Chemistry Reference
In-Depth Information
TABLE 12.9. Selectivity of Singlet Nitrene Insertion into the Tertiary, Secondary, and
Primary CH Bonds of 2-Methylbutane
160
Reactivity per C
H Bond
Nitrene
Tertiary
Secondary
Primary
(EtO)
2
P(O)N,
1
79a
6.0
4.3
1
(PhO)
2
P(O)N,
1
79b
3.4
1.2
1
EtOC(O)N,
1
49a
34
9
1
tBuOC(O)N,
1
49c
160
9
1
azide (
81a
) in cyclohexane led to the diethyl cyclohexylphosphoramidate (
96a
)in
) in 12% yield.
160
The phosphoramidate
88% yield and diethylphosphoramide (
97a
is a products of the singlet nitrene
1
79a
96a
insertion into the CH bond of the solvent,
is a product of the triplet nitrene (
3
79a
the phosphoramide
97a
) reaction. Surpris-
ingly, no by-products were detected
160
which is not
typical of organic azide
photolysis.
5,6,15
Photolysis of diphenylphosphoryl azide (
81b
) in cyclohexane
gave a 67% yield of the insertion product
96b
along with unidentified products
of side reactions.
160
Relative selectivity of nitrenes
79a,b
toward insertion into the tertiary, secondary,
H bonds was also investigated.
160
Photolysis of azide
and primary C
81a
in
2-methylbutane gave amide
in 7% yield and a mixture of four phosphoramidates
in 74% yield, resulting from insertion into the C
97a
H bonds of the solvent. With azide
81b
, the corresponding insertion products were obtained in 65% yield. The selec-
tivity of nitrenes
as well as carbonyl nitrene
1
3b
and nitrene ester
1
49a
are
given in Table 12.9. The data in Table 12.9 demonstrate that phosphoryl nitrenes are
significantly less selective among the C
79a,b
H bonds than other acyl nitrenes.
Very interesting results were obtained upon photolysis of azide
in
tert
-butyl
alcohol.
160
The insertion of nitrene
1
79a
into both the C
H (35%) and the O
H
(33%) bonds of alcohol was observed.
160
This gives a further evidence of the highly
reactive and unselective nature of the singlet phosphoryl nitrenes.
It was also demonstrated that phosphoryl nitrenes with long-chain alkyl or steroid
substituents do not undergo intramolecular insertion reactions, only products of the
insertion into solvents were detected.
161
No detectable amount of cyclization product
or other products of intramolecular reactions were detected upon photolysis of azide
81c
81a
in cyclohexane, CH
2
Cl
2
, and
tert
-butyl alcohol (Scheme 12.45).
161
O
O
P
CH(CH
3
)
2
(H
3
C)
2
HC
O
N
3
81c
.
161
SCHEME 12.45.
Structure of azide
81c
