Phase transfer catalysis derivatives

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Most attempts to differentiate these hydroxyl groups with conventional derivatives resulted in the formation of a tetrahydrofuran. The dithiocarbonate can also be prepared by phase-transfer catalysis (Bu4N HS04T, 50% NaOH/H20, CS2, Mel, rt,. 5h) ... 

The preparation of mono- and di-tm-butylcyclopentadienes 1 and 2 starting from monomeric cyclopentadiene was reported first in 1963 [23]. It was noted that the nucleophilic attack of the cyclopentadienide anion on ferf-alkyl halide has to compete with elimination reaction giving isobutene. The yield of the di- and tri-fer/-butylcyclopentadienes 2 and 3 was therefore reported to be modest to low [23, 24], Recently an elegant improvement for this synthesis using phase transfer catalysis was presented (Eq. 1), but the availability of the tri-substituted derivative... 

In the mid-1960s a series of papers by Makosza and Serafinowa (1965, 1966) appeared under the common title Reactions of Organic Anions , in which the catalytic alkylation of phenylacetonitrile and its derivatives carried out in the presence of concentrated NaOH and the catalyst triethylbenzylammonium chloride (TEBA) was described. This was the beginning of phase-transfer catalysis (PTC), and since then thousands of papers haven been published on the subject. 

Nucleophilic substitution of the nitro group in 3-amino 4-nitrofurazan 185 under conditions of phase-transfer catalysis gave a series of acetylene and diacetylene derivatives (Scheme 43) <2001RJ01629>. 

Similar to the Pd-catalyzed pyrrole and thiophene annulations, an intramolecular Heck reaction of substrate 91 resulted in benzofuran 92 [80], Such an approach has become a popular means of synthesizing fused furans. Muratake et al. exploited the intramolecular Heck cyclization to establish the tricyclic core structure en route to the synthesis of a furan analog of duocarmycin SA, a potent cytotoxic antibiotic [81]. Under Jeffery s phase-transfer catalysis conditions, substrate 93 was converted to tricyclic derivatives 94 and 95 as an inseparable mixture (ca. 4 1) of two double bond isomers. 

Epoxidation is another important area which has been actively investigated on asymmetric phase transfer catalysis. Especially, the epoxidation of various (i.)-a,p-unsaturated ketones 68 has been investigated in detail utilizing the ammonium salts derived from cinchonine and cinchonidine, and highly enantioselective and diastereoselective epoxidation has now been attained. When 30 % aqueons H202 was utilized in the epoxidation of various a, 3-unsaturated ketones 68, use of the 4-iodobenzyl cin-choninium bromide 7 (R=I, X=Br) together with LiOH in Bu20 afforded the a,p-epoxy ketones 88 up to 92% ee,1641 as shown in Table 5. The O-substituted... 

General.—The relatively unreactive diethyl arylmethylphosphonates have been used quite successfully in alkene synthesis with phase-transfer catalysis.100 In a comparative study it was shown that anions derived from /S-ketophosphonamides (109) have very low reactivity whereas those from 0-ketophosphonates (110) react quite well with aldehydes to give frwjj-alkenes.101 Benzyl dimethyl phosphonoacetate (111) can be used to form alkenes, e.g. (112), from which the benzyl group can be removed by hydrogenolysis without disturbing the C=C bond.102 The carbanions (113) can be... 

E-(P-Alkylvinyl)phenyliodonium salts react with tetra-n-butylammonium halides to yield the correspondingly substituted Z-haloethenes (80-100% for chloro-, bromo- and iodo-derivatives) [41], In contrast, in the corresponding reaction with Z-(2-benzenesulphonyl-ethenyl)phenyliodonium salts, nucleophilic substitution occurs with retention of configuration to yield the Z-2-benzenesulphonyl-l-haloethenes [42], The ammonium fluorides fail to yield the fluoroethenes, but produce the ethynes by simple elimination [41]. Where carboxylic acids have low solubility in organic solvents, their conversion into the acid chlorides is frequently difficult. Phase-transfer catalysis not only allows the conversion to be effected rapidly, it also results in high yields of a wide range of acid chlorides [43]. 

Phase-transfer catalysis succeeds where the classical method fails in the synthesis of e ,v-3,5-diacctoxycyclopcntene, which is a key compound in prostaglandin synthesis. In contrast with the formation of a mixture of the cis and mrmv-diesters and the 3,4-diacetoxy derivative, e/,v-3,5-diacetoxycyclopcntene is obtained >90% purity from the 3,5-dibromo derivative, when treated with potassium acetate in the presence of a quaternary ammonium salt [4],... 

The ONSH reaction of the carbanion of 2-phenylpropionitrile (45 c) with nitrobenzene in liquid ammonia at -70 °C involves rate-limiting Carom—H bond breaking, as evidenced by the 9.8 times faster rate than for reaction of the analogous substitution of deuterium in 4-<7-nitrobenzene and perdeuterionitrobenzene. Reactions of the carbanion derived from (45c) with 4-chloro-3-trifluoromethylnitrobenzene and 4-chloronitrobenzene in toluene under phase transfer catalysis has also been studied." ... 

A mechanistic study of acetophenone keto-enol tautomerism has been reported, and intramolecular and external factors determining the enol-enol equilibria in the cw-enol forms of 1,3-dicarbonyl compounds have been analysed. The effects of substituents, solvents, concentration, and temperature on the tautomerization of ethyl 3-oxobutyrate and its 2-alkyl derivatives have been studied, and the keto-enol tautomerism of mono-substituted phenylpyruvic acids has been investigated. Equilibrium constants have been measured for the keto-enol tautomers of 2-, 3- and 4-phenylacetylpyridines in aqueous solution. A procedure has been developed for the acylation of phosphoryl- and thiophosphoryl-acetonitriles under phase-transfer catalysis conditions, and the keto-enol tautomerism of the resulting phosphoryl(thiophosphoryl)-substituted acylacetonitriles has been studied. The equilibrium (388) (389) has been catalysed by acid, base and by iron(III). Whereas... 

In the case of carbamoyl derivatives (Y=CONHBu-i) the reactions can be performed even under phase transfer catalysis, by simply treating the aldehyde with the telluronium... 

Glycosyl halides (7a-e) were stereoselectively transformed into l,2-tra s-thio-glycoses by i) (8a-d, 8j) a two-step procedure via the pseudothiourea derivatives [9,10a] the substitution of halide by thiourea is mostly a S l-type reaction since acetylated 1-thio-a-D-mannose (8b) was obtained from acetobromoman-nose (7b) [9cj ii) (8e-i) using thiolates in protic and aprotic solvents [10], or under phase transfer catalysis conditions [11]. Another approach involved the reaction of thioacetic acid with 1,2-trans-per-O-acetylated glycoses catalyzed with zirconium chloride [12]. The 1,2-trans-peracetylated 1-thioglycoses (8e-h) were obtained in high yield. No anomerized products could be detected in these reactions (Fig. 1). 

To facilitate accesses to suitably functionalized sialic acid derivatives and complex sialyloligosaccharides for other usehil neoglycoconjugates, phase transfer catalysis (PTC) has been exploited extensively [for reviews see 42]. This process provided a wide range of carbohydrate derivatives under essentially clean Sn2 transformations. In the case of acetochloroneuraminic acid 1, the PTC reactions always provided inverted a-sialic acid derivatives [43]. para-Formylphenyl sialoside 7 [44], together with many other sialoside derivatives such as 8-10 [43], including thioacetate 12 [45] and azide 14 [46], were thus obtained (Scheme 1). Aldehyde 7 and similar glycosides are of particular interest since they could be directly conjugated to protein by reductive amina-tion after suitable deprotection [44]. 

Phase-transfer catalysis was found <1996CHEC-II(7)1> to be successful for N-substitution of the furo[3,2-/ ]pyrrole system. The reaction of 81a with methyl iodide or benzyl chloride gave 81b and 81c derivatives. Methyl 4-acetyl-2-[3-(trifluoromethyl)phenyl]furo[3,2-3]pyrrole-5-carboxylate 82 was obtained by reacting 81a in boiling acetic anhydride (Scheme 6) <2005CEC311>. 

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