The Sanderson Group Webpages
Department of Chemistry
Durham University, Durham, UK
Organic Chemistry 2 Part C - Eliminations and Cycloadditions
Dr J M Sanderson, Ext 42107, Room 112.
See http://duo.dur.ac.uk for further information.
Aims
These lectures are goven to provide knowledge of 1,2-elimination reactions for making alkenic and alkynic bonds and the involvement of alkenes and alkynes in cycloaddition reactions.
Learning Outcomes
By the end of these lectures, students should be able to:
- Define the terms E1, E1cb and E2.
- Write curly arrow mechanisms to explain the differences between E1, E1cb and E2 eliminations, including the formation of anionic or cationic intermediates.
- Describe how E1 and E2 may be distnguished in terms of reaction kinetics.
- Given an appropriate starting material, predict the thermodynamic product when multiple elimination pathways are possible (i.e. there are two or more β-hydrogens), accounting for the stereo- and regiochemistry observed.
- Account for the formation of Hofmann and Saytzeff products in E2 processes.
- Account for the ratio of substitution to elimination products in terms of steric effects.
- Account for the regio- and stereoselectivity observed in eliminations from cyclic cystems in terms of the steric relationship between the groups eliminated.
- Provide at least three methods for the preparation of benzynes.
- Write a mechanism for the cine-substitution of halobenzenes.
- Write a curly arrow mechanism for the reaction between a diene such as butadiene and dienophile such as maleic anhydride.
- Explain, with the aid of a diagram, orbital overlap between the diene and dienophile in the Diels-Alder reaction.
- Describe the key features of dienes and dienophiles that enable the Diels-Alder reaction to occur, in terms of electronic and conformational factors.
- Predict the stereochemistry (endo vs exo) of the products formed by Diels-Alder reactions.
- Provide a rationale for the reactivity of dienes and dienophiles and the stereochemistry of the cycloadducts in terms of frontier molecular orbital descriptions of the molecules.
- Describe 2π+2π and 4π+2π thermal and photochemical cycloadditions in terms of frontier molecular orbital theory in order to justify whether they are allowed or forbidden.
Lectures
Lecture 1: Introduction. E1 elimination.
Lecture 2: E1 elimination (contd.) and E1cb eliminations.
Lecture 3: E2 eliminations.
Lecture 4: E2 eliminations (contd.) and eliminations from diasteroisomers and cyclic systems.
Lecture 5: Alkyne formation. Benzynes. Introduction to cycloadditions.
Lecture 6: Frontier molecular orbital descriptions of thermal and photochemical cycloadditions.
Reading List
General Texts:
1. J. Clayden, N. Greeves, S. Warren and P. Wothers, “Organic Chemistry”, Oxford University Press, 2000.3. F. A. Carey and R. J. Sundberg, “Advanced Organic Chemistry Parts A & B”, Springer, 5th ed., 2007.