, Iran is promising. It works well with primary, secondary and tertiary alcohols under mild conditions, and there are no organic sideproducts. 

The conversion of an alcohol to the amine is often a multi-step procedure. Jonathan M.J. William,s of the University of Bath has described (Chem. Commun. 2004, 1072) a direct Ir-catalyzed procedure for this transformation. The reaction probably involves oxidation of the alcohol to the aldehyde, imine formation, and then reduction of the imine to the amine. No secondary examples were reported. 

Oxidative decarboxylation of acids to alkenes is often accompanied by alkene rearrangement. Lukas J. Goossen of the Max-Planck-lnstitut, Muhlheim, has found (Chem. Commun. 2004, 724) that in situ activation of the acid with phthalic anhydride and inclusion of the bis phosphine DPE-Phos substantially slow alkene isomerization, which can be essentially eliminated by running the reaction to only 80% conversion. Both linear and branched carboxylic acids work well. 

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Best Synthetic Methods Functional Group Transformations... 

Aldol reactions provide a valuable synthetic method for forming carbon-carbon bonds. They can be adapted to extend the length of a carbon chain, to form cyclic compounds, and to provide intermediates that can be transformed into more useful materials. An important feature of these intermediates is that functional groups useful for later reactions are located close to or on the carbons of the newly formed C-C bond. There is an almost bewildering number of variations on the aldol reaction and we shall not mention all of them. The main thing to recognize in all of these reactions is that the acceptor molecule always is a carbonyl compound, best an aldehyde, sometimes a ketone, even an ester (see Section 18-8E). The donor molecule is some type of carbanion usually, but not always, an enolate anion. However, any substance that has a... 

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