Triphenylphosphine/hexachloroethane

Treatment of the 2-amino-3-hydroxypyridine 161 with triphosgene resulted in the formation of the l,3-oxazolo[4,5- ]-pyridin-2(37T)-one 162, an intermediate in the formation of CRF-1 receptor ligands (Equation 59) <2005TL1683>. Oxazolo[4,5-, ]pyridines have been synthesized using a triphenylphosphine-hexachloroethane combination, with the triphenylphosphonium halide being formed prior to addition of the amide (Equation 60) <2005TL9001>. 

The triphenylphosphine-hexachloroethane system was also used to form oxazolo[5,4-3]pyridines (Equation 62). The reaction conditions tolerated a wide variety of substituents in the 2-position, and even a sterically bulky group did not decrease dramatically the yield of desired products <2005TL9001>. 

Phosphonylated aminoquinolines are prepared from phosphonylated arylamines obtained as above in refluxing toluene from diethyl 2-phenyl-2-oxoethylphosphonate and arylamines [mixture of the P-imino- and (Z)-P-enamino derivatives]. Metallation of p-unino and p-enaminophosohonates with n-BuLi in THF followed by sequential treatment with isocyanates, triphenylphosphine, hexachloroethane, Et3N, and aqueous workup produces, after deprotection, 3-phosphonylated-4-aminoquinolines (Scheme 7.1 IS). - ... 

The direct conversion of carboxyhc acids and amino alcohols to 4,5-dihydrooxazoles has been achieved in yields of up to 80% using triphenylphosphine, hexachloroethane and triethylamine <93T9353> and in yields up to 97% with boric acid <85JCS(P1)1865>. Amino alcohols react with dimethylformamide dimethylacetal in the presence of Amberlite resin to give the oxazoles in 65-90% yield <9UOCl961>. 

The products of the reaction between alkyldiphenylphosphines and hexachloro-ethane in the presence of a tertiary amine are the ylide (88) and the a-chloro-alkylphosphine (89), which are interchangeable, constitutional isomers that interconvert via an intramolecular reversible 1,2-chlorine shift from phosphorus to carbon. Application of the triphenylphosphine-hexachloroethane reagent for the self-condensation polymerization of / -aminobenzoic acid has been studied in detail. Related reactions between dicarboxylic acids and diamines, conducted in the presence of pyridine, involve the cationic phosphorane (90) as a key intermediate. Replacement of hexachloroethane by hexabromoethane or... 

In this paper we report the synthesis of new AB monomers which have potential for forming polybenzoxazoles with backbone alkane and alkene moities. Application to monomers of the previously developed low-temperature, high-yield condensation procedure (8) employing triphenylphosphine, hexachloroethane and pyridine is described. The soluble aryl-alkyl and aryl-alkenyl polyamides thus obtained were characterized and converted to polybenzoxazoles. Comparisons are presented between polymers obtained by this two-step method and those prepared by traditional methods. 

More recent examples have employed a milder reagent system, triphenyl-phosphine and dibromotetrachloroethane to generate a bromo-oxazoline, which is subsequently dehydrohalogenated. Wipf and Lim utilized their method to transform intermediate 11 into the 2,4-disubstituted system of (+)-Hennoxazole k Subsequently, Morwick and coworkers reported a generalized approach to 2,4-disubstituted oxazoles from amino acids using a similar reagent combination, triphenylphosphine and hexachloroethane. ... 

The action of triphenylphosphine dichloride, generated from triphenylphosphine and hexachloroethane, on tertiary amines leads to phosphonium salts. Triethylamine is converted into 351 and ethyldiisopropylamine gives a mixture of the salts 352 and 353391. 

Heteropolyacids Hi4[NaPsW29MoOno] and H3PMO12O4 have been shown to be efficient catalysts for consecutive condensation of aldehydes with 5-aminopyrazole -carboxamide and cyclization into pyrazolo[3,4-t4pyrimidines <2007MI1467>. The reaction of ethyl 5-acylaminopyrazoles with hexachloroethane and triphenylphosphine in the presence of a base has been recently reported to afford an imidoyl chloride that reacted in situ with ethylamine yielding an amidine in 71% yield that cyclized readily in DMF in the presence of potassium carbonate to yield pyrazolopyrimidines in 65% yield <2007TL3983>. 

Next, we see an alternative method of generating the IMP. In this method, the aza-Wittig reagent is generated from a primary amine, triphenylphosphine, triethylamine and hexachloroethane. In this case, the resultant IMP reacts with the carbonyl of an ester. Unfortunately, slight hydrolysis of the product is observed during this process. 

When primary amines react with a-acylaminoketones the resulting Schiff bases can be cyclized in the presence of phosphoryl chloride, phosphorus pentachloride, or triphenylphosphine and triethylamine in hexachloroethane to give 1-substituted imidazoles (11) (Scheme 2.1.4). The starting a-acyl-aminocarbonyls are readily prepared from a-amino acids by reduction with sodium amalgam [31, 32] or by the Dakin-West reaction [33, 34], which is most conveniently conducted in the presence of 4-(AUV-dimethylamino)pyridine (DMAP) as an acylation catalyst [35 37]. 

The a-acylaminoketimine or a-acylaminohydrazone (10 mmol) and triethyl-amine (3.67 g, 36 mmol) together with hexachloroethane (3.55 g, 15mmol) are treated at —25°C in acetonitrile (30 ml) with triphenylphosphine (3.93 g, 15 mmol). After stirring (5h) at around 23°C, the solid is filtered and washed with a little THF, and the filhate is evaporated to dryness. The residue is treated with 10% hydrochloric acid (40 ml), diluted with water (250 ml) and exhaustively extracted with ether. The aqueous phase is saturated with sodium chloride, made strongly alkaline with solid KOH, and again exhaustively extracted with ether. The dried ether extracts are concentrated, and the residue is either reciystallized or distilled. 

Since the successful use of phenylphosphiiK dichloride 2 [11], hexachloro-cyclotriphosphatriazene 3 [12], triphenylphosphine 4 [13] and diphenylchloro-phosphate 5 [14] in the synthesis of polyesters, Ogata et al. studied direct polycondensation of diacid and diamii in the presence of triphenylphosphine dicMoride (TPPCI2) [15b] which can form in situ when triphenylphosphine is treated with hexachloroethane or when triphenylphosphine oxide interacts with phosgene or oxalyl chloride (Scheme 3) [15a],... 

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