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Showing papers in "Journal of Organic Chemistry in 1991"



Journal ArticleDOI
TL;DR: Tris(2-carboxyethyl) phosphine (TCEP) is a reagent for disulfide reduction in water at pH 4.5 that preferentially reduces more strained disulfides, in accordance with the usual mechanism postulated for reduction by phosphines in water.
Abstract: Tris(2-carboxyethyl) phosphine (TCEP) reduces disulfides rapidly and completely in water at pH 4.5. It preferentially reduces more strained disulfides, in accordance with the usual mechanism postulated for reduction of disulfides by phosphines in water. The reagent can be synthesized conveniently in large quantities by acidic hydrolysis of the commercially available tris(2-cyanoethyl) phosphine

669 citations


Journal ArticleDOI
TL;DR: The conformations of calix [4] arenes can be deduced from the 13 C NMR chemical shift of the methylene groups connecting each pair of aromatic rings.
Abstract: The conformations of calix [4] arenes can be deduced from the 13 C NMR chemical shift of the methylene groups connecting each pair of aromatic rings. Inspection of 24 cases revealed that when the phenol rings beside each methylene are in a syn orientation (i.e., in cone conformations), the methylene signals appear aroung δ31, whereas they appear around δ37 when both phenol rings are anti oriented (i.e., in 1,3-alternate conformations). Steric effects are believed to be the main cause of such large differences

532 citations


Journal ArticleDOI
TL;DR: In this paper, a practical method for the asymmetric epoxidation of cis-β-methylstyrene by commercial bleach with up to 86% success rate was described, which is the state-of-the-art.
Abstract: A practical method is described for the asymmetric epoxidation of cis-β-methylstyrene by commercial bleach with up to 86% ee

446 citations





Journal ArticleDOI
TL;DR: In this paper, a range of highly functionalized organozinc compounds have been synthesized in the presence of Cu(I) salts, which can cross-couple with acid chlorides, conjugatively add to α, β-unsaturated ketones, and regioselectively undergo S N 2' substitution reactions with allylic halides.
Abstract: Highly reactive zinc, prepared by the lithium naphthalenide reduction of ZnCl 2 , readily undergoes oxidative addition to alkyl, aryl, and vinyl halides under mild conditions to generate the corresponding organozinc compounds in excellent yields. Significantly, the reaction will tolerate a spectrum of functional groups on the organic halides. Accordingly, this approach can now be used to prepare a wide variety of highly functionalized organozinc compounds. In the presence of Cu(I) salts, the organozinc compounds cross-couple with acid chlorides, conjugatively add to α,β-unsaturated ketones, and regioselectively undergo S N 2' substitution reactions with allylic halides. They also cross-couple with aryl or vinyl halides with Pd(O) catalysts

326 citations


Journal ArticleDOI
TL;DR: In this paper, Mansuy showed that aziridi-nation of a number of olefins can be achieved with (N- (p-toluenesulfonyl)imino)phenyliodinane (PhI=NTs)2 using Fe(II1)- and Mn(II 1)-porphyrins as catlysts.
Abstract: Summary: The Cu(1)- or Cu(I1)-catalyzed aziridination of both electron-rich and electron-deficient olefins em- ploying (N-do-toluenesulfonyl)imino)phenyliodinane, PhI=NTs, as the nitrene precursor, affords N-tosyl- aziridines in yields ranging between 55%-95%. In a seminal 1967 publication, Kwart and Kahn' re- ported the copper-bronze-catalyzed aziridination and al- lylic insertion reactions of benzenesulfonylazide with cy- clohexene. Subsequently, Mansuy disclosed that aziridi- nation of a number of olefins can be achieved with (N- (p-toluenesulfony1)imino)phenyliodinane (PhI=NTs)2 using Fe(II1)- and Mn(II1)-porphyrins as catlysts.3 Other evidence for catalytic imido group transfer has appeared in the literat~re;~ however, the number of olefinic sub- strates, nitrene precursors, and catalysts that have been evaluated in these studies has been limited. In view of the demonstrated utility of suitably functionalized aziridines in organic synthesis: it is noteworthy that the

324 citations



Journal ArticleDOI
TL;DR: In the absence of magnesium salts (from the synthesis of the reagents), this paper showed that B-allylditerpenylborane reagents (Ter 2 *BCH 2 CH=CH 2, 1-3) react with representative aldehydes (RCHO, R=Me, n-Pr, iPr, t-Bu, vinyl, and Ph) practically instantaneously at −100 o C to give homoallylic alcohols (R*CH(OH)CH 2 CH =CH 2 ) with optical purities approapching 100%
Abstract: In the absence of magnesium salts (from the synthesis of the reagents), our chiral B-allylditerpenylborane reagents (Ter 2 *BCH 2 CH=CH 2 , 1-3) react with representative aldehydes (RCHO, R=Me, n-Pr, i-Pr, t-Bu, vinyl, and Ph) practically instantaneously at −100 o C to give homoallylic alcohols (R*CH(OH)CH 2 CH=CH 2 ) with optical purities approapching 100% ee. The exceptional reaction rate achieved at −100 o C indicates that these allylborations are among the fastest reactions presently known to the organic chemist. The short reaction time adopted (≤0.5 h) greatly facilitates maintaining the reaction temperature at −100 o C. In this way, B-allyldiisopinocampheylborane ( d Ipc 2 BAll, d 1) gives homoallylic alcohols of ≥96-99% ee, B-allylbis(4-isocaranyl) borane (4- d Icr 2 BAll, 2) affords alcohols of ≥98% ee and B-allylbis(2-isocaranyl) borane (2- d Icr 2 BAll, 3) provides alcohols of ≥99% ee

Journal ArticleDOI
TL;DR: In this article, a tetrazole synthesis with a sterically hindered o-tetrazole group was described. But the synthesis was performed by three different routes, one of them employing a new tetrazoles synthesis.
Abstract: 5-[4'-Methyl-1,1'-biphenyl-2-yl]-1H-tetrazole (6), which contains a sterically hindered o-tetrazole group, was synthesized by three different routes, one of them employing a new tetrazole synthesis. Subsequent acid hydrolysis of the trityl protecting group of 5 yielded biphenylyltetrazole 6. The second synthesis involved the nitrosation of an N-(2-cyanoethyl)-protected biphenylamidrazone. The third method involves the novel transformation of an N-(2-cyanoethyl)-substituted amide into the corresponding N-(2-cyanoethyl)-protected tetrazole in one step using triphenylphosphine, diethyl azodicarboxylate (DEAD), and azidotrimethylsilane. Subsequent base hydrolysis of the cyanoethyl group yielded 6 as before. Examples are also provided of the application of this new reaction to other N-(2-cyanoethyl)-protected carboxamides

Journal ArticleDOI
TL;DR: The results indicate that the CD spectroscopic method using 2 as a receptor molecule serves as a nex sensory system for sugar molecules.
Abstract: For the development of receptor molecules that can recognize sugar molecules, we newly synthesized 2,2'-dimethoxydiphenylmethane-5,5'-diboronic acid (2). It was shown that in the presence of 2, D-glucose, D-maltose, D-cellobiose, and D-lactose result in a CD band at 275 nm. The results indicate that the CD spectroscopic method using 2 as a receptor molecule serves as a nex sensory system for sugar molecules

Journal ArticleDOI
TL;DR: In this paper, a stoichiometric amount of iodide plus propylene oxide in the absence of air was shown to be superior to a catalytic amount of iodine in the air.
Abstract: To photocyclize stilbenes, a stoichiometric amount of iodine plus propylene oxide in the absence of air is superior to a catalytic amount of iodine in the air. The propylene oxide prevents HI from photoreducing double bonds. The absence of air prevents photooxidative side reactions, shown in one case to be caused by a photogenerated oxidant, possibly hydrogen peroxide

Journal ArticleDOI
TL;DR: In this paper, the shape selectivity of high-crosslinked polymers is discussed in detail, and the influence of the arrangement of functional groups within the cavities versus the spatial requirements (shape selectivity) on selectivity is discussed.
Abstract: Highly crosslinked polymers are prepared by radical copolymerization of β-D-fructopyranose 2,3:4,5-bis-O-((4-vinylphenyl)boronate) and α-D-galactopyranose 1,2:3,4-bis-O-((4-vinylphenyl)boronate) with a large amount of cross-linking agent. After splitting off the respective templates these polymers were used for racemic resolution of the racemates of the templates with separation factors α as high as α=2.36 in the batch procedures. The influence of the arrangement of functional groups within the cavities versus the spatial requirements (shape selectivity) on selectivity is discussed in detail. In the examples presented here, the orientation of the functional groups inside the cavity is the dominating factor; shape selectivity is only of secondary importance

Journal ArticleDOI
TL;DR: In this article, a variety of novel perfluoroalkyl-substituted compounds in high yields using easily prepared (perfluoralkyl)trimethylsilanes (1a-c) is described.
Abstract: The preparation of a variety of novel perfluoroalkyl-substituted compounds in high yields using easily prepared (perfluoroalkyl)trimethylsilanes (1a-c) is described. (Trifluoromethyl)-, (pentafluoroethyl)-, and (heptafluoropropyl)trimethylsilane, 1a-c, respectively, react readily with carbonyl compounds, such as aldehydes and ketones, by a fluoride-initiated catalytic process. Fluoride-initiated addition of 1 to a carbonyl group generates an oxyanionic species which then further catalyzes the reaction. Even enolizable carbonyl compounds react cleanly under the reaction conditions. A study of the scope of the reactivity of 1a toward other carbonyl groups in esters, lactones and an acid chloride was also carried out



Journal ArticleDOI
TL;DR: Tris(trimethylsily1)silane is an effective reducing agent for organic halides, selenides, xanthatee, and isocyanide, as well as an effective hydrosilylating agent for dialkyl ketones and alkenes as mentioned in this paper.
Abstract: Tris(trimethylsily1)silane is an effective reducing agent for organic halides, selenides, xanthatee, and isocyanide, as well as an effective hydrosilylating agent for dialkyl ketones and alkenes. The silane functions as a mediator in the formation of intermolecular carbon-carbon bonds via radicals and allows a variety of organic substrates to be used as alkyl radical percursors. Absolute rate constants for the reaction of (MeSSi),@' radicals with a variety of organic compounds have been measured in solution by laser flash photolysis. At 294 K rate constants are >5 X 10' M-' s-l for C=C double bonds that are activated by neighboring ?r-electron systems or by electron-withdrawing groups. For other substrates, reactivities decreased in the order xanthate > selenide > isocyanide > nitro > sulfide.


Journal ArticleDOI
TL;DR: In this article, the chiral N,N-dialkylnorephedrine-catalyzed addition of dialkylzincs to aliphatic and aromatic aldehydes afforded secondary alcohols of high optical purity (to >95% ee).
Abstract: The chiral N,N-dialkylnorephedrine-catalyzed addition of dialkylzincs to aliphatic and aromatic aldehydes afforded secondary alcohols of high optical purity (to >95% ee). Among the N,N-di(primary alkyl) norephedrines, N,N-di-n-butylnorephedrine (DBNE, 3d) was found to be the most effective catalyst. 1-Phenyl-2-(1-pyrrolidinyl) propan-1-ol (3i) and N,N-diallylnorephedrine (3j) were also highly effective catalysts. The method described provides optically active secondary aliphatic alcohols of high optical purity which cannot be prepared by conventional methods


Journal ArticleDOI
TL;DR: Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process as discussed by the authors.
Abstract: Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process, and the amounts of chiral ligand and osmium catalyst required diminish dramatically




Journal ArticleDOI
TL;DR: In this article, a two-phase system for monoacylation of α-keto acids by persulfate was proposed, which takes advantage of the difference in basicity and lipophilicity between the starting base and the mono-acylation products.
Abstract: The silver-catalyzed decarboxylation of α-keto acids by persulfate leads to acyl radicals, which can effect the selective homolytic acylation of pyridine and pyrazine derivatives. Compared with the previously developed source of acyl radicals by hydrogen abstraction from aldehydes, this procedure is more effective in monoacylation when multiple positions of high nucleophilic reactivity are available in the heterocyclic ring. Although the introduction of an acyl group strongly activates the heterocyclic ring toward further substitution, monoacylation can be achieved by taking advantage of the difference in basicity and lipophilicity between the starting base and the monoacylation products in a two-phase system

Journal ArticleDOI
TL;DR: A highly efficient chiral ester enolate-imine condensation giving 3-hydroxy-4-aryl-β-lactams with >96% ee is successfully applied to the asymmetric synthesis of the enantiomerically pure taxol C-13 side chain, N-benzoyl-(2R,3S)-3-phenylisoserine, and its analogues.
Abstract: A highly efficient chiral ester enolate-imine condensation giving 3-hydroxy-4-aryl-β-lactams with >96% ee is successfully applied to the asymmetric synthesis of the enantiomerically pure taxol C-13 side chain, N-benzoyl-(2R,3S)-3-phenylisoserine, and its analogues

Journal ArticleDOI
TL;DR: In this article, the diastereofacial selectivity of aldol reactions of α-methyl chiral aldehydes and propionate and ethyl ketone derived lithium and boron enolates is analyzed from the perspective of a transition state model.
Abstract: The diastereofacial selectivity of the aldol reactions of α-methyl chiral aldehydes and propionate and ethyl ketone derived lithium and boron enolates is analyzed from the perspective of a transition state model suggested by Evans in 1982. The dominant stereocontrol element in these reactions, as in the mechanistically related reactions of crotylmetal reagents and α-substituted chiral aldehydes, appears to be the minimization of gauche pentane itneractions in the competing transition states