Diels Alder Regioselectivity -...

Unformatted text preview: Diels
Alder
Reac-on
‐
Regioselec-vity
 A
rule
to
remember:
 Diels
Alder
reac-on
is
a
cycloaddi-on
 with
an
aroma-c
transi-on
state
that
 is
ortho
and
para
direc-ng
 X X Z Z X = EDG such as alkyl, aryl, RO, Me3SiO, R2N Z X Z X Z = EWG or conjugating group such as CHO, COR, COOH, COOR, CN, NO2, halogen, alkenyl, aryl How
to
decide
which
product
is
formed?
 •  Draw
an
”ionic”
stepwise
mechanism
for
the
reac-on
to
establish
which
 end
of
the
diene
will
react
with
which
end
of
dienophile.
 –  First
decide
where
the
diene
will
act
as
a
nucleophile
and
where
the
 dienophile
will
act
as
an
electrophile
 CN .. MeO .. E Nu –  Draw
the
reagents
in
the
correct
orienta-on
for
the
two
ends
to
combine
and
 draw
a
concerted
Diels‐Alder
reac-on
 CN MeO CN MeO ...
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