Ethers, trichloroethyl

Six protective groups for alcohols, which may be removed successively and selectively, have been listed by E.J. Corey (1972B). A hypothetical hexahydroxy compound with hydroxy groups 1 to 6 protected as (1) acetate, (2) 2,2,2-trichloroethyl carbonate, (3) benzyl ether, (4) dimethyl-t-butylsilyl ether, (5) 2-tetrahydropyranyl ether, and (6) methyl ether may be unmasked in that order by the reagents (1) KjCO, or NH, in CHjOH, (2) Zn in CHjOH or AcOH, (3) over Pd, (4) F", (5) wet acetic acid, and (6) BBrj. The groups may also be exposed to the same reagents in the order A 5, 2, 1, 3, 6. The (4-methoxyphenyl)methyl group (=MPM = p-methoxybenzyl, PMB) can be oxidized to a benzaldehyde derivative and thereby be removed at room temperature under neutral conditions (Y- Oikawa, 1982 R. Johansson, 1984 T. Fukuyama, 1985). 

Deall lation. Chloroformates such as vinyl chloroformates (40) are used to dealkylate tertiary amines. Chloroformates are superior to the typical Von Braun reagent, cyanogen bromide, because of increased selectivity producing cleaner products. Other chloroformates such as aHyl, methyl, phenyl, and trichloroethyl have also been used in dealkylation reactions. Although the dealkylation reaction using chloroformates is mostiy carried out on tertiary amines, dealkylation of oxygen or sulfur centers, ie, ethers or thioethers, can also be achieved. a-Chloroethyl chloroformate [50893-53-3] (ACE-Cl) (41,42) is superior to all previously used chloroformates for the dealkylation reaction. ACE-Cl has the advantage that the conditions requked for ACE... 

The anomeric position of a carbohydrate was protected as its trichloroethyl ether. Cleavage is effected with Zn, AcOH, AcONa (3 h, 92%). ... 

The ether filtrate and washings were evaporated at room temperature under reduced pressure to give a clear liquid residue (801 grams). This residue was distilled under high vacuum to give trichloroethyl phosphorodichloridate (556 grams, 62.4% of theory), boiling point 75°C/0.8 mm. 

The enzymatic synthesis of polyesters from activated diesters was achieved under mild reaction conditions. The polymerization of bis(2,2,2-trichloroethyl) glutarate and 1,4-butanediol proceeded in the presence of PPL at room temperature in diethyl ether to produce the polyesters with molecular weight of 8.2 x 10. Vacuum was applied to shift the equilibrium forward by removal of the activated alcohol formed, leading to the production of high molecular weight polyesters. The polycondensation of bis(2,2,2-trifluoroethyl) sebacate and aliphatic diols took place using lipases BC, CR, MM, and PPL as catalyst in diphenyl ether. Under the... 

PPF catalyzed an enantioselective polymerization of bis(2,2,2-trichloroethyl) tra 5-3,4-epoxyadipate with 1,4-butanediol in diethyl ether to give a highly optically active polyester (Scheme 9). °° The molar ratio of the diester to the diol was adjusted to 2 1 to produce the (-) polymer with enantiomeric purity of >96%. The polymerization of racemic bis(2-chloroethyl) 2,5-dibromoadipate with excess of 1,6-hexanediol using lipase A catalyst produced optically active trimer and pentamer. The polycondensation of 1,4-cyclohexanedimethanol with fumarate esters using PPL catalyst afforded moderate diastereoselectivity for the cis/trans monocondensate and markedly increased diastereoselectivity for the dicondensate product. 

Electron-rich aromatic compounds, such as phenol, anisole and A,./V-dimethylaniline, add to bis(2-trichloroethyl) azodicarboxylate under the influence of lithium perchlorate, boron trifluoride etherate or zinc chloride to yield para-substituted products 74, which are transformed into the anilines 75 by means of zinc and acetic acid86. Triflic acid (trifluoromethanesulphonic acid) catalyses the reactions of phenyl azide with benzene, toluene, chlorobenzene and naphthalene, to give TV-arylanilines (equation 34)87. 

A simple synthesis of 3-substituted and 23-disubstituted 4-chloiofuians was accomplished. It involves a CuCl/bipy-catalyzed regioselective cyclization of l-acetoxy-2.22-trichloroethyl allyl ether followed successively by dechloroacetoxylation with Zn dust and tandem dehydro-halogenation-aromatization with tBuOK/18-crown-6 <99CC2267>. 

The nature of the aromatic substituents is apparently not critical for SSRI activity, as indicated by the structure of duloxetine (23-5), where one ring is replaced by thiophene and the other by naphthalene. The synthesis starts as above by the formation of the Mannich base (23-1) from 1-acetyl thiophene with formaldehyde and dimethyl-amine. Treatment of that intermediate with the complex from lithium aluminum hydride and the 2R,3S entantiomer of dimethylamino-l,2-diphenyl-3-methyl-butane-2-ol gives the S isomer (23-2) in high enantiomeric excess. Treatment of the aUcoxide from (23-2) and sodium hydride with 1-fluoronaphthalene leads to the displacement of halogen and thus the formation of ether (23-2). The surplus methyl group is then removed by yet another variant of the von Braun reaction that avoids the use of a base for saponifying the intermediate urethane. Thus, reaction of (23-3) with trichloroethyl formate leads to the A -demethylated chlorinated urethane (23-4). Treatment of that intermediate with zinc leads to a loss of the carbamate and the formation of the free secondary amine duloxetine (23-5) [23]. 

Trichlorfon can be synthesised in three stages the preparation of trichloroacetic aldehyde (chloral) the production of 0,0-dimethyl ether of phosphorous acid (dimethylphosphite) the synthesis of 0,0-dimethyl(l-hydroxy-2,2,2-trichloroethyl)phosphonate (trichlorfon). 

A variety of 3-substituted furans, including the natural perillene and dendrolasin, are obtained in good yields via reductive annulation of 2,2,2-trichloroethyl propargyl ethers... 

A solution of 2,2,2-trichloroethyl propargyl ether (1 mmol) in THF (2 ml) was added to a stirred, room-temperature suspension of dry CrCl3 (15 mol%), Mn powder (4 mmol), and freshly distilled TMSC1 (4 mmol) in THF (8 ml) under an argon atmosphere. After the addition, the reaction mixture was heated at 60 °C. After 12 h, the reaction mixture was cooled and quenched with water, and extracted three times with ether. After removal of the solvent, the residue was chromatographed on silica gel to give a product in 85% yield [97]. 

Fig. 36 Chromium(II)-catalyzed cyclizations of propargylic 2,2,2-trichloroethyl ethers to 3-substituted furans...

The mixture is then subjected to steam distillation until no more trichloroethyl alcohol passes over. About 4 1. of distillate is obtained (Note 6). The oil is separated from the aqueous layer and the latter is salted out by saturating with sodium sulfate and extracted with three 200-cc. portions of ether. The ether solution is added to the main portion of the alcohol and the whole is dried over anhydrous sodium sulfate. 

The ether is removed by distillation and the product distilled under reduced pressure (Note 7). There is obtained 215 g. (84 per cent of the theoretical amount) of trichloroethyl alcohol boiling at 94—97°/125 mm. and melting at 16-17° (Note 8). A purer compound can be obtained by refractionation under reduced pressure and pressing out the crystals on a cooled porous plate. Pure trichloroethyl alcohol has a melting point of 190 (Note 9). 

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