Asymmetric [2,3]sigmatropic rearrangement of chiral allylic selenimides

Full text of DOI:10.1021/jo960287b

2932
J . Org. Chem. 1996, 61, 2932-2933
Sch em e 1
Asym m etr ic [2,3]Sigm a tr op ic
Rea r r a n gem en t of Ch ir a l Allylic
Selen im id es
Noriyuki Kurose, Tamiko Takahashi, and
Toru Koizumi*
Faculty of Pharmaceutical Sciences,
Toyama Medical & Pharmaceutical University,
2630 Sugitani, Toyama 930-01, J apan
Received February 13, 1996
In contrast to the many reports on asymmetric reac-
tions using chiral sulfinyl compounds, few applications
of chiral seleninyl compounds to asymmetric synthesis
have been described.1 Recently, some groups have
reported the asymmetric [2,3]sigmatropic rearrangement
of chiral selenoxides.1 Uemura and co-workers have
succeeded in the asymmetric [2,3]sigmatropic rearrange-
ment of chiral selenimides giving the chiral sulfonamide
with up to 87% enantiomeric excess.2 However, the
stereochemical course of the reaction was not described.
The key steps of these asymmetric reactions are enantio-
or diastereoselective oxidation or imination of the se-
lenides and transfer of the chirality of the selenium atom
to C-3 of the resulting allylic alcohols or amines. We
recently reported the first synthesis of optically pure
haloselenuranes using the 2-exo-hydroxy-10-bornyl group
as a chiral ligand.3 Alkaline hydrolysis of the (RSe)-
chloroselenurane proceeds with retention of configuration
to give (RSe)-selenoxide as the sole product.3,4 This
selenoxide is stable at room temperature due to the
bulkiness of the bornyl group as well as in intramolecular
hydrogen bond between the seleninyl oxygen and the
secondary hydroxy group.5 Nucleophilic reaction of the
corresponding chiral allylic chloroselenurane with an
N-protected amine should also occur with complete
retention of configuration. If [2,3]sigmatropic rearrange-
ment of the resulting allylic selenimide proceeded ste-
reoselectively, a chiral N-protected allylic amine would
be obtained with high enantioselectivity. We report here
that the nucleophilic reaction of the allylic chloro-
selenuranes with N-protected amines followed by the
[2,3]sigmatropic rearrangement of the resulting chiral
allylic selenimides proceeds in a highly stereoselective
manner to afford chiral N-protected allylic amines. [2,3]-
Sigmatropic rearrangement of the allylic selenimides was
evidenced to progress selectively via an endo transition
state.
Sch em e 2
verted to the corresponding MOM ether 2. Reaction of
2 with sodium selenolate7 followed by hydrolysis of the
resulting diselenide 3 gave the deprotected diselenide 4.
Allylic selenides 5 and 6 were obtained by reaction of
cinnamyl chloride or allylic mesylate with selenolate
anion which was prepared in situ from 4 and sodium
borohydride.8 Treatment of the allylic selenides 5 and 6
with t-BuOCl gave allylic chloroselenuranes 7 and 8 as
an exclusive product.9 We selected benzyl carbamate,
tert-butyl carbamate, p-tosylamide, and diphenylphos-
phinamide as an N-protected amine for selenimide
formation (Scheme 2 and Table 1). Nucleophilic reaction
of 7 and 8 with lithium N-protected amides afforded
chiral allylic selenimides, 9a -d and 10a -d , in situ, with
retention of configuration. [2,3]Sigmatropic rearrange-
ment of 9a -d and 10a -d gave chiral N-protected allylic
amines 11a -d and 12a -d . These results are shown in
Table 1. The ee values of allylic amines 11 and 12 were
determined by HPLC using a Daicel Chiralcel OJ or a
Chiralpak AS column. Determination of the absolute
configuration of 11 and 12 is summarized in the footnote
of Table 1.
Allylic selenides were prepared by a route shown in
Scheme 1. (1S)-10-Bromo-2-exo-borneol (1)6 was con-
(1) For asymmetric [2,3]sigmatropic rearrangement of chiral
selenoxides: (a) Nishibayashi, Y.; Singh, J . D.; Fukuzawa, S.; Uemura,
S. J . Org. Chem. 1995, 60, 4114. (b) Komatsu, N.; Nishibayashi, Y.;
Uemura, S. Tetrahedron Lett. 1993, 34, 2339. (c) Davis, F. A.; Reddy,
R. T. J . Org. Chem. 1992, 57, 2599. (d) Reich, H. J .; Yelm, K. E. J .
Org. Chem. 1991, 56, 5672. For asymmetric â-elimination of chiral
selenoxides: ref 1a and references cited therein.
(2) Nishibayashi, Y.; Chiba, T.; Ohe, K.; Uemura, S. J . Chem. Soc.,
Chem. Commun. 1995, 59, 3262.
(3) Takahashi, T.; Kurose, N.; Kawanami, S.; Arai, Y.; Koizumi, T.;
Shiro, M. J . Org. Chem. 1994, 59, 3262.
(4) Nucleophilic reaction of the (RSe)-chloroselenurane with active
methylene compounds also proceeds with retention of configuration
to afford (SSe)-selenonium ylides exclusively: Takahashi, T.; Kurose,
N.; Kawanami, S.; Nojiri, A.; Arai, Y.; Koizumi, T.; Shiro, M. Chem.
Lett. 1995, 379.
(5) We have applied this selenoxide to an asymmetric protonation
reaction: Takahashi, T.; Nakao, N.; Koizumi, T. Chem. Lett. 1996, 207.
(6) Poth, N. Rev. Tech. Luxemb. 1976, 68, 195; Chem. Abstr. 1977,
87, 135965k.
(7) Syper, L.; Młochowski, J . Synthesis 1984, 439.
(8) Scaborough, R. M., J r.; Toder, B. H.; Smith, A. B., III. J . Am.
Chem. Soc. 1980, 102, 3904.
(9) The structure of chloroselenuranes was confirmed by comparison
of their 1H-NMR spectra with that of (1S,RSe)-5-chloro-10,10-dimethyl-
5-phenyl-5λ4-selena-4-oxatricyclo[5.2.1.03,7]decane (ref 3).
(10) Moriwake, T.; Hamano, S.; Saito, S.; Torii, S.; Kashino, S. J .
Org. Chem. 1989, 54, 4114.
S0022-3263(96)00287-3 CCC: $12.00 © 1996 American Chemical Society

Communications
J . Org. Chem., Vol. 61, No. 9, 1996 2933
Ta ble 1. Asym m etr ic [2,3]Sigm a tr op ic Rea r r a n gem en t
Sch em e 3
of Selen im id es 9a -d a n d 10a -d
time yield eea
entry
R
R’
product (h)
(%) (%) [R]D confign
1
2
3
4
5
6b
7
8
9
Ph Cbz
i-Pr Cbz
Ph Boc
i-Pr Boc
Ph p-Ts
Ph p-Ts
i-Pr p-Ts
Ph Ph2P(O)
i-Pr Ph2P(O)
11a
12a
11b
12b
11c
11c
12c
11d
12d
3
3
3
3
3
3
3
5
5
67 24 -14.1
57 67 +19.6
74
Se
7c -0.7
63 73d +22.0
57 90 +49.2
74 93 -50.2
86 93 +22.7
53 92 +25.7
69 93 +17.7
Sf
Rg
Sg
Sf
Rg
Sh
a
b
Determined by HPLC. ent-7 was used for the reaction.
c Determined after conversion of 11b into 11c. The ee of 11c was
consistent with that of 11b which was determined by 1H-NMR
sigmatropic rearrangement of the allylic selenimides as
shown in Scheme 3. Nucleophilic reaction of the chloro-
selenuranes 7 and 8 with N-protected amines will form
the selenimides 9 and 10 exclusively. In the [2,3]-
sigmatropic rearrangement of the allylic selenimides, the
endo transition state will be more stable than the exo
transition state similar to that of allylic selenoxides.1 In
the formation of N-p-tosylamides 11c and 12c as well as
N-diphenylphosphinamides 11d and 12d the steric in-
teraction would be increased between the alkyl group and
the p-Ts or Ph2P(O) group in the exo transition state,
leading to high stereoselectivity.
In conclusion, the [2,3]sigmatropic rearrangement of
the allylic selenimides (1) proceeds predominantly via the
endo transition state and (2) is available for practical
preparation of various chiral allylic amines.
We are now investigating mechanistic studies on the
[2,3]sigmatropic rearrangement reaction of the selen-
imides in more detail.
d
spectrum using Eu(hfc)3. Determined after conversion of 12b into
12a . The ee of 12a was consistent with that of 12b which was
determined by HPLC. e Determined by comparison with the
authentic sample by HPLC. f Determined by comparison of the
g
sign of optical rotation with the reported one.10 The absolute
configuration of 11c,d was determined from the steric course of
h
the reaction. Determined after conversion of 12d into 12c.
Treatment of 7 and 8 with 3 equiv of CbzNHLi
(prepared from CbzNH2 and n-BuLi) gave the allylic Cbz-
amines 11a (24% ee) and (S)-12a (67% ee), respectively
(Table 1, entries 1 and 2). Reaction of 7 and 8 with
BocNHLi afforded the allylic Boc-amines 11b (7% ee) and
(S)-12b (73% ee), respectively (Table 1, entries 3 and 4).
Treatment of 7 and 8 with p-TsNHLi yielded the corre-
sponding allylic p-tosylamides (R)-11c11 (90% ee) and (S)-
12c (93% ee) (Table 1, entries 5 and 7). When ent-712
and p-TsNHLi were used for this reaction, the preferred
configuration of 11c changed to S (93% ee) (Table 1, entry
6). The ee of allylic phosphinamides, (R)-11d and (S)-
12d , went up to 92% and 93%, respectively, when 7 and
8 were treated with Ph2P(O)NHLi (Table 1, entries 8 and
9). Thus, we obtained (S)-12c with the highest ee (93%)
and chemical yield (86%) in the rearrangement of selen-
imide 10c.
Ack n ow led gm en t. This work was supported in part
by Grants-in-Aid for Scientific Research from the Min-
istry of Education, Science, Sports and Culture, J apan
No. 07214214 (T.K.), No. 07457519 (T.K.), and No.
07672261 (T.T.), by Hoan Sha Foundation (T.K.), and
by The Tamura Foundation for Promotion of Science
and Technology (T.T.).
From the absolute configuration of the resulting N-
protected allylic amines as well as their high ee, we
propose the stereochemical course of the asymmetric [2,3]-
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures, characterization data, and 1H and 13C NMR spectra
for new compounds (40 pages).
(11) Uemura et al. have obtained 11c in 87% ee. Its absolute
configuration has not been reported (ref 2).
(12) ent-7 was prepared from (1R)-10-camphorsulphonic acid ac-
cording to the method for the synthesis of 7 in 29% overall yield.
J O960287B