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

t-Bu
t-Bu
PhC(
NOH)
180
REACTIONS OF NITRILE OXIDES 57
N O
R 1 = H, R 2 = H, Me; R 1 = Me, R 2 = Me, Et; R 1 R 2 = (CH 2) 6
O
O
ArCNO
t-Bu
t-Bu
181
O
O
O
O N
R 1
R 2
Ar
t-Bu
O
t-Bu
Ar Ph 4-MeOC6H 4 3,4-(MeO) 2C 6H 3 4-ClC 6H 4 3-ClC 6H 4 4-MeC 6H 4
181/182 1 : 1 1 : 1 1 : 1 1.6 : 1 2 : 1 3 : 1
Scheme 1.31
A synthesis of novel spirodioxazole systems by the 1,3-dipolar cycloaddition
reactions of 3,5-di-tert-butyl-1,2-benzoquinone with aromatic nitrile oxides has
been described (Scheme 1.31). Though yields are high (80%–100%), the regioselectivity
is low, the regioisomer ratio 181:182 being dependent on the Ar nature
(349).
Mesitonitrile oxide undergoes a reversible cycloaddition to the carbonyl group
of the 1-oxo-3-azoniabutatriene salts RR 1 C=N + =C=O SbCl6 − to give the
2-azoniaallene salts 183. X-ray structural analysis of 183 (R = NMePh, R 1 = H)
confirmed the proposed structure (350). 1-Thia-3-azoniabutatriene salts,
RR 1 C=N + =C=S SbCl6 − (R,R 1 = H, Me2N; Ph, Me2N) react with nitrile oxides
at the C=S double bond to yield 2-azoniaallene salts 184 (351).
RR N
C
O
N
O
Me
1C Me
Me
183
R Me2N, MePhN; R1 ·
SbCl 0
6
Me2N Ph
C
·
N
S
O
N
R
0 SbCl6
184
@ @ H, Ph R @
mesityl, 2,4,6–(MeO)3C6H2
Face selectivity in the 1,3-dipolar cycloaddition reactions of benzonitrile oxide
and its p-substituted derivatives with 5-substituted adamantane-2-thiones,
182
O
O
N
Ar