Aryl chloroformates phenols

Phenols. Phenols are unreactive toward chloroformates at room temperature and at elevated temperatures the yields of carbonates are relatively poor (< 10%) in the absence of catalysis. Many catalysts have been claimed in the patent Hterature that lead to high yields of carbonates from phenol and chloroformates. The use of catalyst is even more essential in the reaction of phenols and aryl chloroformates. Among the catalysts claimed are amphoteric metals or thek haUdes (16), magnesium haUdes (17), magnesium or manganese (18), secondary or tertiary amines such as imidazole (19), pyridine, quinoline, picoline (20—22), heterocycHc basic compounds (23) and carbonamides, thiocarbonamides, phosphoroamides, and sulfonamides (24). 

Aryl ethers. Phenols are converted into methyl ethers by reaction with 1 in the presence of potassium carbonate and 18-crown-6 at 150°. The reaction involves liberation of chloroform and carbon dioxide (equation 1). If the reaction is conducted in the presence of an alkyl halide, alkyl aryl ethers are formed in generally good yield (equation 11). 

In a series of outstanding papers, Pinhey et al have shown that aryllead tricarboxylates react with soft nucleophiles to afford C-arylation products. These aryllead derivatives behave as aryl cation equivalents in reactions which involve a ligand coupling mechanism (see section 7.5).9 2 ju most cases, the reactions proceed in chloroform at 40-60 C in the presence of pyridine as a base with a ratio of substrate to organolead derivative to pyridine of 1 1 3. The substrates which easily undergo C-arylation include phenols, p-dicarbonyl compounds and their vinylogues, a-cyanoesters, a-hetero-substituted ketones, enamines and nitroalkanes. A very limited number of non-carbon nucleophiles has also been reported to react. 

Aryl chloroformates from phenols ArOH ArOCOCl... 

Phosgene reacts readily with aliphatic alcohols at room temperature or below to afford the corresponding aliphatic chloroformates in good yields, but phenols are much less reactive toward phosgene. Elevated temperatures (>100 °C) and scavengers or specifically designed catalysts (N,N -dimethylpropyleneurea, 2-undecylpyridine) are required to prepare aryl chloroformates [8, 9]. 

Triethyl orthoformate or chloroform can react with arene nucleophiles to give triphenylmethanes with three identical aryl groups.5,52,67 In addition, dialkylarylamines, when treated with dialkoxycarbenium tetrafluoro-borates under thermodynamic conditions or with triethyl orthoformate/zinc chloride in ether under anhydrous conditions, give triarylmethanes.68 For example, 4-methoxycarbazole and triethyl orthoformate in the presence of acid catalyst give 44 in 66% yield69 (Scheme 7). In general, phenolic or... 

Alcohols and phenols can be attached to support-bound alcohol linkers as carbonates [467,665,666], although few examples of this have been reported. For the preparation of carbonates, the support-bound alcohol needs to be converted into a reactive carbonic acid derivative by reaction with phosgene or a synthetic equivalent thereof, e.g. disuccinimidyl carbonate [665], carbonyl diimidazole [157], or 4-nitrophenyl chloro-formate [467] (see Section 14.7). The best results are usually obtained with support-bound chloroformates. The resulting intermediate is then treated with an alcohol and a base (DIPEA, DMAP, or DBU), which furnishes the unsymmetrical carbonate. Carbonates are generally more resistant towards nucleophilic cleavage than esters, but are less stable than carbamates. Aryl carbonates are easily cleaved by nucleophiles and are therefore of limited utility as linkers for phenols. 

The condensation of tellurium tetrachloride with aromatic compounds was one of the first methods for the preparation of aryl tellurium trichlorides. Alkyl aryl ethers react easily with tellurium tetrachloride in refluxing chloroform or carbon tetrachloride (Vol. IX, p. 1153). The trichlorotelluro group enters in the /wa-position to the alkoxy group. Several additional monosubstituted benzenes and substituted phenols were found to condense with tellurium tetrachloride (Table 7, p. 306). 

Chloroalkyl chloroformates like conventional chloroformates react easily with alcohols, either in the presence of base or simply by heating to give the expected 1- chloralkyl carbonates. 1-Chloroalkylchloroformates react also with phenols, but only in presence of a base to afford 1-chloroalkyl aryl carbonates. 

Mixed aryl and oximido tetrachloroethyl carbonates are crystalline and stable compounds easily obtained by reaction of tetrachloroethyl chloroformate with substituted phenols or N-hydroxy imides as shown in table 3-12. 

Ethyl chloroformate/triethylamine Carboxylic acid aryl esters from carboxylic acids and phenols... 

---