Synthesis of chiral oxepanes and pyrans by 3-O-allylcarbohydrate nitrone cycloaddition (3-OACNC)
TL;DR: In this article, the regioselectivity of 3-OACNC was found to depend on the structural nature of the nitrone substitution and stereochemistry at 3-C of the carbohydrate backbone.
About: This article is published in Tetrahedron.The article was published on 2003-06-16. It has received 24 citations till now. The article focuses on the topics: Nitrone & Oxepane.
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TL;DR: In this article, a review of asymmetric 1,3-dipolar cycloaddition reactions involving a variety of heteroylides (or ylide equivalents) and dipolarophiles is presented.
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01 May 2012
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TL;DR: Either oxepane or pyran is formed from 3-O-allyl furanoside derivatives, which constitute the framework of a large number of biologically active compounds and the environmentally friendly, efficient, and highly stereoselective syntheses of these chiral intermediates are still a meaningful pursuit.
Abstract: A highly stereoselective surfactant-catalyzed intramolecular nitrone (formed by dehydration in water) cycloaddition in aqueous media leading to exclusive formation of a single isomer is reported. Either oxepane or pyran is formed from 3-O-allyl furanoside derivatives, which constitute the framework of a large number of biologically active compounds. Therefore, the environmentally friendly, efficient, and highly stereoselective syntheses of these chiral intermediates are still a meaningful pursuit.
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TL;DR: In this paper, the oxime-nitrone tautomerism has been revisited using high-level DFT calculations, and it was found that the isomerization has been more favorable through a bimolecular process involving two molecules of oxime, a finding that argues against the commonly accepted thermal 1,2-H-shift mechanism.
Abstract: The oxime–nitrone tautomerism has been revisited using high-level DFT calculations. The isomerization has been found to be more favorable through a bimolecular process involving two molecules of oxime, a finding that argues against the commonly accepted thermal 1,2-H-shift mechanism. The reaction of arylamidoximes with 1,2-diaza-1,3-dienes to yield the corresponding O-substituted oximes (stable intermediates for the synthesis of 1,2,4-oxadiazine derivatives) was also investigated as a rare case in which O-alkylation is observed in the reaction between oximes and electron-poor alkenes in the absence of a base. Under such conditions the reaction usually proceeds through the nucleophilic attack of the oxime nitrogen to yield the corresponding nitrone. The computational investigation revealed that in the case of arylamidoximes, the pathway involving the less stable but more reactive nitrone tautomer is the predominant mechanism, evidencing for the first time the involvement of a nitrone tautomer in nucleophilic additions of oximes. Validation of the model has been carried out by studying alternative ene-like processes; the dramatically different reactivity predicted for arylamidoximes and unsubstituted oxime are rationalized in terms of steric hindrance.
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TL;DR: The use of modified boron hydrides as selective reducing agents for organic functional g roups has been studied extensively as discussed by the authors, with a focus on reducing a wide variety of organic functional groups with remarkable selectivity.
Abstract: Sodium cyanohydridoborate (NaBH3CN) reduces a wide variety of organic functional groups with remarkable selectivity. The reduction of aldehydes and ketones is p H dependent, the reaction proceeding readily a t pH 3-4. Oximes a re smoothly reduced to alkylhydroxylamines and enamines are reduced to amines under acid catalysis. Reaction of a n aldehyde or ketone with ammonia, primary amine, or secondary amine a t p H -7 i n the presence of BHaCNleads t o primary, secondary, or tertiary amines, respectively, uia reductive amination of the carbonyl group. Reaction of substituted pyruvic acids with ammonia and BH3CNaffords an excellent method for the synthesis of amino acids; l5N labeling can be accomplished by using I5NH3. The hydrogens of BHICNcan be readily exchanged for either deuterium or tritium, thus permitting the synthesis of deuteriumor tritiumlabeled alcohols, amines, and amino acids. onsiderable attention has been devo ted t o t h e The earlier d iscovery o f the reduc ing p o w e r 4 and t h e acid stability5 of l i t h ium cyanohydr idobora t e encourstudy of modified boron hydrides as selective reducing agents for organic functional g roups . 2.3 2127 (1962); (c) R. Paul and N . Joseph, Bull. SOC. Chem. Fr., 550 (1952); (d) H. C. Brown and E. J. Mead, J . Amer. Chem. SOC., 75, 6263 (1953). (3) (a) H. Noth and H. Beyer, Chem. Ber., 93, 1078 (1960); (b) J. H. Billman and J. W. McDowell, J . Org. Chem., 26, 1437 (1961); (C) s. s. White, Jr., and H. C. Kelly, J . Amer. Chem. Soc., 92, 4203 (1970). and references therein. C (1) (a) Alfred P. Sloan Foundation Fellow; (b) National Institutes of Health Predoctoral Fellow, 1968-1970. Taken in part from the Ph.D. Thesis of H. D. D., University of Minnesota, 1970. (2) (a) H. C. Brown and B. C. Subba Rao, J . Amer. Chem. SOC., 78, 2582 (1956); (b) G. R. Pettit and D. M. Piatak, J . Org. Chem., 27, (4) R. F. Borch and H. D. Durst, ibid., 91, 3996 (1969). Borch, Bernstein, Durst Cyanohydridoborate Anion
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