Organic ChemistryELEVENTH EDITION

Chapter 13Conjugated Unsaturated Systems

Solomons • Fryhle • Snyder

Copyright © 2014 by John Wiley & Sons, Inc. All rights reserved.

1,6 addition of Br2 to 1,3,5-cyclooctatriene

Top products are kinetic, bottom are thermodynamic

Degree of substitution of product double bond determines thermodynamic stability

Diels-Alder Reaction

Forward Diels-Alder Reaction

Retrosynthetic Analysis of Diels-Alder Product

• Retrosynthetic analysis involves three steps• First redraw the product with pencil and make the notations shown in left structure

above• Step 1: project double bond to opposite side of 6-membered ring (erase & redraw)• Step 2: erase bonds bonds in 6-membered ring attached to new double bond carbons• Step 3: double bonds in 6-membered ring attached to original double bond carbons

Stereochemistry of Diels-Alder Reaction

• This is so difficult to see that even molecular models don’t help

• To understand this it is necessary to do a careful topology analysis using Newman projections (next slide)

• X1:Y2 = axial:axial trans (anti)• X2:Y1 = equatorial:equatorial trans (gauche)• X1:X2 = axial:equatorial cis (gauche)• Y1:Y2 = equatorial:axial cis (gauche)• X2:ring = equatorial:equatorial (anti)• Y1:ring = equatorial:equatorial (anti)• Y1 and Y2 are leftmost groups in the reactants; wind up cis to one another• X1 and X2 are rightmost groups in the reactants; wind up cis to one another and trans to Y1, Y2

Start with X1 and Y2 which have to be trans because they are anti in the Newman projections

Stereochemical Relationships in Diels-Alder Product Groups