Mendeleev Commun., 2002, 12(5), 202–203
Allylboration of nitrosobenzene
Yurii N. Bubnov,* Dmitrii G. Pershin, Anna L. Karionova and Mikhail E. Gurskii
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
1
0.1070/MC2002v012n05ABEH001640
The allylboration of nitrosobenzene at –70 °C resulted in the formation of N- and O-allyl derivatives of N-phenylhydrazine, which
were reduced with the second allylborane molecule to N-allylaniline above 100 °C.
The heating of nitrosoarenes with trialkylboranes afforded cor-
responding anilines in low yields; the products of reductive
R
B
R
R
1
–3
alkylation were not detected. The reactions of nitroaromatic
substrates with allylboranes occurred at 80–100 °C and resulted
THF
70 °C
O
N
–
O
N
O
TEA
4
in substituted N-allylanilines and N,N-diallylanilines. The allyl-
HN
boration of nitroso compounds was not studied previously.
We found that nitrosobenzene 1 reacts with triallylborane and
tricrotylborane at –70 °C to form two products of 1,2-addition
at the N=O bond 2 and 4 in a ratio of 3:2 (according to NMR
PhN
O
Ph
Ph
B
Ph
1
2
a,b
3a R = H, 40%
b R = Me, 34%
3
R
3B
data). The deboration of them afforded O- and N-allylated
phenylhydroxylamines 3 and 5, respectively.† Thus, we de-
R
B
R
R
Ph
tected the initially formed allylboration products in contrast to
Ph
Ph
N
O
N
O
N
4
TEA
analogous reactions of triallylborane with nitro compounds. In
THF
70 °C
this case, it is surprising that predominant reaction product 2a
results from the addition of an allyl group and a boron atom at
the oxygen and nitrogen atoms of the N=O bond, respectively.
The low regioselectivity of nitroso group allylboration is of
particular interest. It is well known that all of the previously
studied reactions of allylborane addition to compounds with
polarised multiple bonds are completely regiospecific with no
exception.
OH
–
B
TEA = N(CH CH OH)
3
4a,b
:4 = 3:2
5a R = H, 22%
5b R = Me, 22%
2
2
2
allylboration of an aromatic nitroso group occurred completely
with the allyl rearrangement via a six-membered transition state
(as in all other allylboration reactions). At the same time, the
reasons for the low regioselectivity of this reaction remain
unclear.
O-Allyl- and N-allyl-N-phenylhydroxylamine derivatives 2a
and 4a react with the second mole of triallylborane (100–
10 °C) with the formation of N-allylaniline 6a, diallyl 7 and
Tricrotylborane with nitrosobenzene gives compounds 3b
and 5b, which contain α-methylallyl groups. Thus, the reductive
†
General procedure for nitrosobenzene allylboration. Synthesis of N-
and O-allyl derivatives of N-phenylhydroxylamine 3 and 5. A solution of
3
5
0 mmol of nitrosobenzene in 150 cm of THF was added dropwise to a
1
3
solution of 50 mmol R B (R = All, Crt) in 75 cm of THF at –65 °C with
3
allyl alcohol 8.
continuously stirring. The mixture was heated to 20 °C and stirred for
3
2
h. After deboration with triethanolamine (46.6 mmol in 20 cm of THF),
the mixture of products 3 and 5 was separated by column chromato-
3B
3B
100–110 °C
TEA
graphy on SiO (hexane–diethyl ether, 10:1).
2
Ph
N
O
2a + 4a
–
70 °C
20 °C
O-Allyl-N-phenylhydroxylamine 3a: yellow oil, 2.8 g (40%) yield,
bp 49–52 °C (0.01 Torr). n1 = 1.5395. H NMR (CDCl ) d: 4.5 (d, 2H,
8
1
1
D
3
OCH , J 6.2 Hz), 5.3–5.5 (m, 2H, =CH ), 5.9–6.25 (m, 1H, CH=), 6.9
2
2
OH
8, ~70%
(
2
1
d, 2H, o-H, J 8.8 Hz), 7.05 (m, 1H, p-H), 7.2 (br. s, 1H, NH), 7.25 (m,
Ph NH
1
3
H, m-H). C NMR (CDCl ) d: 75.8 (O–C), 114.2 (o-C), 118.6 (p-C),
3
21.7 (=CH ), 128.8 (m-C), 133.4 (CH=), 148.35 (i-C). MS, m/z: 149
6a, 70%
7, ~30%
2
+
[
M] . Found (%): C, 72.44; H, 7.37. Calc. for C H NO (%): C, 72.45;
9
11
H, 7.43.
The reduction of intermediate products 2 and 4 was found to
occur via completely different mechanisms.
N-Allyl-N-phenylhydroxylamine 5a: yellow oil, 1.54 g (22%) yield.
H NMR (CDCl ) d: 4.05 (d, 2H, NCH , J 5.4 Hz), 5.3–5.5 (m, 2H,
1
3
2
The action of triallylborane on compound 5a (1:1) resulted
in practically pure derivative 4a. The heating of the latter with
an additional mole of triallylborane and the subsequent debora-
tion resulted in N-allylaniline 6a and diallyl 7. Compound 5b
reacted analogously to give N-(1-methylallyl)aniline 6b and
diallyl 7. In this case, the redox process associated with N–O
bond cleavage was accompanied by the generation of allyl
radicals, the recombination of which afforded diallyl. The for-
mation of radical combination products such as biphenyl in
=
CH ), 5.9–6.2 (m, 1H, CH=), 6.9 (br. s, OH), 7.05 (m, 2H, m-H), 7.2
2
1
3
(d, 2H, o-H, J 7.7 Hz), 7.35 (m, 1H, p-H). C NMR (CDCl ) d: 62.4
3
(
1
N–C), 116.9 (o-C), 118.9 (=CH ), 122.4 (p-C), 128.6 (m-C), 133.1 (CH=),
52.1 (i-C). MS, m/z: 149 [M] . Found (%): C, 72.48; H, 7.38. Calc. for
2
+
C H NO (%): C, 72.45; H, 7.43.
9
11
O-(1-Methylprop-2-en-1-yl)-N-phenylhydroxylamine 3b: 2.6 g (34%)
yield, bp 82–84 °C (0.01 Torr). n1 = 1.5275. H NMR (CDCl ) d: 1.45
8
1
D
3
(
d, 2H, Me, J 7.2 Hz), 4.4 (m, 1H, OCH), 5.25–5.4 (m, 2H, =CH ), 5.9–
.1 (m, 1H, CH=), 6.9 (s, NH) 7.0–7.1 (m, 3H, o-H, p-H), 7.3–7.4 (m,
H, m-H). C NMR (CDCl ) d: 19.4 (Me), 80.6 (O–C), 114.4 (o-C),
17.4 (p-C), 121.85 (=CH ), 129.1 (m-C), 139.1 (CH=), 148.8 (i-C).
2
6
2
1
1
3
the reaction of arylmagnesium compounds with hydroxylamine
3
derivatives is well known.5
2
+
MS, m/z: 163 [M] . Found (%): C, 73.87; H, 8.23. Calc. for C H NO
1
0
13
At the same time, the formation of N-allylaniline from com-
pound 3a formally is the replacement of the O-allyl group by
an allyl group. It is interesting in the test reaction that the
entering allyl group retains its configuration; that is, the reac-
tion of O-allyl derivatives with allylboranes occurs with no allyl
rearrangement. This was found in the action of tricrotylborane
on O-allyl derivatives 2.
(
%): C, 73.58; H, 8.03.
N-(1-Methylprop-2-en-1-yl)-N-phenylhydroxylamine 5b: 1.7 g (22%)
yield, bp 92–95 °C (0.01 Torr). n1 = 1.5422. H NMR (CDCl ) d: 1.35
8
1
D
3
(
=
d, 3H, Me, J 16.4 Hz), 4.1–4.25 (m, 1H, NCH), 5.05–5.2 (m, 2H,
CH ), 6.0–6.1 (m, 1H, CH=), 7.0 (br. s, 1H, OH), 7.4–7.6 (m, 5H,
2
1
3
aromatic protons). C NMR (CDCl ) d: 15.7 (Me), 65.0 (N–C), 116.7
3
(
(
=CH ), 118.5 (o-C), 122.8 (p-C), 128.6 (m-C), 138.0 (CH=), 151.5
i-C). MS, m/z: 163 [M] . Found (%): C, 73.55; H, 8.05. Calc. for
2
+
A few allylborane reactions that occur by the direct cleavage
of the boron–carbon bond (with no allyl rearrangement) are
C H NO (%): C, 73.58; H, 8.03.
10
13
–
202 –