Directing groups carboxyl

With commercially available boronate esters as aryl coupling partners, the first Pd(ll)-catalyzed P-C(sp )-arylation of simple carboxylic acids was reported (Scheme 1.2) [5]. The reaction presumably relied on the binding of carboxylate directing group to Pd(ll) center, triggering a C-H activation/transmetalation/ reductive elimination sequence. The P-arylated carboxylic acids can be obtained in satisfactory yields. It represents an important step forward in arylation of C(sp )-H bonds. 

To direct the synthesis so that only Phe Gly is formed the ammo group of phe nylalanme and the carboxyl group of glycine must be protected so that they cannot react under the conditions of peptide bond formation We can represent the peptide bond for matron step by the following equation where X and Y are amine and carboxyl protecting groups respectively... 

When the Woodward-Eschenmoser synthesis began, it was known from the work of Bernhauer et al.5 that cobyric acid (4), a naturally occurring substance, could be converted directly into vitamin B12. Thus, the synthetic problem was reduced to the preparation of cobyric acid, a molecule whose seventh side chain terminates in a carboxylic acid group and is different from the other side chains. Two strategically distinct and elegant syntheses of the cobyric acid molecule evolved from the combined efforts of the Woodward and Eschenmoser groups and both will be presented. Although there is naturally some overlap, the two variants differ principally in the way in which the corrin nucleus is assembled. 

One method for preparing imidazolylstannanes is direct metalation followed by treatment with RjSnCl [21]. l-Methyl-2-tributylstannylimidazole, derived in such manner, was coupled with 3-bromobenzylphosphonate (26) to furnish heterobiaryl phosphonate 27 [22], Under the same reaction conditions, 4-bromobenzylphosphonate led to the adduct in 69% yield, whereas only 24% yield was obtained for 2-bromobenzylphosphonate. The low yield encountered for the ortho derivative may be attributed to the steric factors to which the Stille reaction has been reported to be sensitive [23]. Heterobiaryl phosphonates such as 27 are not only substrates for the Wadsworth-Homer-Emmons reaction, but also bioisosteric analogs of the carboxylic acid group. 

Further studies by the same authors have demonstrated that PFj acts a hydrogen bond-acceptor template in the assembly of several other interwoven structures. In an extensive study aimed at using a combination of hydrogenbonding motifs to self-assemble pseudorotaxanes into more complex structures it was discovered that PFj assists on the organization of the components that yield the final superstructure [74]. Particularly, it was found that this anion dictates the orientation of the two carboxylic acid groups of the [3]pseudorotaxanes 58 and 59 (see Schemes 27 and 28) when these groups are co-directional with respect to each other the formation of discrete hydrogen-bonded dimers is observed. 

The aromatic acids, as you would suspect from the name, have a benzene ring connected directly to the carboxyl signature group. Dicarboxylic acids have carbo l, groups attached in two places. Monocarboxylic adds have only one, and of course, the poly acids have three or more.. ... 

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