LECTURE5REACTIONSHYDROXYLGROUPSPARTI
LECTURE'5 REACTIONS'HYDROXYL' GROUPS'PART'I
NOTHING NEWORMYSTERIOUSThe complications arise only because ofthere are so many of them!!As nucleophiles, analog to non-sugar alcoholsThe majority of the chemistry is related to theformationofestersandethers
NOTHING'NEW'OR'MYSTERIOUS' The$complica,ons$arise$only$because$of$ there$are$so$many$of$them!!$ As$nucleophiles,$analog$to$non9sugar$alcohols$ The$majority$of$the$chemistry$is$related$to$the$ forma,on$of$esters$and$ethers.$
CarboxylateestersAcetates -O(CO)CH3 or -OAcBenzoates -O(CO)C,Hs or -OBzSulfonateestersTosylate -O(SO2) C,H,CH, or -OTsMesylate -O(SO,) CH, or -OMsTriflate -O(SO,) CF, or -OTfEthersBenzyl -OCH,C.H, or -OBnTrityl -OC(C,H,)3 or -OTrTrimethylsilyl -OSi(CH,)3 or -OTMSTert-butyldimethylsilyl -OSi(CH3)2(C(CH3)3) or -OTBSor-OSiMe,But or -OTBDMSTert-butyldiphenylsilyl -OSi(C,H,)2(C(CH3)3) or -OTBSor-OSiPh,Butor-OTBDPS
Carboxylate$esters$ Acetates$–O(CO)CH3$or$–OAc Benzoates'–O(CO)C6H5$or$–OBz Sulfonate$esters$ Tosylate –O(SO2)$C6H4CH3$or$–OTs$ Mesylate –O(SO2)$CH3$or$–OMs$ Triflate –O(SO2)$CF3$or$–OTf Ethers$ Benzyl'–OCH2C6H5$or$–OBn Trityl –OC(C6H5)3$or$–OTr Trimethylsilyl$–OSi(CH3)3$or$–OTMS$ TertFbutyldimethylsilyl$–OSi(CH3)2(C(CH3)3)$or$–OTBS$ $$or$–OSiMe2But $or$9OTBDMS$$ TertFbutyldiphenylsilyl$–OSi(C6H5)2(C(CH3)3)$or$–OTBS$ $$or$–OSiPh2But $or$9OTBDPS$$
OHOHOHCHO-CHOHOOHOOHOHOHOHOHOHanomeric OH-1secondary OH-2,3,4primary OH-6
O HO OH OH OH HO primary OH-6 O HO OH OH OH HO secondary OH-2,3,4 O HO OH OH OH HO anomeric OH-1
The functionality at the anomeric center can reactin two waysas an alcohol or as an aldehydeOHOHOHHOOHOHOOHHOHOHIOMeact as aldehyde to form acetal.OHEffectively protect theOH福HO福HOanomericcenterandpreventsHO.OHHOOHIOHfurtherreactivityHO
The functionality at the anomeric center can react in two ways as an alcohol or as an aldehyde act$as$aldehyde$to$form$acetal Effec,vely$protect$the$ anomeric$center$and$prevents$ further$reac,vity$
Equilibrium of α- and β-hydroxyls at the anomeric positionPotential competing inter-conversion betweenαandβformsinter-conversion between Pyranose and furanoseforms
Potential competing inter-conversion between α and β forms Equilibrium of α- and β-hydroxyls at the anomeric position inter-conversion between pyranose and furanose forms
Solubility: very polar in naturevery soluble in polar solvents, especiallywith possible H-bondingInsoluble in non-polar solvents for organicreactions, pdt purification and manipulationSelective protection of particularhydroxyl groups allows the regioselctiverxn of those unprotectedCommon starting point: protect themajority or even all of the free -OH
Solubility: very polar in nature very soluble in polar solvents, especially with possible H-bonding Insoluble in non-polar solvents for organic reactions, pdt purification and manipulation Selective protection of particular hydroxyl groups allows the regioselctive rxn of those unprotected Common starting point: protect the majority or even all of the free -OH
AcetalsEtherAcetylationNucleophilicEsteroxidationSubstitutionReduction
AcetylaKon Acetals Ether Ester Nucleophilic SubsKtuKon oxidaKon ReducKon
AcetalsAcetylationEtherNucleophilicEsteroxidationSubstitutionReduction
AcetylaKon Acetals Ether Ester Nucleophilic SubsKtuKon oxidaKon ReducKon
0000R-CXR-COC-RRCOHacyl halidecarboxylic acidanhydrideEsters: non-nucleophilic and stable to a wide range ofConditionsFrequentlyusedprotectgroupsLess polar than the corresponding alcohols
Esters:$non9nucleophilic$and$stable$to$a$wide$range$of$$ Condi,ons$ Frequently$used$protect$groups$ Less$polar$than$the$corresponding$alcohols$