Dicls-Aldcr Rcactions of N-Acyl-1,2.4,5-tctrazincs 201
1. The reaction of la with phenyl acetylene yields a mixture of regioisomers 8 and
9 in a product ratio 2:1 (Scheme 30.5).
DATA: Phenyl acetylene: EuoMo -9.5 eV; C-lcoefficient 0.580; C-2 coefficient 0.650.
NHAc
NHAc
NHAc
N~N
140 °C
N~ Nl Ph
11
1
+ Ph :=:
11
+ 11
NYN
60 h
N o Ph
N hSCH3
SCH3
SCH3
1a
8
9
(2: 1)
Scheme30.5
2. Formulate the structure of the product obtained after heating compound 10 in
dioxane.
10
Answer to Question 1
It is clear that by using phenyl acetylene as dienophile the reaction is less regioselective than in the case of ethyl vinyl ether (a 2:1 mixture of regioisomers 8 and 9
is obtained in this case). By looking at the C-1 and C-2 coefficients in the HOMO
of the phenyl acetylene we will realize that they ha ve very similar values (Scheme
30.6). As discussed previously, the regioselectivity is governed by the overlapping
between the positions bearing the largest coefficients in the LUMO of the diene
and the HOMO of the dienophile (of course having the same sign). In this case,
the difference between the coefficients ofboth acetylenic carbons is small and this
would be the reason for the lower regioselectivity of the reaction in comparison to
that ofthe dienophiles previously described. Again the major regioisomer 8 would
result from the overlapping between the positions C-6 and C-2 having the largest
coefficients, whilst the minor regioisomer 9 would result trom the interaction between the positions C-6 and C-1.
1. The reaction of la with phenyl acetylene yields a mixture of regioisomers 8 and
9 in a product ratio 2:1 (Scheme 30.5).
DATA: Phenyl acetylene: EuoMo -9.5 eV; C-lcoefficient 0.580; C-2 coefficient 0.650.
NHAc
NHAc
NHAc
N~N
140 °C
N~ Nl Ph
11
1
+ Ph :=:
11
+ 11
NYN
60 h
N o Ph
N hSCH3
SCH3
SCH3
1a
8
9
(2: 1)
Scheme30.5
2. Formulate the structure of the product obtained after heating compound 10 in
dioxane.
10
Answer to Question 1
It is clear that by using phenyl acetylene as dienophile the reaction is less regioselective than in the case of ethyl vinyl ether (a 2:1 mixture of regioisomers 8 and 9
is obtained in this case). By looking at the C-1 and C-2 coefficients in the HOMO
of the phenyl acetylene we will realize that they ha ve very similar values (Scheme
30.6). As discussed previously, the regioselectivity is governed by the overlapping
between the positions bearing the largest coefficients in the LUMO of the diene
and the HOMO of the dienophile (of course having the same sign). In this case,
the difference between the coefficients ofboth acetylenic carbons is small and this
would be the reason for the lower regioselectivity of the reaction in comparison to
that ofthe dienophiles previously described. Again the major regioisomer 8 would
result from the overlapping between the positions C-6 and C-2 having the largest
coefficients, whilst the minor regioisomer 9 would result trom the interaction between the positions C-6 and C-1.