Diels-Alder Reaction
CHa=CH—CH=CHa • CHa—CH—CH=CH, (XXXIII)
CHa—CH-^CH=^CHa
H
X
CH,—CH=CH—CHa
H
(XXXIV)
H
Br
I
CHa—CH—CH=CH 2 (XXXVa)
I
H
Br° \:2-addition
*•
Br
I
CH,—CH=CH—CH 8 (XXXV6)
I
H
l:4-addition
to occur preferentially at lower temperatures in non-polar solvents
and 1:4-addition at higher temperatures in polar solvents; the temper
ature effect is due to the fact that the activation energy for 1:4-addi
tion is usually higher than that for 1:2-addition (cf. p. 203).
For addition to an unsymmetrical diene the same considerations
apply as in the case of mono-alkenes, thus:
Me-CH=CH-CH=CHa Me— CH==CH*-CH-CH, -* products
H
Me Me
[, -+ CH,
H
=CH, -»• products
(ii) Diels-Alder reaction
The classic example is with butadiene and maleic anhydride
'^6
o
o
A
O