Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

52 NITRILE OXIDES
derivatives 4-R 2 C6H4CNO (R 2 = Me, Cl) to give good yields of dihydrooxadiazolodiazepines
159 (R = Me, R 1 = H, R 2 = H, Me, Cl; R = R 2 = H, R 1 = Me).
The crystal structure of 159 (R = Me, R 1 = H, R 2 = Cl) has also been reported
(325).
MeO
R
N N
MeO
R 1 N
158 159
R
R 1
O
N N
Reactions of 2,3-dihydro-1H -1,4-diazepines with mesitonitrile oxide proceed
with site- and regiospeciÞc 1,3-dipolar cycloaddition leading to bis[1,2,4]
oxadiazolo[1,4]diazepine derivatives 160 (326). Of the three compounds 160 only
the one with R = R ′ = Ph is formed with trans arranged substituents. The two
other products (R = R ′ = Me and R = Me, R ′ = Ph) are mixtures of diastereoisomers.
The heterotricyclic 6,10a,11,11a-tetrahydro-5H -bis[1,2,4]oxadiazolo[4,5d:5
′ ,4 ′ -g][1,4]diazepine structure 160 of the obtained bis-adducts indicates that
the hetero double bonds are much more reactive than the oleÞnic ones. No evidence
for the formation of monoadducts was obtained.
Bis[1,2,4]oxadiazolino[4,5-b;5 ′ ,4 ′ -g][1,2]diazepines 161 (R = mesityl, CF3)
were prepared by a one-step cycloaddition of mesitonitrile and trißuoroacetonitrile
oxides, with 5,7-dimethyl-4H -(or 2H )-1,2-diazepines (327).
R R′
O O
N
N
N N
Mes Mes
160
Me
N
N
O N
161
R 2
O N
Reactions of 1,2-diazepines with nitrile oxides are sometimes difÞcult to
elucidate because they give mixtures (328) or unexpected products. Thus, reactions
of 3-methyl- and 3,7-dimethyl-1,2-diazepines with mesitonitrile oxide leads
to 5,10-dioxa-1,2,4,11-tetrazatricyclo[7,3,1,0 2,6 ]trideca-3,7,11-triene derivatives
162 (R = H, Me, respectively) (329). Such structures were determined by X-ray
diffraction studies (330).
Me
R
R