Alkene Addition Reactions

• These notes cover addition reactions, alkyne reactions, and related mechanisms.

Addition Reactions Overview

• Addition reactions involve adding two groups across a double bond.
• These reactions can form carbocations, potentially leading to rearrangements.

Hydrohalogenation

• Reaction: An alkene reacts with HX (X = Cl, Br, I) in ether.
• Product: An alkyl halide forms with the halogen attached to the more substituted carbon (Markovnikov selectivity).
• Regioselectivity: Follows Markovnikov's rule.
• Stereospecificity: Not applicable (N/A).

Acid-Catalyzed Hydration

• Reaction: An alkene reacts with H₂SO₄ and H₂O.
• Product: An alcohol.
• Regioselectivity: Markovnikov.
• Stereospecificity: N/A.

Modified Acid-Catalyzed Reaction

• Reaction: An alkene reacts with H₂SO₄ and HOCH₃.
• Product: An ether.
• Regioselectivity: Markovnikov.
• Stereospecificity: N/A.
• Carbocation rearrangements can occur in the above reactions that form carbocations (hydride, methyl, or ring shifts).

Anti-Addition Reactions Overview

• Anti-addition reactions add two groups on opposite sides of the double bond without carbocation rearrangement.

Halogenation

• Reaction: An alkene reacts with X₂ (X = Cl, Br) in CH₂Cl₂.
• Product: A vicinal dihalide forms with anti-stereochemistry.
• Regioselectivity: Markovnikov.
• Stereospecificity: Anti.

Modified Halogenation - Halohydrin Formation

• Reaction: An alkene reacts with X₂ (X = Cl, Br) and H₂O.
• Product: A halohydrin (halogen and alcohol) forms with anti-stereochemistry.
• Regioselectivity: Markovnikov.
• Stereospecificity: Anti.

Modified Halohydrin Formation (Alkene to Halogen + Ether)

• Reaction: Alkene reacts with Br₂ and CH₃OH.
• Product: Haloether.
• Regioselectivity: Markovnikov.
• Stereospecificity: Anti.
• Only displays stereochemistry if an achiral center is made.

Oxymercuration-Demercuration

• Reaction: Alkene reacts with 1) Hg(OAc)₂, H₂O and 2) NaBH₄.
• Product: Alcohol
• Regioselectivity: Markovnikov
• Stereospecificity: Anti
• Enantiomer products may also form.

Modified Oxymercuration-Demercuration (Ether Formation)

• Reaction: Alkene reacts with 1) Hg(OAc)₂, EtOH and 2) NaBH₄.
• Product: Ether
• Regioselectivity: Markovnikov
• Stereospecificity: Anti

Hydrolysis of Epoxide

• Reaction: Epoxide reacts with H₃O⁺.
• Product: Trans-diol.
• Regioselectivity: Occurs under acidic conditions.
• Stereospecificity: Trans.

Syn Addition Reactions

• Syn addition reactions add groups to a double bond on the same side.

Catalytic Hydrogenation

• Reaction: Addition of H to double bonds in syn. Not arene rings.
• Reaction: Alkene reacts with H₂.
• Product: Alkane
• Regioselectivity: Not applicable (N/A).
• Stereospecificity: Syn.

Hydroboration-Oxidation

• Reaction: Alkene reacts with 1) BH₃, THF and 2) H₂O₂,-OH.
• Product: Alcohol, added to the least substituted side
• Regioselectivity: Anti-Markovnikov.
• Stereospecificity: Syn.

Peroxyacid Epoxidation

• Reaction: Forms Epoxide -- 3-member ring with oxygen.
• Product: Epoxide
• Regioselectivity: N/A
• Stereospecificity: Syn

Halohydrin Epoxidation

• Reaction: Forms Epoxide with halogen & strong base.
• Reagents: 1. Cl₂, H₂O, or 2. NaOH
• Byproduct: H₂O + NaCl (if using NaOH)
• Product: Epoxide
• Regloselectivity: N/A
• Stereospecificity: Syn

Hydroxylation (Osmylation)

• Reaction: Alkene to Syn-diols
• Product: Syn diol
• Regioselectivity: N/A
• Stereospecificity: Syn
• Reagents: 1. OsO₄, Pyr 2. NaHSO₃, H₂O

Dichlorocarbene Addition

• Product: Dichloro cyclopropane
• Regioselectivity: N/A.
• Stereospecificity: Syn.
• Attacks a carbene (:CCl₂) to an alkene.

Simmons-Smith Reaction

• Reaction: Cyclopropane formation
• Reagents: CH₂I₂, ZN(Cu), ether
• Product: cyclopropane
• Regioselectivity: N/A
• Stereospecificity: Syn

Simmons-Smith Extension

• Details of the mechanism aren't needed, except how to get to carbenoid (ICH₂-ZnI).
• Carbenoid acts as :CH₂.
• (CH₂I₂ + Zn(Cu) --- ICH₂-ZnI(Carbenoid)

Oxidative Cleavage of Alkenes

• Splits the double bond in two.

Reductive Ozonolysis

• Reaction: Split the double bond, to form a carbonyl group
• Reagents: 1. O₃ 2. Zn, or H+ DMS
• Product; Carbonyl
• Regioselectivity: N/A
• Stereospecificity: N/A
• If 0 H = Ketone
• If 1 H = Aldehyde
• If 2H = Formaldehyde.

Oxidative Cleavage

• Reactions: Forms Carbonyl Groups
• Product:
• KHnO₄, H₃O⁺ --Ketone : OH
• Carboxylic Acid or -: IH
• CO₂ : 2H
• Regioselectivity = N/A
• Stereospecificity = N/A

Oxidative Cleavage of the Diol

• Product - Form carbonyl Groups from the Diol Reagents: HIO₄ , H₂O, THF
• If OH = Ketone
• IH= Aldehyde
• 2H= Formaldehyde Requires to know the intermediate

Alkyne Reactions (Chapter 9)

• Focuses on reactions involving triple bonds

Alkyne Formation

• Reaction: Turns double bond to to triple bond
• Reagents: 1. Br₂, Cl₂Cl₂ 2. 2 eq. KOH
• Product: Alkyne
• Regioselectivity: N/A
• Stereospecificity: N/A

Hydrohalogenation

• Reaction: Addition of 1 or 2 halogens, two diff. products possible
• Reg: HX, ether
  • X or H = Cl/BT
• Products: 1 eq = vinyl halide

1 eq - Mark

• Stereospe: Anti

• Transition State that share the H to avoid #

• 2 eq = same as above , continue with vinyl halide = germinal dihalide

Halogenation

• Reaction: Additions of 2 to 4 halogens.
• Leg: -
• Product of vicinal and dihalide

** Alcohol Addition to the Alkyne**

• Results in enol formation; this undergoes Tautomerization, which converts an enol into Ketone or Aldehyde.

** Acid -Catalyzed Tautomerization**

• reaction: converts in enol into a ketone/ Aldehyde
• Regioselevtivity: N/A
• Stereospecificity: N/A

Addition of an Alcohol to an Internal Alkyne

• Reaction: H₂O, H₂SO₄ or H₂SO₄

Mercury Catalyzed Hydration: needs catalyst

• R: H₂O, H₂SO₄ , HgSO₄
• Regioselectivity: Mark
• Stereospecficity: N/A

Hydroboration-Oxidation (Alkyne)

• Don't need to know Mechanism
• Regioselectivity: Anti-Mark
• Stereospecificity: N/A

Reduction of Alkynes: Can go from triple bond to double or triple to single bond.

Catalytic Hydrogenation - Alkyne to an Alkane

• Regiospecificity: Anti Stereoselevtivity: N/A Palc

DISSOLVING METAL REDUCTION

• Product: Alkene
• Reagents: Na, NH₂ (1) Regiospecificity: N/A
• Stereoselectivity" Trans only internal alkynes , not terminal

Lindlars Reduction: produces cis-alkene

• Reagents: Lindlars catalyst.
• Products: cis- alkane Oxidation + Chain Extension Alkynes : Cut/ Add/ attach to the chain.

31. Oxidative Ozonolysis

• Reagents:

1. O₃, (-78 *degree C)

• Products: 0 Terminal Hydrogen: Carboxylic Acia Terminal Hydrogen = CO₂

32. Acetylide Alkylation: Chain extention.

• Reagents:: 1. Na NH₂ , NH₃ (1), Br