Aryl chloroformates

Alkali Metal Hydroxides. Addition of base to aqueous chloroformates cataly2es hydrolysis to yield the parent hydroxy compound (11). However, the use of a stoichiometric amount of alkaU metal hydroxides can lead to the symmetrical carbonate, especially from aryl chloroformates (12,13). 

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). 

Acylation. Aryl chloroformates are good acylating agents, reacting with aromatic hydrocarbons under Eriedel-Crafts conditions to give the expected aryl esters of the aromatic acid (38). 

When cysteine reacts with an alkyl or aryl chloroformate, both the -SH and -NH groups are protected, as a thiocarbonate and as a carbamate, respectively. Selective or simultaneous removal of the protective groups is possible. (See cleavage conditions 3-6 for an S-benzyloxycarbonyl derivative, page 485.)... 

See aryl chloroformates water See related ACYL halides... 

Spontaneous hydrolyses of carboxylic anhydrides, diaryl carbonates and aryl chloroformates are faster in cationic than in anionic micelles, regardless of the nature of the counteranion in the cetyltrimethylammonium micelle (Al-Lohedan et al., 1982b Bunton et al., 1984). This charge effect does not seem to be related to substrate hydrophobicity, although the extent of micellar inhibition (relative to reaction in water) is clearly dependent upon substrate hydrophobicity for anhydride hydrolyses. 

Examples of this behaviour are shown in Table 7 where k+ is related to reaction of substrate fully bound to a CTAX micelle and k to reaction in an anionic micelle of SDS. The ratio k+/k is consistently larger than unity for hydrolyses of open chain anhydrides, diaryl carbonates and aryl chloroformates. In addition hydrolysis of 4-nitrophenyl chloroformate is slightly faster in cationic micelles than in water. Spontaneous hydrolyses of N-acyl triazoles are also inhibited less by cationic micelles of CTABr than anionic micelles of SDS (Fadnavis and Engberts, 1982). 

During the preparation of aryl chloroformates, it is essential to keep the reaction mixture really cold during water washing to prevent vigorous decomposition. Phenyl and naphthyl chloroformates may be distilled, but benzyl chloroformate is too thermally unstable. 

C-Activated esters 6 are prepared by reacting hydrazides 4 with aryl chloroformates 5 (X=Q) or carbonic diesters 5 (X=OAr),M whereas N-activated esters 9 are obtained by reaction of the free amino group of N-terminal amino acid 7 or azaamino acid residues with the same reagents. 

Treatment of 7 with acid chloride at — 60 °C in the presence of TiCLt gives the corresponding coupling product 89 stereoselectively (equation 67)40. The reaction of aryl chloroformate with allylsilane in the presence of aluminum trichloride gives aryl 4-alkenoates 90 in excellent yield (equation 68)137. 

Solvolysis rates of isopropenyl chloroformate, CH2=C(Me)0C(0)Cl, were shown to be very similar to those for 4-nitrobenzoyl chloride in mechanism and reactivity.29 Stepwise mechanisms were observed in the aminolysis of aryl chloroformates by a series of substituted quinuclidines - which were more reactive than isobasic secondary alicyclic amines.30 The pH-independent hydrolysis of 4-nitrophenyl chloroformate in MeCN-H20 mixtures proceeded via a cyclic transition state containing the ester and two water molecules.15 Solvolyses of 2-furancarbonyl chloride in most... 

See ARYL CHLOROFORMATES Water See related ACYL HALIDES... 

Arenecyclopentadienyliron(ii) picrates, 44 Arenediazo aryl sulfides, 44 Arenediazoates, 44 Arenediazonium oxides, 44 Artificial fingernails, 45 Aryl chloroformates, 45 2-Arylideneamino-4,6-dinitrophenol salts, 45 Arylmetals, 45... 

Attempts to apply the thermal decarboxylation reaction in the liquid phase to aromatic halofor-mic acid esters have shown that their reaction is different from that ol the aliphatic haloformates. It was found that evolution of carbon dioxide occurs, but only high boiling products could be isolated.136 On heating in the presence of aromatics and Lewis acids, aryl chloroformates do not react to give chlorinated aromatics with concomitant decarboxylation, but undergo a Friedel-Crafts reaction to give phenyl benzoates.137 Under similar conditions phenyl fluoroformate undergoes only polymerization and carbonate formation.137... 

The more reactive alkyl or aryl chloroformates can be used to produce 2-oxopurines under milder conditions than those obtained in urea fusions. Xanthine for example resulted from the aminoimidazolecarboxamide and ethyl chloroformate at 0 °C followed by cycliza-tion of the intermediate urethane (343), either by fusion or by heating with aqueous ammonia (Scheme 137) (sojbQ 185)439). 

Haloaromatic compounds. Aryl chlorides are obtained by heating aryl chloroformates with AICI3 at 200°. For the preparation of the fluorides the chloroformates are treated with excess anhydrous HF (liquid-phase fluorination-decarboxylation). 

A general method of synthesis of the aryl chloroformates involves the reaction of phosgene with phenoxide, M[OAr], dissolved in a suitable solvent at low temperatures [1442] ... 

During the preparation of aryl chloroformates, it is essential to keep the reac-... 

The reaction of silylated fluoromethylphosphonate carbanions with a large variety of alkyl, vinyl, or aryl chloroformates or with carbon dioxide proceeds smoothly at low temperature to give silylated l-(alkoxycarbonyl)-l-fluoromethylphosphonates and 1-(hydroxycarbonyl)-1-fluoromethylphosphonate, respectively (Scheme 3.58). For the electron-withdrawing carboxyl group, the traces of base already present in the reaction medium are sufficient to effect a desilylation if EtOH is added to the mixture. The desilylated products are isolated in 80-91% yields." - " The addition of EtOLi leads to decomposition with loss of phosphate. 

The Michaelis-Arbuzov reaction is generally applicable to the preparation of dialkyl alkoxy- or aryloxycarbonylphosphonates from trialkyl phosphites and alkyl or aryl chloroformates. The reaction proceeds on heating when alkyl or aryl chloroformate is added to trialkyl phosphite at a rate that will maintain a steady evolution of alkyl chloride. The reaction has been performed with a great variety of trialkyl phosphites and alkyl or aryl chloroformates to provide the corresponding phosphonoformates in good to excellent yields (64-97%, Scheme 8.1). ... 

A. J. Deeming, B. L. Shaw, Oxidative addition of alkyl ot aryl chloroformates to the complexes [IrCl(CO)L2](L = dimethylphenyl-phoshine ot -arsine, or trimethylphosphine). Iridium-carboxy- complexes, J. Chem. Soc. A. (1969) 443-448. 

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]. 

Tab. 4.2. Hydantoins 26 synthesized from non-commercially available alkyl and aryl chloroformates prepared with triphosgene [24],...

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