An aza-brook rearrangement of (α-silylallyl)amine

Full text of DOI:10.1021/jo952116x

1196
J . Org. Chem. 1996, 61, 1196-1197
Sch em e 1
An Aza -Br ook Rea r r a n gem en t of
(r-Silyla llyl)a m in e
Takahiro Honda and Miwako Mori*
Faculty of Pharmaceutical Sciences, Hokkaido University,
Sapporo, 060 J apan
Received November 30, 1995
The Brook rearrangement of R-silyl alcohol is useful
in synthetic organic chemistry.1 In this reaction, an
alkoxy anion attacks the silyl group to produce an
R-alkoxy anion, and a new carbon-carbon bond is formed
at the carbon R to the alkoxy group. In the case of
R-silylallyl alcohol, an allyl anion is formed by Brook
rearrangement and the carbon-carbon bond is formed
at the R- or γ-position of the allyl alcohol.2 However,
there are few reports on the Brook-type rearrangement
of R-silylamine.3 We report here a new carbon-carbon
bond formation using an aza-Brook rearrangement
(Scheme 1).
Sch em e 2
We previously reported the synthesis of (R-silylallyl)-
amine 3 from alkyne 1 and η2-iminosilaacyl complex 2,
which was prepared by the insertion of isonitrile 5 into
the silyl-zirconium bond of complex 4, in the presence
of LiEt3BH4 in a one-pot reaction. In this reaction, η2-
iminosilaacyl complex 2 reacts with LiEt3BH to give
azazirconacyclopropane 6, and insertion of alkyne 1 into
the zirconium-carbon bond of 6 occurs to give azazir-
conacyclopentene 7, which is hydrolyzed to produce (R-
silylallyl)amine 3. Using this procedure, (R-silylallyl)-
amines 3a , 3b , and 3c were prepared from the cor-
responding alkynes 1a , 1b, and 1c in good to moderate
yields (Scheme 2).
Sch em e 3
To a THF solution of (R-silylallyl)amine 3a was added
BuLi at -78 °C, and the solution was stirred at the same
temperature for 30 min. To this solution was added MeI
at -78 °C, and the solution was stirred at the same
temperature for 30 min. After the usual workup, the
methylation product 8a , the methyl group of which was
introduced at the carbon γ to the allylamine, was
obtained in 40% yield along with allylsilane 9 in 20%
yield.5 The desired alkylation product 8a was obtained
in a quantitative yield with the addition of HMPA. These
results indicate that an aza-Brook rearrangement occurs;
i.e., the silyl group of (R-silylallyl)amine 3a migrates from
carbon to nitrogen and an allyl anion 10 is produced
(Scheme 3).
Sch em e 4
To confirm the generation of the allyl anion by an aza-
Brook rearrangement, the deuterated (R-silylallyl)amine
3a -d,4 which was prepared from 1a and 2 in the presence
of LiEt3BD, was reacted with BuLi and then treated with
alkyl halide 11b (Scheme 4). After acid hydrolysis, the
deuterated aldehyde 12b-d was obtained in 60% yield (D-
content > 90 %). This means that the deuterium at the
allylic position of 3a -d is not abstracted by BuLi, while
the nitrogen proton is directly abstracted by BuLi to
produce the lithium amide, which attacks the silyl group
on the carbon R to nitrogen to produce N-silylallyl anion
10-d.4 As a result, a carbon-carbon bond is formed at
the carbon γ to the allylamine. Moreover, the results
indicate that two functional groups are introduced to each
alkyne carbon, respectively. One is the formyl group
derived from the η2-iminosilaacyl complex and the other
is an electrophile, which is introduced by aza-Brook
rearrangement (Figure 1).
(1) Brook, A. G. Acc. Chem. Res. 1974, 7, 77.
(2) Yamamoto, Y. Comprehensive Organic Synthesis; Trost, B. M.,
Ed.; Pergamon: Oxford, 1991; Vol. 1, p 55.
(3) For the synthesis of (R-silylalkyl)amine: (a) Okazaki, S.; Sato,
Y. Synthesis 1990, 36. (b) Beak, P.; Kerrick, S. T.; Wu, S.; Chu, J . J .
Am. Chem. Soc. 1994, 116, 3231. (c) Sakuragi, A.; Shirai, N.; Sato,
Y.; Kurono, Y.; Hatano, K. J . Org. Chem. 1994, 59, 148. (d) Labrecque,
D.; Nwe, K. T.; Chan, T. H. Organometallics 1994, 13, 332. (e)
Katritzky, A. R.; Hong, Q.; Yang, Z. Organometallics 1995, 14, 734. (f)
Murai, T.; Oda, T.; Kimura, F.; Onishi, H.; Kanda, T.; Kato, S. J . Chem.
Soc., Chem. Commun. 1994, 2143.
(4) Honda, T.; Satoh, S.; Mori, M. Organometallics 1995, 14, 1548.
(5) Compound 9 was formed by migration of the silyl group from
the nitrogen to the γ carbon of N-(silylallyl)anion 10 and subsequent
N-methylation.
(R-Silylallyl)amine 3a was reacted with various alkyl
halides, and the results are shown in the Table. The
results indicate that the allyl, benzyl, and alkyl halides
can be introduced to the carbon γ to the allylamine 3.
0022-3263/96/1961-1196$12.00/0 © 1996 American Chemical Society

Communications
J . Org. Chem., Vol. 61, No. 4, 1996 1197
Ta ble 1. Rea ction of 3a -c w ith E-X F ollow ed by Acid
Hyd r olysis
product
run
substrate
E-X 11
yield (%)
1
2
3
4
5
6
7
8
3a , R1 ) R2 ) Pr
BnO(CH2)3-I (11b)
12b (67)
12b (59)
3a
BnO(CH2)3-Br (11b′)
3b, R1 ) Ph, R2 ) nC5H11 CH2dCHCH2-Br (11c) 13 (92)
3c, R1 ) nC5H11, R2 ) H BnO(CH2)3-I (11b)
14 (36)a
3a
3a
3a
3a
CH2dCHCH2-Br (11c) 12c (66)
Bn-Br (11d )
12d (51)
12e (59)
12f (57)
Pr-Br (11e)
F igu r e 1.
Ph(CH2)3-Br (11f)
a
The yield of the corresponding alcohol (NaBH4/MeOH).
The alkyl iodide gives slightly better results than the
alkyl bromide, in terms of the yield of the desired product
12 (Table 1, runs 1 and 2).
bonds are formed for each alkyne carbon, respectively.
Further studies are in progress.
In conclusion, an aza-Brook rearrangement of (R-
silylallyl)amine, which was easily prepared from alkyne
and an η2-iminosilaacyl complex in the presence of
LiBEt3H, has been realized. Two new carbon-carbon
Su p p or tin g In for m a tion Ava ila ble: Typical procedure
and compound characterization data (5 pages).
J O952116X