A mechanistic study of the reactions of azines and other analogous C=N systems with some oxygen-transfer agents PDF
Preview A mechanistic study of the reactions of azines and other analogous C=N systems with some oxygen-transfer agents
AMECHANISTICSTUDYOFTHEREACTIONSOFAZINESANDOTHER ANALOGOUSC=NSYSTEMSWITHSOMEOXYGEN-TRANSFERAGENTS By RODRIGOPAREDES ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOLOFTHE UNIVERSITYOFFLORIDAINPARTIALFULFILLMENTOFTHE REQUIREMENTSFORTHEDEGREEOFDOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1991 DEDICATEDTOMYFOURWOMEN, Cielito,Jeanne,XimenaandJuliana, and TOTHEMEMORYOFMYUNFORGETTABLEFRIEND, Holger ACKNOWLEDGEMENTS ItiswithmuchgratitudethatIacknowledgetheguidanceandadviceof ProfessorWilliamR.Dolbier,Jr.inmyPhDendeavor. Ifithadnotbeenforhis encouragementandassistance,IwouldnothaveattainedmyPhDatsuchalatestage inmylife. ItwasworththeeffortandIenjoyeditverymuch. Ialsowanttothankthemembersofthesupervisorycommitteefortheir interest,time,andfortheirvaluableadvice. IammostgratefultotheUniversidaddelValleDirectives,especiallyPresident Dr.HaroldRizo,fortheencouragementandfinancialassistancegranted. IacknowledgethefinancingoftheresearchbyCOLCIENCIAS. The dedicationtotheresearcheffortonthepartofAlbaLuciaChavezandtheinvaluable assistancekindlyofferedbyDr.ConradBurkholderaregratefullyacknowledged. IfeelspecialgratitudeforMrs.LindaCannonwhoperformedthecountless tasksthatwentintopreparingthemanuscriptwithsuchpatienceanddedication. Finally,thesupportandencouragementofmyfamilyandcolleagueshavebeen muchappreciated. m - TABLEOFCONTENTS page ACKNOWLEDGEMENTS iii ABSTRACT vi CHAPTERS 1 OXIDATIONOFA7TNESTOAZINEMONOXIDES 1 2 MECHANISTICINTERPRETATIONS OFTHEOXIDATIONSOFAZINES 7 3 OXIDATIONOF4-NITROBENZALDEHYDE-T-BUTYLIMINE, 4-METHOXYBENZALDEHYDE-T-BUTYLIMINE,ACETONE METHYLPHENYLHYDRAZONEANDBENZALDEHYDE METHYLPHENYLHYDRAZONEWITHN-BENZOYLPEROXY- CARBAMICACID 16 4 OXIDATIONOFN-4-NITROBENZYLIDEN-N’-4-METHOXY BENZYLIDENAZINEWITHN-BENZOYLPEROXYCARBAMIC ACIDINTHEPRESENCEOFEXCESSp-TOLUICACID 21 5 OXIDATIONOFN-CYCLOHEXYLIDEN-N’- 4-NITROBENZYLIDENAZINEWITHN-BENZOYL- PEROXYCARBAMICACIDINTHE PRESENCEOFEXCESSp-TOLUICACID 25 6 OXIDATIONOFSYMMETRICALAZINESWITHN- BENZOYLPEROXYCARBAMICACIDINTHE PRESENCEOFEXCESSOFACARBOXYLICACID 29 7 COMPARATIVESTUDYOFTHEOXIDATION OFBENZALDAZINEWITHFIVE DIFFERENTOXYGEN-TRANSFERAGENTS 33 8 CONCLUSIONS 37 IV 9 EXPERIMENTALSECTION 40 GeneralMethods 40 ExperimentalProcedures 40 APPENDIX ACRONYMSUSEDINTHISDISSERTATION 60 REFERENCES 61 BIOGRAPHICALSKETCH 64 v AbstractofDissertationPresentedtotheGraduateSchooloftheUniversityofFlorida inPartialFulfillmentoftheRequirementfortheDegreeofDoctorofPhilosophy AMECHANISTICSTUDYOFTHEREACTIONSOFAZINESANDOTHER ANALOGOUSC=NSYSTEMSWITHSOMEOXYGEN-TRANSFERAGENTS By RodrigoParedes December1991 Chairman: WilliamR.Dolbier,Jr. MajorDepartment: Chemistry Treatmentofimineswithoxidizingagentsleadstotheformationofstable oxaziridines. Hydrazones,whichcanbeviewedasimineswithNboundtotheC=N nitrogen,wouldbeexpectedtoformoxaziridinesupontreatmentwithoxidizing agents. OurresultsindicatethatthepresenceofNboundtotheC=Nnitrogenchanges thecourseofthereactionandinsteadofanoxaziridine,adipolarionisformedasthe firstintermediate. Severalproductscanderivefromthesedipolarionsdependingon theirnatureandonreactionconditions. Azines,alsoimineanalogs,shouldalsoform oxaziridinesupontreatmentwithoxidizingagents. Theevidencepresentedinthis dissertationindicatesthatonceagaininthiscase,adipolarionisformedasthefirst intermediateinsteadofanoxaziridine. Acommonreactionofthesedipolarionsis decompositionintocarbonylanddiazocompounds. Thelattercanbefurtheroxidized byexcessoxidizingagenttoasecondcarbonylcompound. Inthepresenceofa vi Vll carboxylicacid,thediazocompoundistrappedtogeneratethecarboxylicacidester. Asyntheticapplicationofthisreactionistheselectivereductionofonecarbonylgroup inopen-chaindicarbonylcompounds. Thestrategyinvolvestheinitialconversionof thedicarbonylcompoundintocyclicazine. Theazineisthentreatedwithan appropriateoxidizingagentinthepresenceofexcessofasuitablecarboxylicacidto giveaketoesterasfinalreducedspecies. Phenyl-substitutedazinestreatedwith oxidizingagentsformaromaticazinemonoxidesincompetitionwithformationofthe carbonylcompound. Thesemonoxidescanbederivedeitherfromtheintermediate oxaziridineorbydirectelectrophilicattackoftheoxidizingagentontheazine nitrogen. Theevidencepresentedinthisdissertationisconsistentwiththelatter mechanism. CHAPTER1 OXIDATIONOFAZINESTOAZINEMONOXIDES Theperacidoxidationofazinestothevariousproductsobservedhasnotbeen studiedfromamechanisticpointofview. Therefore,wethoughtitwouldbeworth theattemptforthisstudy. Theaimoftheworkinthisdissertationistotrytogain understandingofthechemistryinvolvedintheoxidationofazinesandotheranalogous C=Nsystemswithvariousoxygen-transferagents. Ourresearchgrouphasbeeninterestedinthethermalreactivityand photochemistryofazinemonoxidesforalongtime.1’2 Thus,wehavebeeninterested innew,potentiallyusefuloxygen-transferreagentsforthesynthesesofazine monoxidesfromazines. Inthisregard,itwasfoundthatbufferedtrifluoroperacetic acidwasusefulinthepreparationofanumberofphenylsubstitutedazinemonoxides, i.e.2aand2b,whileforthealkyl-substitutedanalogues,onlydecompositionproducts wereobtained(Scheme1).^ Althoughnointermediateazinemonoxidewasabletobe detectedinthelattercase,itwasconsideredreasonablethatonemighthavebeen formedandthenundergoneacidcatalyzeddecompositiontotheproductsobserved (Scheme2). Phenyl-substitutedazinemonoxideswouldbeexpectedtobemorestabledue totheresonancestabilizationprovidedbythephenylgroup(Figure 1). 1 2 0 RR'C=N—N=CRR' CF3CQ3H,Na2CQ3 RR’C=1N—N=CRR' Et20 + la R=R'=Ph 2a (91%) lb R=Ph,R'=H 2b (83%) lc R=nC3H7R'=H nC3H7CHO+nC4H9020CF3 Scheme 1 H H—O—CI—nPr NI NII + N INII+ n—PrCHO + H—CI—nPr cf3co2 CF3C02CH2nPr + N2 HI Scheme 2 3 Onthebasisofourvisualizationofthereaction,weconcludedthatifthe presenceofacidscouldbeavoided,theconversionofalkyl-substitutedazine monoxidestoundesirableproductsmightwellbepreventedandthustheseelusive azinemonoxidescouldbeprepared. Therefore,webecameinterestedinsearchingfor aneffectiveoxidizingagentforacid-sensitivesystems. OxidationofazineswithN-benzoylperoxycarbamicacid. N-benzoylperoxy- carbamicacid(BPC)wasreportedbyRebekandotherstobeaneffectiveepoxidation agentwiththeadvantageovertypicalperacidsthatityieldsasco-productsonly neutralmoieties. Thismadeitapotentiallyveryusefulreagentfordealingwith possibleacid-sensitivesystemssuchasouralkyl-substitutedazinemonoxides. Atthat pointweviewedthereactionofBPCwithazinestoproduceazinemonoxidesasan electrophilicattackbythehydroxyoxygenofBPC3onanitrogenlonepairofthe azine(Scheme3). — Scheme 3 ^ C—NH2 Likeotherhydroperoxyoxygen-transferagents,BPCisverysensitivetothe mediumofreaction,being200timesmorereactiveinaproticsolventssuchasCHCl^ thanitisinhydrogen-bondingsolventssuchasTHForalcohols.^ Thehigher reactivityinaproticsolventscanbeattributedtoamorereadyoxygen-transferaction
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