Carbon tetrachloride under Triphenylphosphine

Then, selective halogenation has been carried out at mild conditions under which only the halogenation of the two primary hydroxyl groups occurs. The secondary hydroxyl groups remain intact under these conditions. The reaction proceeds smoothly with carbon tetrachloride and triphenylphosphine in anhydrous pyridine at 5°C for 18 hours (22). 1,6-Dichloro-1,6-dideoxy-3,4-0-isopropyli-... 

Triphenylphosphine in refluxing carbon tetrachloride converts primary and secondary alcohols into the corresponding chlorides under very mild conditions (/) with inversion of configuration (2, J). A suggested route for the transformation is shown. 

Carbon tetrachloride is dried over calcium chloride and distilled before use. Triphenylphosphine is dried by dissolving it in dry benzene, removing the solvent under vacuum, and storing over phosphorus pentoxide. Alcohols should also be dried before use. 

The following procedure is described in U.S. Patent 3,475,407. A solution of 50 g of lincomycin hydrochloride, 120 g of triphenylphosphine, and 500 ml of acetonitrile in a 3 liter flask equipped with a stirrer was cooled in an ice bath and 500 ml of carbon tetrachloride was added in one portion. The reaction mixture was then stirred for 18 hours without addition of ice to the cooling bath. The reaction was evaporated to dryness under vacuum on a 50° to 60°C water bath, yielding a clear, pale yellow viscous oil. An equal volume of water was added and the mixture shaken until all of the oil was dissolved. The resulting suspension of white solid (03PO) was filtered through a sintered glass mat and discarded. The filtrate was adjusted to pH 11 by addition of 6N aqueous sodium hydroxide. A solid precipitated. 

An efficient pathway to 3,8-dihydro derivatives of the same ring system 496 was published by Lee et al. < 1994S1057, 1997S1461 > the ureido ethylidenehydrazones of type 494 were treated with triphenylphosphine in the presence of triethylamine in a carbon tetrachloride solution under refluxing conditions to yield the product 496 in acceptable yields. The transformation was rationalized to proceed via the zwitterionic intermediate 495. It is important to note that, in the cases of R = aryl group, the reaction proceeded in a totally different direction to furnish... 

Hydroxy amides undergo cyclodehydration to oxazolines under very mUd conditions with triphenylphosphine and carbon tetrachloride. Carbon tetrabromide can also be used. The formation of the corresponding p-chloro amide is generally not a significant problem. The major disadvantage is that removal of the byproduct triphenylphosphine oxide may be difficult at times. Representative examples are shown in Table 8.14 (Fig. 8.5).n4,i4o,i73-i8i... 

Halogenations with dihalotriphenylphosphoranes have been reviewed briefly by Fieser and Fieser.4 Dibromotriphenylphos-phorane appears to have been studied somewhat more than the dichloro compound, but both reagents effectively convert alcohols to alkyl halides, carboxylic acids and esters to acid halides, etc. The reaction of 1,2-epoxycyclohexane with dibromotriphenylphos-phorane under conditions similar to those described here gives a mixture of cis- and trans-1,2-dibromocyclohexanes. A reagent prepared from triphenylphosphine and carbon tetrachloride has been used for similar transformations.5... 

A oven-dried, 1-L, round-bottomed flask, equipped with a magnetic stirring bar, is charged with 500 mL of dry THF and 1 -[(dimethyl)phenylsilyl]-1 -hexanol (32.6 g, 138 mmol). Carbon tetrachloride (53.20 g, 33.4 mL, 345.9 mmol) and triphenylphosphine (54.30 g, 207 mmol) are added and the flask is equipped with a condenser and a rubber septum and purged with argon via inlet needle and outlet needle to an oil bubbler.3 The reaction mixture is heated to reflux under argon for 12 hr. After the reaction mixture is allowed to cool to room temperature, the volatiles are removed... 

A perrhenic acid solution is prepared as under Part A and is added to a suspension of 25 g. of triphenylphosphine in 250 ml. of absolute ethanol in a 500-ml. round-bottomed flask fitted with a stirrer and a reflux condenser. The solution is stirred while it is heated to boihng and refluxed for 10 minutes. The soHd is filtered from the hot solution and washed with two 50-ml. portions of ethanol and five 50-ml. portions of diethyl ether. The yield is 12.2 g. (89%) (checkers report 97% yield) of diamagnetic gray-green prisms, m.p. 190 to 198° with decomposition (checkers report 195°), soluble in benzene, chloroform, and dichloro-methane, and insoluble in light petroleum, carbon tetrachloride, and ethanol. Anal. Calcd. for ReOCl2(OEt)-2P — (C H6)3 Cl, 8.4 Re, 22.1. Found (by checkers) Cl, 8.1 Re, 21.4. 

Reaction with ettoUzabk ketones. Triphenylphosphine in carbon tetrachloride reacts with cyclohexanone under reflux to give (1) and (2) in the ratio of 93 7. Simitar... 

Reaction with epoxides. Epoxides react with triphenylphosphine and carbon tetrachloride (reflux under N2 for I 2 hr.) to give the corresponding cts-l,2-dichloro-alkane and triphenylphosphine oxide. Thus cyclohexenc oxide is converted into cis-l,2-dichlorocyclohexane in 80% yield. Only a trace of rran -l,2-dichlorocyclo-hexane is formed. 

It was shown that easily accessible diethyl 1-hydroxyalkylphosphonates 1 can be converted into diethyl 1-chloroalkylphosphonates 2 utilizing triphenylphosphine/carbon tetrachloride, affording high yield and purity under neutral conditions (see Appendix) [241]. 

Triphenylphosphine and its derivatives provide another method of dehydration under relatively mild conditions. Benzamide reacts with triphenylphosphine and carbon tetrachloride in tetrahydrofuran (THF) to form probably the chloro-imine (7) which on warming at 45—55° with more of the phosphine, loses hydrogen chloride [29] an attempt to use pyridine as solvent and to facilitate the removal of the hydrogen chloride, gave a very low yield of nitrile. Under optimum conditions the yield was 83%. 

Unfortunately, alkylation of thallium(i) salts of cyclic 1,3-diketones results in predominant O-alkylation. In a reaction of possibly general applicability to highly enolized ketones, triphenyldibromophosphorane effects the conversion of acetylacetone into 4-bromopent-3-en-2-one under mild conditions. The reaction of enolizable ketones with triphenylphosphine and carbon tetrachloride gives rise to variously halogenated and homologated derivatives. ... 

The synthesis of ureas by reaction of ammonia or aliphatic primary and secondary amines with carbon monoxide at atmospheric pressure under selenium catalysis is noted. The intermediate salt can be oxidized to the sym-urea, or an exchange can be effected with a second amine, leading to unsym-ureas, as shown in Scheme 34. Ureas are readily dehydrated to carbodi-imides by the triphenylphosphine-carbon tetrachloride-triethylamine combination... 

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