Cleavage of aryl carboxylates

Cleavage of aryl carboxylates (general procedure) To a solution of NaHTe (prepared from Te (1.30 g, 10 mmol) and NaBH4 (0.90 g, 24 mmol) in EtOH (20 mL)) buffered with AcOH (1.2 ml) in EtOH (5 ml.) is added the aryl carboxylate (5 mmol). The mixture is refluxed for 30 min, poured into ice-H20 (200 mL), extracted with CHCI3 and the... 

Scheme 11.10 Transition metal-catalyzed cleavage of sp3 C—O bonds, (a) Ni-catalyzed cleavage of aryl carboxylates [97] (b) FeCI3-catalyzed cleavage of benzyl ethers [98] ...

Synthesis of aryl carboxylic acids by base catalyzed cleavage of keto pyridinium salts formed by reaction of a-haloketone derivatives with pyridine (see 1st edition). 

In these compounds the following substituents can be present alkyl,alkenyl,aryl, halogen,sulfonic acid, amino, hydroxyalkyl, acyl, and carboxyl. The cleavages of 5,5 - (109) and 3,5 -diisoxazolyl (111) proceed similarly both isoxazole rings are cleaved in the former (109—> 110). ... 

CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Chrysene, 58,15, 16 fzans-Cinnamaldehyde, 57, 85 Cinnamaldehyde dimethylacetal, 57, 84 Cinnamyl alcohol, 56,105 58, 9 2-Cinnamylthio-2-thiazoline, 56, 82 Citric acid, 58,43 Citronellal, 58, 107, 112 Cleavage of methyl ethers with iodotri-methylsilane, 59, 35 Cobalt(II) acetylacetonate, 57, 13 Conjugate addition of aryl aldehydes, 59, 53 Copper (I) bromide, 58, 52, 54, 56 59,123 COPPER CATALYZED ARYLATION OF /3-DlCARBONYL COMPOUNDS, 58, 52 Copper (I) chloride, 57, 34 Copper (II) chloride, 56, 10 Copper(I) iodide, 55, 105, 123, 124 Copper(I) oxide, 59, 206 Copper(ll) oxide, 56, 10 Copper salts of carboxylic acids, 59, 127 Copper(l) thiophenoxide, 55, 123 59, 210 Copper(l) trifluoromethanesulfonate, 59, 202... 

Linkers that enable the preparation of y-lactones by cleavage of hydroxy esters from insoluble supports are discussed in Section 3.5.2. Resin-bound y-lactones have been prepared by Baeyer-Villiger oxidation of cyclobutanones [39], by intramolecular addition of alkyl radicals to oximes [48], by electrophilic addition of resin-bound sele-nenyl cyanide or bromide to 3,y-unsaturated acids (Figure 9.2 [100]), and by palladium-mediated coupling of resin-bound aryl iodides with allenyl carboxylic acids (Entry 10, Table 5.7 [101]). 

Of particular interest to combinatorial chemistry is the use of immobilised functionalised boronic acid templates which are capable of further transformations [20]. For instance, an aryl carboxylic acid 50 can be converted into the corresponding amide 51 (Scheme 12), whilst still being attached to the resin. Benzyl amine and butylamine were coupled efficiently to afford (after cleavage) the corresponding amides 52 in high yield (Scheme 12). 

Although the above reactions are common to alcohols and phenols, there are several reactions that can be done on alcohols but not phenols, and vice versa. For example, unlike alcohols, phenols cannot be converted to esters by reaction with a carboxylic acid under acid catalysis. Reactions involving the cleavage of the C-O bond are also not possible for phenols. The aryl C-O bond is stronger than the alkyl C-O bond of an alcohol. 

If care is taken to avoid ring cleavage, 5-aryl-l,3,4-oxadiazole-2-carboxylic acids will undergo typical reactions such as the formation of acid chlorides, amides and esters. Decarboxylation may occur on heating, for example with 5-amino-l,3,4-oxadiazole-2-carboxylic acids (77JHC1385), and an amide has been dehydrated to a nitrile (78GEP2808842). 

---