CHEM 236 Reactions

Hydrohalogenation

• Reactants: H-X

• Markovnikov reaction

• regioselective, since X- can attack front/back

• relies on rearrangement of carbocation for most stable

Hydrohalogenation + Peroxide

• Reactants: H-X and ROOR

• Anti-Markovnikov reaction

• free radical addition

Acid-Catalyzed Hydration

• Reactants: H20/H2SO4

• Markovnikov reaction

• H2O/H2SO4 creates H3O+ active species; creates alcohol

• relies on stable carbocation; keep in mind excess H2O drives reaction

Hydroboration-Oxidation

• Reactants: 1) BH3, THF 2) OH-, H2O2, H2O

• Anti-Markovnikov reaction

• no carbocation; H2O2 + OH- create HOO- active species that attacks tri-branch B

• one branch breaks, creates ester with B and breaks off, H2O protonates to create alcohol

Oxymercuration-Demercuration

• Reactants: 1) Hg(OAc)2, H2O 2)NaBH4

• Markovnikov reaction

• no carbocation formed, 3-membered ring created

• Hg(OAc)2 creates Hg(OAc)+ ion; NaBH4 purpose to remove that ion

• H2O attacks most substituted carbon because of resonance

Ozonolysis

• Reactants: 1) O3 2) Me2S, Zn/HOAc

• cleave double bond, add O

Halogenation

• Reactants: X2, inert solvent (CCl4)

• no Markovnikov reaction

• forms 3-membered ring; X- attacks more substituted carbon

• make sure to show stereochemistry

Halohydrin Formation

• Reactants: X2, H2O (or alcohol)

• Markovnikov reaction

• adds alcohol group to most stable carbon (or R group if alcohol is used instead of H2O)

• there’s so much H2O, that it outcompetes the X- ion produced

Grignards

• Reactants: Mg⁰, Et₂O

• general formula R-Mg-X; react with alkyl halide

• purpose = carbanions (carbon nucleophiles to form C-C bonds)

Organolithiums

• Reactants: 2 equivalents of Li⁰, anhydrous solvent (Et₂O)

• general formula R-Li; react with alkyl halide

• purpose = carbanions (carbon nucleophiles to form C-C bonds)

E1, E2, SN1, SN2

• Is base/nucleophile strong?

• What is the structure of the substrate?

• What temperature is the reaction happening at?

• E1, E2 form alkenes; SN1, SN2 substitute groups

• E1, SN1 form carbocations; E2, SN2 happen concertedly

• Stereochemistry: SN1 = racemic, SN2 = inverted, E2 = stereospecific (cis/trans)

Carbenes

• Reactants: diazomethane, dichlorocarbene

• purpose = cycloproponation by reacting with alkenes

• stereospecific, concerted reaction

Dehydration of Alcohols

• Reactants: H₂SO₄, Heat

• purpose = turns alcohol into alkenes

• makes -OH into good LG (H₂O); β-hydrogen gets deprotonated

Halide Conversion from Alcohol

• Reactants: H-X

• purpose = converts alcohol to alkyl halide

• makes -OH into H₂O, then X^- attacks via SN2

Sulfonate Esters

• Reactants = mesylate, tosylate, triflate

• purpose = better way to make alkyl halides without carbocation forming

• know structures and mechanism

Jones Oxidation

• Reactants: CrO₃, H₂SO₄, H₂O, acetone

• purpose = turns primary alcohol/aldehyde to carboxylic acid; secondary alcohol to ketone

PCC Oxidation (Pyridinium Chlorochromate)

• Reactants: PCC, CH₂Cl₂ or DCM

• purpose = turn primary alcohol to aldehyde; secondary alcohol to ketone

  

DMP Oxidation (Dess-Martin Periodinane)

• Reactants: DMP, CH₂Cl₂ or DCM

• purpose = greener way to turn primary alcohol to aldehyde; secondary alcohol to ketone

KMnO₄ Oxidation

• Reactants = KMnO₄, HCl

• purpose = similar to Jones Oxidation, very strong oxidizing agent

Benzylic/Allylic Oxidation

• Reactants: MnO₂

• purpose = selectively target benzylic/allylic alcohols and oxidize them to ketones

Epoxides

• HOW TO MAKE: alkene reacts with mCPBA

• purpose = extend carbon chain +2 to get primary alcohol; acid/base-controlled SN reactions

• acidic conditions = halide attacks more substituted carbon

• basic conditions = halide attacks less substituted carbon

Williamson Ether Synthesis

• Reactants = alkoxide, primary halide/tosylate (or mesylate/triflate)

• purpose = start with alcohol, create ether via SN2

• can use this to make diethyl ethers

Thioether Synthesis

• Reagents = 1) NaOH 2) R-OTs (or another good LG)

• purpose = makes thiol into thioether via SN2

• same mechanism as Williamson Ether Synthesis

Alkoxymercuration-Demercuration

• Reactants = 1) Hg(OAc)₂, alcohol 2) NaBH₄

• purpose = makes an ether at the Markovnikov position of alkene

• same mechanism as Oxymercuration-Demercuration

Cuprates

• HOW TO MAKE: organolithium reacts with 2 equivalents of CuI in THF

• general formula = R₂CuLi

• purpose = milder reagents compared to Grignards/Organolithiums to create C-C bonds

Dihydroxylation

• Reagents = 1) OsO₄, THF 2) H₂S or NaHSO₃

• purpose = turns alkene into glycol by adding -OH to each end

• can have syn- or anti-; to get alcohols anti-, requires turning alkene into epoxide, then opening it up with acid to invert one of the carbons on the alkene

Glycol Cleavage

• Reagents = 1) HIO₄ 2) Pb(OAc)₄

• purpose = cleaves carbon chain of glycol to yield ketones of each half (alcohol turns into carbonyl group)

Sulfur Oxidation

Disulfide Formation

• Reagents = 2 equivalents of thiol needed; 1) NaOH 2) I₂ (oxidative agent)

• purpose = create R-S-S-R chain

• NaOH deprotonates the 2 thiols to get 2 thiolates, then connect together using I₂ as oxidative agent