Organic Pedagogical Electronic Network Stereoselectivity in Wittig Reactions Created by Jonathan Greenhalgh Edited by Margaret Hilton Honors Organic Chemistry.

Slides:

Advertisements

Similar presentations

WWU -- Chemistry How Do You Hydrate a Double Bond? The problem with this approach is that yields are low, and carbocation rearrangements can complicate.

Advertisements

Elimination Reactions

Elimination Reactions

Elimination Reactions In addition to substitution, alkyl halides can also undergo elimination reactions, which lead to the formation of alkenes. As with.

Chapter 8 Lecture Outline

Prepared by : Malak Eshtayah

Alkyl Halides and Elimination Reactions

Elimination Reactions

The Wittig reaction involves phosphorus ylides as the nucleophilic carbon species. The Wittig and Related Reactions of Phosphorus Stabilized Carbon Nucleophiles.

Identifying Nucleophiles and Electrophiles (a). Identifying Nucleophiles and Electrophiles (b)

Organic Chemistry 4 th Edition Paula Yurkanis Bruice Chapter 18 Carbonyl Compounds II Radicals Irene Lee Case Western Reserve University Cleveland, OH.

1 Chapter 18 Chapter 18 Additions to the Carbonyl Groups Addition to the carbonyl group also occurs at the carbon of a carbonyl groups which is also electrophilic.

CHEMISTRY 4000 Topic #3: Skeleton Oriented Bond-Sets Fall 2012 Dr. Susan Findlay.

© 2014 Pearson Education, Inc. Alkenes Structure, Nomenclature, and an introduction to Reactivity Thermodynamics and Kinetics Chapter 5 Paula Yurkanis.

© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 18 Carbonyl Compounds II Reactions of Aldehydes and Ketones.

Chapter 41 Alkenes. Chapter 4. Chapter 42 Contents of Chapter 3 General Formulae and Nomenclature of Alkenes General Formulae and Nomenclature of Alkenes.

The Nature of Organic Reactions: Alkenes and Alkynes

What makes the carbonyl carbon electrophilic? 1.RESONANCE: What would the resonance hybrid look like? 2.INDUCTION: The carbonyl carbon is bonded to a very.

Nitrogen Based Carbonyl Reactions. Some reactions of aldehydes and ketones progress beyond the nucleophilic addition stage Acetal formation Imines Compounds.

Dr. Wolf's CHM 201 & Molecules with Multiple Chirality Centers.

7.13 Chemical Reactions That Produce Diastereomers

© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 6 The Reactions of Alkynes An Introduction to Multistep.

1 Chapter 13 Silicon reagents  General features  Two other highly important properties of silicon  Reactions of organosilanes  1,2 rearrangements (Brook.

ALKENE AND ALKYNE REACTIONS and SYNTHESIS Dr. Sheppard CHEM 2412 Summer 2015 Klein (2 nd ed.) sections 11.7, 9.1, 9.3, 11.10, , 9.8, 9.7, 14.8,

Chapter 14 Conjugated Compounds and Ultraviolet Spectroscopy.

7 7-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown.

Physical Organic Chemistry CH-4 Nucleophilic aromatic substitution & Elimination reactions Prepared By Dr. Khalid Ahmad Shadid Islamic University in Madinah.

© 2011 Pearson Education, Inc. Chapter 9 Elimination Reactions of Alkyl Halides Competition Between Substitution and Elimination Organic Chemistry 6 th.

Conjugation in Alkadienes and Allylic Systems. A double bond can act like a substituent and give other groups special properties and reactivity. For example.

Alkenes, Alkynes. Required background: Thermodynamics from general chemistry Hybridization Molecular geometry Curved arrow notation Acidity and basicity.

Aldehydes & Ketones: Part II

WWU Chemistry ADDITION-ELIMINATION: NITROGEN AND PHOSPHORUS NUCLEOPHILES Sections

© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 18 Carbonyl Compounds II Reactions of Aldehydes and Ketones.

Chapter 12 Phosphorus reagents Topics: –For conventional Wittig reaction and developed Wittig reaction. –For conversion of hydroxy into halogen.

Alkenes and Alkynes 1 Properties and Synthesis. Elimination Reactions of Alkyl Halides.

Synthesis Biosynthesis Reagents = small carbon-based molecules (e.g. amino acids, carbohydrates) Catalysts = enzymes, proteins that bind and then catalyze.

Organic Pedagogical Electronic Network Solvent Effects Laura Beuth, Jenni Frosch & Hilke Wiedenroth.

Reactions of Alkenes and Alkynes

Organic Pedagogical Electronic Network Properties of Hydrogen Bonding Created by Max Taggart Edited by Margaret Hilton Honors Organic Chemistry Chem 2321.

Redox Relay Heck Reaction

Physical and Chemical Properties and Reactions of Alkenes and Alkynes CHAPTER SEVEN TERRENCE P. SHERLOCK BURLINGTON COUNTY COLLEGE 2004 CHE-240 Unit 3.

Chapter 17 Aldehydes and Ketones II. Aldol Reactions

Biological Chemistry FIRST YEAR ORGANIC CHEMISTRY Lecture Seven Aldehydes & Ketones Convenor : Dr. Fawaz Aldabbagh.

Reduction of Aldehydes and Ketones Complete reduction of a carbonyl group to a methylene (-CH 2 -) group is possible by two different methods 1)Wolff-Kishner.

Preparation of Alkanes Methane through -pentane and iso-pentane can be obtained in pure form by fractional distillation of petroleum and natural gas; neo-pentane.

Organic Chemistry M. R. Naimi-Jamal Faculty of Chemistry Iran University of Science & Technology.

Chapter 18 Additions to the Carbonyl Group Reactions of Aldehydes and Ketones.

Class II Carbonyl Compounds Naturally occurring aldehydes and ketones.

Radical Reactions in Biological Systems

Unit 4 organic chemistry

8.1 Introduction to Elimination

COX 2 Inhibitor Interactions

Redox Relay Heck Reaction

Knoevenagal reaction.

Chemistry Organic Chemistry I Fall, 2014 Day 14 10/3/14

Electrophilic Addition Reactions: Alkenes

Klein, Organic Chemistry 1e

Alkenes CnH2n sp2 hybridized carbons s p p sp2 H H C C H H.

Carbon–carbon bond formation with enols/enolates

Alkenes CnH2n sp2 hybridized carbons s p p sp2 H H C C H H.

Wittig reaction and Allylic Bromination

Conjugated Systems CHEM 2425 Chapter 14.

UNIT SEVEN KEY TOPICS CHAPTER 18

Metabolism of Anabolic Androgenic Steroids

Zimmerman-Traxler Model

Synthesis and Properties of Alkene

Mumbai University (Sybsc) .organic chemistry (USCH301) (SEM III )

CHE 242 UNIT SIX Key Topics: Chapter 15 1,2 vs, 1,4 addition 1

Carbonyl Compounds II Chapter 18.

Presentation transcript:

Organic Pedagogical Electronic Network Stereoselectivity in Wittig Reactions Created by Jonathan Greenhalgh Edited by Margaret Hilton Honors Organic Chemistry Chem 2321 (Sigman), 2013

Stereoselectivity of Wittig Reactions Wiki Page: Overview: The reaction of phosphonium ylides and carbonyls to form alkenes was discovered by Georg Wittig in He received a Nobel Prize in Chemistry for his discovery in Wittig reactions are widely used in organic synthesis because of their ability to selectively create E (trans) or Z (cis) alkenes. Early Examples General Mechanism Georg Wittig 1954 The carbon in the ylide acts as the nucleophile, attacking the carbonyl. This first step forms a C-C bond. The bonds rotate so that the oxygen nucleophile can attack the phosphorus. Then, the P-C bond and C-O bonds break, forming C=C and P=O bonds Horner-Wadsworth-Emmons Reaction 1958 Stephen Martin and Christian Harcken 2001 Other References: Martin, et. al. Org Lett., 2001, 3 (22), 3591Martin, et. al. Org Lett., 2001, 3 (22), 3591 Hodgson, et. al. Org. Lett., 2010, 12 (18), 4204

Destabilized Ylides and Z-Alkenes Wiki Page: Destabilized ylides react with carbonyls to form Z (cis) alkenes Destabilized ylides have no electron withdrawing groups (EWG) attached to the carbon chain The Z in Z-alkene stands for the German word “Zusammen” which means “together” The Z (cis) product is the kinetic product so these reactions are under kinetic control

Stabilized Ylides and E-Alkenes Wiki Page: Stabilized ylides react with carbonyls to form E (trans) alkenes E stands for the German word “Entigen” which means “opposite” Equilibration to the most stable intermediate occurs due to the electron withdrawing group on the carbon chain The equilibrium favors the thermodynamic product, which is the E (trans) alkene Steric hindrance and other factors can alter the E:Z ratio of a reaction

Examples Hong, et. al. Org. Lett. 2009, 11 (22), In 2009, experiments using Wittig and Michael reactions were used to successfully obtain high selectivity of all-cis molecules, as shown above. This is possible in part due to the stereo-specificity of the Wittig reactions used. The above reaction, another variation of the Wittig Reaction, gave 99% enantiomeric excess and a 90% yield.

Problems Reference s : 1aMartin, et. al. Org Lett., 2001, 3 (22), 3592Martin, et. al. Org Lett., 2001, 3 (22), b Martin, et. al. Org Lett., 2001, 3 (22), 3592Martin, et. al. Org Lett., 2001, 3 (22), c Hodgson, et. al. Org. Lett., 2010, 12 (18), 4205Hodgson, et. al. Org. Lett., 2010, 12 (18), Provide mechanisms for the following reactions: a. b. c. 2. Predict the product of the reaction: 3. Predict the structure of intermediate A, the product of the Wittig Reaction of 1 with 2, prior to the Michael reaction. Indicate stereochemistry of the product(s) Hodgson, et. al. Org. Lett., 2010, 12 (18), 4205Hodgson, et. al. Org. Lett., 2010, 12 (18), Hong, et. al. Org. Lett. 2009, 11 (22), Hong, et. al. Org. Lett. 2009, 11 (22),