Phase-transfer catalysis conditions

In the initial report by Corey and Chaykovsky, dimethylsulfonium methylide (2) reacted smoothly with benzalaniline to provide an entry to 1,2-diphenylaziridine 67. Franzen and Driesen reported the same reaction with 81% yield for 67. In another example, benzylidene-phenylamine reacted with 2 to produce l-(p-methoxyphenyl)-2-phenylaziridine in 71% yield. The same reaction was also carried out using phase-transfer catalysis conditions.Thus aziridine 68 could be generated consistently in good yield (80-94%). Recently, more complex sulfur ylides have been employed to make more functionalized aziridines, as depicted by the reaction between A -sulfonylimine 69 with diphenylsulfonium 3-(trimethylsilyl)propargylide (70) to afford aziridine 71, along with desilylated aziridine 72. ... 

Under the phase-transfer catalysis conditions, 2-bromo-8-methylquino-line (67) was coupled with 2-pyridylboronic ester 68 to furnish 2-(2-pyridyl)-8-methylquinoline (69) in 56% yield (91JOC6787). At this point, it is opportune to mention that the simple 2-pyridylborane, in contrast to 3- and (4-pyridyl)boranes, is considered an unsuitable Suzuki coupling partner because it forms an unusually stable cyclic dimer resembling a dihydroanthracene. In this case, the obstacle was circumvented by using 2-pyridylboronic ester in place of 2-pyridylborane (Scheme 9). 

Sodium chlorite under phase-transfer catalysis conditions ( CH,Cl,-Na0H-BmNHS04i is also a good choice for the Nef reaction of primary and secondary nitro compounds fEq. 6.10. ... 

The nucleophilic substitution on poly(vinyl chloroformate) with phenol under phase transfer catalysis conditions has been studied. The 13c-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 

Scheme 4.7 O-Alkylation of potassium acetate under phase-transfer-catalysis conditions.

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. 

Allyl chlorides and bromides are readily carbonylated to unsaturated acids using nickel cyanide and phase transfer catalysis conditions. Mechanistic studies revealed that the key catalytic species in this reaction is the cyanotricarbonylnickelate ion(20). 

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... 

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). 

In the synthesis of the -azaebumane series, an intramolecular heteroaryl Heck reaction was the major operation to realize the cyclization <95TL1491>. Under Jeffery s phase-transfer catalysis conditions, the -azaebumane skeleton 105 was prepared from bromopyridine 104. The migratory insertion occurs onto the C(2) position of the indole ring. 

Compounds 31c and 153 were obtained by direct substitution of the in tf/ -prepared sodium salt of 31a in dimethylformamide (DMF Scheme 15). This method was more efficient <1999CCC321> than the preparation of 31b and 31e from 31a under phase-transfer catalysis conditions <1997MOL69>. 

Phase-transfer catalysis conditions can be used for the synthesis of thienothiopyrans from 4-chlorophenylmethylene-malononitriles in a sequence of reactions shown in Scheme 19 <2001SC475>. 

A series of 3-alkyl- and 3-aryl-7/7-furo[3,2- ]-l-benzopyran-7-ones 78 (linear furocoumarins) was synthesized and evaluated for their photochemical and nonphotochemical crosslink formation with DNA as well as for their spectro-photometric and fluorescent properties, lipophilicity, and ability to photobleach A, A -dimethyl-/)-nitrosoaniline (RNO) after irradiation with UVA light <2002AP187>. The synthesis of the linear furocoumarins (Scheme 10) was a modification of a previously published method in which 7-hydroxy-2//-l-benzopyran-2-ones 76 were converted into / -ketoethers 77 by alkylation with haloketones under phase-transfer catalysis conditions. Base-catalyzed intramolecular condensation and subsequent acidification gave the corresponding 78. A molecular complex between each one of these fluorescent furocoumarins and DNA was observed, but only compounds with a 3-Me or 3-Ph group showed UVA irradiation-induced crosslink formation. 

Even moisture-sensitive compounds can be used as substrates, although with a lesser yield in phase-transfer catalysis conditions than in stoichiometric transformations536 (reaction 268). 

Phase transfer catalysis conditions have also been applied to the N-alkylation of lactams.132-134... 

Aminocrotononitrile reacts with hydrogen sulfide in an alkaline medium under phase transfer catalysis conditions and gives mainly 4-thiapyranone (239) with 4-thiapyranthione (240) as a minor product. In... 

A biphenyl and ct-methylnaphthylamine-derived chiral quaternary ammonium salt 23d, which was shown by Lygo to be effective for the asymmetric alkylation of Schiffs base 20, was also effective in the Michael reaction (Scheme 7.12) [43]. Notably, the enantioselectivity was highly dependent on the reaction conditions and substrates used. The Michael reaction of imine esters such as benzhydryl and benzyl esters with a,p-unsaturated ketones under solid-liquid phase-transfer catalysis conditions afforded the Michael adduct in up to 94% ee and 91% ee, respectively, while the tert-butyl ester showed moderate enantioselectivity (Scheme 7.12). Interestingly, in contrast to earlier reports, acrylate [42] and acrylamides failed to undergo the Michael reaction under these optimized conditions. 

Rothenberg, G. and Sasson, Y. (1996) Extending the haloform reaction to nonmethyl ketones oxidative cleavage of cydoalkanones to dicarboxylic adds using sodium hypochlorite under phase transfer catalysis conditions. Tetrahedron, 52, 13641. 

Condensation of dibromomethane with the 1,2,4-triazepine 194 in phase-transfer catalysis conditions provides efficient and facile access to the biheterocyclic triazepine 42 with high regioselectivity (Equation 19) <1997TL2087>. 

The photostimulated carbonylation of aryl and vinyl halides by Co(CO)4" ions under phase-transfer catalysis conditions [Co2(CO)8, C6H6/NaOHaq, CO, Bu4N+Br", 65 °C] has been reported211,212. Thus PhBr, o- and /7-bromo toluenes, /7-bromoanisole, p-bromofluorobenzene, 4-bromoacetophenone and 1- and 2-bromonaphthalenes gave ArC02Na in 90-98% yields. Under the conditions used, carbonylation did not occur with unsubstituted PhCl, but when it was substituted, as in / -chlorobenzoic acid, or p-chlorophenylacetic acid, carbonylation was quantitative (98% yield). 

One of the most interesting applications of the photostimulated carbonylation of aryl halides by Co(CO)4 ions under phase-transfer catalysis conditions is the synthesis of benzolactams and lactones 293 starting from aryl halides bearing amino or hydroxy groups on a side chain ortho to the halogen (equation 180)212. 

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