Chapter 16 Discussion

Synthesis problem

Conjugation

How to prepare dienes?

How to prepare dienes?

Retrosynthetic analysis

Retrosynthetic analysis

Synthesis plan

Reactions of conjugated dienes

1,2- and 1,4 addition of HX and X2

Polymerization

Diels Alder cycloaddition

Addition of HX to dienes

kinetic

thermodynamic

Addition of X2 to dienes

kinetic

thermodynamic

Diels-Alder Cycloadditions: one-step preparation of cyclohexenes

?

1) Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right)

2) Draw a cyclohexene ring

3) Build models of the possible isomers that could result from the cycloaddition

4) Use resonance to help predict regioisomer

5) Temperature for endo/exo preference.

1) Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right)

2) Draw a cyclohexene ring

3) Build models of the possible isomers that could result from the cycloaddition

4) Use resonance to help predict regioisomer

5) Temperature for endo/exo preference.

diene dienophile

3) Build models of the possible isomers that could result from the cycloaddition4) Use resonance to help predict regioisomer

5) Temperature for endo/exo preference.

endo

exo

Endo and exo

+ enantiomer + enantiomer

Exo (thermodynamic product)

Endo (kinetic product)

?

1) Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right)

2) Draw a cyclohexene ring

3) Build models of the possible isomers that could result from the cycloaddition

4) Use resonance to help predict regioisomer

5) Temperature for endo/exo preference.

Four possible regioisomers and diastereomers (+ enantiomers)

Resonance contributors show which regioisomers will form

Regiochemistry is established. How about endo or exo?

Problem:Diels-Alder Reactants?