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OrganicReactionMechanisms-1998:AnAnnualSurveyCoveringtheLiteratureDated December1997toNovember1998.EditedbyA.C.KnipeandW.E.Watts Copyright(cid:182)2003JohnWiley&Sons,Ltd. ISBN:0-471-49017-2 · ORGANIC REACTION MECHANISMS 1998 ORGANIC REACTION · MECHANISMS 1998 An annual survey covering the literature dated December 1997 to November 1998 Editedby A. C. Knipe and W. E. Watts University of Ulster Northern Ireland AnIntersciencePublication Copyright2003 JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester, WestSussexPO198SQ,England Telephone(+44)1243779777 Email(forordersandcustomerserviceenquiries):[email protected] VisitourHomePageonwww.wileyeurope.comorwww.wiley.com AllRightsReserved.Nopartofthispublicationmaybereproduced,storedinaretrieval systemortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying, recording,scanningorotherwise,exceptunderthetermsoftheCopyright,Designsand PatentsAct1988orunderthetermsofalicenceissuedbytheCopyrightLicensingAgency Ltd,90TottenhamCourtRoad,LondonW1T4LP,UK,withoutthepermissioninwritingof thePublisher.RequeststothePublishershouldbeaddressedtothePermissionsDepartment, JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester,WestSussexPO198SQ, England,[email protected],orfaxedto(+44)1243770571. Thispublicationisdesignedtoprovideaccurateandauthoritativeinformationinregardto thesubjectmattercovered.ItissoldontheunderstandingthatthePublisherisnotengaged inrenderingprofessionalservices.Ifprofessionaladviceorotherexpertassistanceis required,theservicesofacompetentprofessionalshouldbesought. OtherWileyEditorialOffices JohnWiley&SonsInc.,111RiverStreet,Hoboken,NJ07030,USA Jossey-Bass,989MarketStreet,SanFrancisco,CA94103-1741,USA Wiley-VCHVerlagGmbH,Boschstr.12,D-69469Weinheim,Germany JohnWiley&SonsAustraliaLtd,33ParkRoad,Milton,Queensland4064,Australia JohnWiley&Sons(Asia)PteLtd,2ClementiLoop#02-01,JinXingDistripark, Singapore129809 JohnWiley&SonsCanadaLtd,22WorcesterRoad,Etobicoke,Ontario,CanadaM9W1L1 Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappears inprintmaynotbeavailableinelectronicbooks. LibraryofCongressCatalogCardNumber66-23143 BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN0-471-49017-2 Typesetin10/12ptTimesbyLaserwordsPrivateLimited,Chennai,India PrintedandboundinGreatBritainbyBiddlesLtd,Guildford,Surrey Thisbookisprintedonacid-freepaperresponsiblymanufacturedfromsustainableforestry inwhichatleasttwotreesareplantedforeachoneusedforpaperproduction. Contributors C. T. BEDFORD Department of Biotechnology, University of Westminster, London W1M 8JS A. J. CLARK DepartmentofChemistry,UniversityofWarwick,Coventry CV4 7AL R. G. COOMBES Chemistry Unit, Institute of Physical and Environmental Sciences, Brunel University, Uxbridge, Middlesex UB8 3PH R. A. COX 16 Guild Hall Drive, Scarborough, Ontario M1R 3Z8 Canada M. R. CRAMPTON ChemistryDepartment,UniversityofDurham,SouthRoad, Durham DH1 3LE B. G. DAVIS Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QY N. DENNIS 3 Camphor Laurel Court, Stretton, Brisbane, Queensland 4116, Australia P. DIMOPOULOS Department of Chemistry, The Open University, Walton Hall, Milton Keynes MK6 6AA A. P. DOBBS Department of Chemistry, The Open University, Walton Hall, Milton Keynes MK6 6AA D. P. G. EMMERSON Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QY J. G. KNIGHT Department of Chemistry, Bedson Building, University of Newcastle upon Tyne NE1 7RU A. C. KNIPE SchoolofBMS,UniversityofUlster,Coleraine,Co.Antrim BT52 1SA P. KOCˇOVSKY´ Department of Chemistry, Joseph Black Building, Univer- sity of Glasgow, Glasgow G12 8QQ A. W. MURRAY Chemistry Department, University of Dundee, Perth Road, Dundee DD1 4HN B. A. MURRAY Department of Applied Science, IT Tallaght, Dublin 24, Ireland J. SHERRINGHAM DepartmentofChemistry,UniversityofWarwick,Coventry CV4 7AL J. SHORTER 29 Esk Terrace, Whitby, North Yorkshire Y021 1PA J. A. G. WILLIAMS ChemistryDepartment,UniversityofDurham,SouthRoad, Durham DH1 3LE v Preface The present volume, the thirty-fourth in the series, surveys research on organic reaction mechanismsdescribedinthe literature datedDecember1997to November1998. In order to limit the size of the volume, we must necessarily exclude or restrict overlap with other publications which review specialist areas (e.g. photochemical reactions, biosynthesis,electrochemistry,organometallic chemistry, surface chemistry andheterogeneouscatalysis).Inordertominimizeduplication,whileensuringacom- prehensivecoverage,theEditorsconductasurveyofallrelevantliteratureandallocate publications to appropriate chapters. While a particular reference may be allocated to more than one chapter, we do assume that readers will be aware of the alternative chapterstowhichaborderlinetopicofinterestmayhavebeenpreferentiallyassigned. Therehasbeenonlyonechangeofauthorsincelastyear.WewelcomeDrC. Bedford asauthorofReactionsofCarboxylic,PhosphoricandSulfonicAcidsandtheirDeriva- tives. He replaces Dr W.J. Spillane, whose major contribution to the series, through provision of expert reviews since 1983, we wish to acknowledge. We regret that publication has been delayed by late arrival of manuscripts, but once again wish to thank the production staff of John Wiley & Sons and our team of experienced contributors (now assisted by Drs J. Sherringham, P. Dimopoulos and D. P. G. Emmerson) for their efforts to ensure that the standards of this series are sustained. A.C.K. W.E.W. vii CONTENTS 1. Reactions of Aldehydes and Ketones and their Derivatives by B. A. Murray .................................................. 1 2. Reactions of Carboxylic, Phosphoric, and Sulfonic Acids and their Derivatives by C. T. Bedford...................................... 35 3. Radical Reactions: Part 1 by A. J. Clark and J. Sherringham........ 117 4. Radical Reactions: Part 2 by A. P. Dobbs and P. Dimopoulos....... 153 5. Oxidation and Reduction by B. G. Davis, D. P. G. Emmerson and J. A. G. Williams.................................................. 217 6. Carbenes and Nitrenes by J. G. Knight............................ 253 7. Nucleophilic Aromatic Substitution by M. R. Crampton............ 275 8. Electophilic Aromatic Substitution by R. G. Coombes.............. 287 9. Carbocations by R. A. Cox........................................ 297 10. Nucleophilic Aliphatic Substitution by J. Shorter................... 323 11. Carbanions and Electrophilic Aliphatic Substitution by A. C. Knipe 349 12. Elimination Reactions by A. C. Knipe............................. 389 13. Addition Reactions: Polar Addition by P. Kocˇovsky´................ 419 14. Addition Reactions: Cycloaddition by N. Dennis................... 453 15. Molecular Rearrangements by A. W. Murray...................... 487 Author index..................................................... 617 Subject index..................................................... 653 ix OrganicReactionMechanisms-1998:AnAnnualSurveyCoveringtheLiteratureDated December1997toNovember1998.EditedbyA.C.KnipeandW.E.Watts Copyright(cid:182)2003JohnWiley&Sons,Ltd. ISBN:0-471-49017-2 CHAPTER 1 Reactions of Aldehydes and Ketones and their Derivatives B. A. MURRAY DepartmentofAppliedSciences,Institute ofTechnologyTallaght,Dublin,Ireland FormationandReactionsofAcetalsandRelatedSpecies ............... 1 ReactionsofGlucosidesandNucleosides........................... 3 ReactionsofKetenes......................................... 4 FormationandReactionsofNitrogenDerivatives .................... 5 Imines ................................................. 5 IminiumIonsand RelatedSpecies............................... 7 Oximes,Hydrazones,andRelated Species ......................... 8 C−CBondFormationandFission:AldolandRelatedReactions ......... 10 Regio-,Enantio-,and Diastereo-selectiveAldolReactions ............... 10 Mukaiyamaand OtherAldol-typeReactions ........................ 11 Allylations............................................... 15 Other AdditionReactions ..................................... 16 Generaland Theoretical...................................... 16 Hydrationand RelatedReactions................................ 18 AdditionofOrganometallics................................... 18 MiscellaneousAdditions ..................................... 22 EnolizationandRelatedReactions ............................... 23 Enolates ................................................ 26 OxidationandReductionofCarbonylCompounds ................... 26 Regio-,Enantio-,and Diastereo-selectiveRedoxReactions .............. 26 OtherRedoxReactions ...................................... 27 Other Reactions ............................................ 28 References ................................................ 29 Formation and Reactions of Acetals and Related Species A comprehensive ab initio computational study of the anomeric effect in 1,3-dioxa systems has been designed to quantify anomeric effects in such compounds.1 Energy changesassociatedwithO-protonation(anddeprotonation,whererelevant)havebeen calculatedfortetrahydropyran, its 2-hydroxyderivative, andfor 1,3-dioxane,together withacycliccomparatorssuchasmethanol,dimethylether,andmethoxymethanol.All majorconformationshavebeentreatedandtheirgeometricparametersquantified.The 3-oxaalkoxides exhibit a preference for axial (n ) over equatorial (n ) protonation, π σ by 2–3kcalmol−1. The COCOC acetals are stronger bases (at the acceptor oxygen) 1 2 OrganicReaction Mechanisms1998 thanthesimpleethers.Thustheanomericeffectplaysanimportantroleinthecharged species. When trifluoroacetaldehyde ethyl hemiacetal [F CCH(OH)OEt] is treated with 3 enamines in hexane at room temperature, it provides a source of the aldehyde under mild conditions.2 Subsequent reaction with the enamine can be used to prepare β-hydroxy-β-trifluoromethyl ketones, F CCH(OH)CH COR. The enamine 3 2 playssuccessiverolesasbase,ammoniumcounterion,andthencarbonnucleophileas the sequence proceeds. Two stereochemically defined isomeric benzaldehyde acetals, (R)- and (S)- ArCH(OMe)(OPri), undergomethyl-for-methoxy nucleophilic substitutiontogive the corresponding isopropyl ethers, ArCH(Me)(OPri), using Me CuLi–BF .OEt .3 The 2 3 2 degree of racemization observed indicated that the major route was S 1, with free N oxonium ion. The method relies on the acetal carbon being the only stereogenic centre. Themechanismofinhibitionofcysteineproteasesbyatetrahydropyranoneinhibitor hasbeenprobedusing13C NMRlabellingstudies.4Thecarbonyl-labelledinhibitor(1; R=CO∗CHBnNHCOCH CH CO Me), is in equilibrium with its hydrate (2). Addi- 2 2 2 tionoftheenzymepapaingivesanew13Csignalconsistentwitha‘hemithioketal’(3). The diastereomers of (1) have been separated, and although their absolute configura- tions have not been established,one of them inhibits the enzyme with aK of 11 µm i (i.e. a binding constant of 9.1×104mol−1). The structure of the enzyme–inhibitor complex is proposed to mimic the tetrahedral intermediate formed during peptide hydrolysis. O HO OH HO S-Enz RHN 13C RHN 13C RHN 13C Enz-SH O O O (2) (1) (3) Methylcyclopropanonehemiacetal(4)undergoesanasymmetricStreckerreactionto give (1R,2S)-(+)-allo-norcoronic acid (5) in good yield and high de.5 The induction depends on the use of a chiral amine [e.g. (S)-α-methylbenzylamine] to control the face on which the intermediate iminium cation (6) is attacked. H OH −CN N+ Me CO H 2 Me OMe Me Me NH H 2 (4) (5) (6) 1 ReactionsofAldehydesandKetonesandtheirDerivatives 3 meso-1,2-Diols have been desymmetrized to their monobenzyl ethers in >99% ee andupto97%yieldbyconvertingthemtotheirnorborneneacetalsandthencarrying out an intramolecular halo-etherification under kinetic control.6 Cyclodextrins slow the rate of hydrolysis of benzaldehyde dimethyl acetal, PhCH(OMe) , in aqueous acid as the substrate binds in the cyclodextrin’s cavity, 2 producing a lessreactivecomplex.7 Addedalternative guestscompete for the binding site, displacing the acetal and boosting hydrolysis. N,N-Dialkylformamide acetals (7) react with primary amines to give the corresponding amidines (8). Kinetics of the reaction of a range of such acetals with ring-substituted anilines—previously measured in neutral solvents such as methanol or benzene8a—have been extended to pyridine solution.8b In pyridine, the reactions areirreversible,withfirst-orderkineticsineachreactant,andmechanisticallydifferent from those in non-basic solvents. Two mechanisms are proposed to explain Hammett plots for a range of anilines, in which the ρ value switches from negative to positive ataσ valueofca0.5.Thepyridinesolventsubstantiallyenhancestherateinthecase of very weakly basic anilines. R1 OR2 R1 N + H2NR3 N (+ 2 R2OH) R1 OR2 R1 N R3 (7) (8) A hypervalent iodine(III) reagent, Ph−I=O, together with TMS-azide, promotes direct α-azidation of cyclic sulfides: the reaction opens up a route to unstable N,S- acetals.9 Reactions of Glucosides and Nucleosides Two azolopyridines (9a, 9b; X=N, CH) have been employed as transition-state analogue inhibitors of retaining β-glycosidases, and of glycogen phosphorylase.10 The roles of catalytic carboxylic acid and carboxylate groups in the β-glycosidases have been calculated; (9a) strongly inhibits such enzymes, while (9b) has a weaker effect. The difference is ascribed to (i) protonation of (9a) by enzymic catalytic acid [versus (9b), which has N replaced by CH] and (ii) a contribution from a charge- dipoleinteractionbetweentheenzymiccatalyticcarboxylatenucleophileandtheazole ring.Theenzyme–inhibitorcomplexeswereshowntobestructure-invariantbyX-ray crystallography. Calculations of the relative contributions of factors (i) and (ii) above tothedifferenceininhibitionproducedbythetwocompoundsagreewellwithkinetic studies with both enzyme types. Thioglycosides are not subject to acid-catalysed cleavage by glycosyl hydrolases: this effect, which allows them to act as inhibitors, is generally ascribed to their lower basicity.11aHowever,calculationsonconformationalchangesinthemodelcompounds 4 OrganicReaction Mechanisms1998 OH N N N O X HO X Me HO OH (9) (10) a; X = N a; X = O b; X = CH b; X = S (10a,10b;X=O,S)accompanyingprotonationindicatethat,whereasprotonationof the acetal leads to spontaneous collapse to the oxocarbenium ion, the corresponding protonation of the thioacetal yields a stable species.11b Substituenteffectsontheendocycliccleavageofglycosidesbytrimethylaluminium havebeenexplainedintermsofacyclicC−H···Ohydrogen-bondedintermediate.12 Reactions of Ketenes 1,2-Bisketenes (11) can decarboxylate and then ring close to give cyclopropenones (12); subsequent further decarboxylation yields alkynes (13).13 A theoretical study shows that the first reaction is favoured by electronegative substituents, whereas electropositive substituents favour the second. The calculations do not indicate con- clusively whether cyclopropenone formation is concerted, or proceeds via a syn- ketenylcarbene (14). O O R1 C O R1 C R1 R2 • C R2 R1 R2 R2 • O (11) (12) (13) (14) Aminationofketenehasbeenstudiedbyabinitiomethods.14Reactionsofammonia, its dimer, and its (mono)hydrate with ketene have been calculated and compared with earlier studies of ammonia (at lower levels of theory), of water, and of water dimer. In general, the results favour initial addition of ammonia to the C=O bond (giving the enol amide), as againstaddition to the C=C bond (which gives the amide directly). Amide formation is compared with the corresponding hydration reaction whereenolacidandacidarethealternativeimmediateproducts.Mostofthereactions, i.e.bothadditionsandtautomerizations,aresuggestedtoinvolvecyclicsix-membered transition states. Hydration of carbodiimide (HN=C=NH) is described under Imines below.