Chapter 16: Conjugated Pi Systems and Pericyclic Reactions

A sterically hindered base can be used to form dienes via

elimination reaction

A sterically hindered base can be used to form dienes via

elimination reaction

Two products obtained with a conjugated diene

Cycloaddition reactions

sigmatropic rearrangement

electrocyclic reactions

Diels-Alder reaction; [4+2 cycloaddition

Dienophile needs to possess an electron withdrawing group

or the reaction will require high temp, which does not favor

product formation

When an electron-withdrawing group is attached to the

dienophile, the reaction is generally spontaneous

Diels-Alder reactions are stereospecific depending on whether

an (E) or (Z) dienophile is used

Diels-Alder reactions are stereospecific depending on whether

an (E) or (Z) dienophile is used

An alkyne can also function as a dienophile

Dienes trapped in an s-trans conformation can not undergo

Diels-Alder reaction, because carbons 1 and 4 are too far apar

Dienes that are locked into the s-cis conformation undergo

Diels-Alder reactions readily

Cyclopentadiene is so reactive towards Diels-Alder

reaction that it reacts with itself at room temperature to

form a dimer

Only one regiochemical outcome if the diene or dienophile is

symmetrical

Only one regiochemical outcome if the diene or dienophile is

symmetrical

If diene and dienophile are both unsymmetrical, then two

regioisomeric products are possible

The alignment of the electrostatic forces results in a lower

energy transition state; the major product is formed faster