Cu
I
-catalyzed cycloaddition
(CA) of the ketonitrones,
Ph
2
C=N
+
(R′)O
–
(R′ = Me, CH
2
Ph), to the disubstituted cyanamides,
NCNR
2
(R = Me
2
, Et
2
, (CH
2
)
4
, (CH
2
)
5
, (CH
2
)
4
O, C
9
H
10
, (CH
2
Ph)
2
, Ph(Me)), gives the corresponding 5-amino-substituted 2,3-dihydro-1,2,4-oxadiazoles
(15 examples) in good to moderate yields. The reaction proceeds under
mild conditions (CH
2
Cl
2
, RT or 45 °C) and
requires 10 mol % of [Cu(NCMe)
4
](BF
4
) as the
catalyst. The somewhat reduced yields are due to the individual properties
of 2,3-dihydro-1,2,4-oxadiazoles, which easily undergo ring opening
via N—O bond splitting. Results of density functional theory
calculations reveal that the CA of ketonitrones to Cu
I
-bound
cyanamides is a concerted process, and the copper-catalyzed reaction
is controlled by the predominant contribution of the HOMO
dipole
–LUMO
dipolarophile
interaction (group I by Sustmann’s
classification). The metal-involving process is much more asynchronous
and profitable from both kinetic and thermodynamic viewpoints than
the hypothetical metal-free reaction.