LETTER
First Allylation of Imines with Allyltrichlorosilanes
1751
Meanwhile, it was also found that introduction of a 4-me-
thyl group on the aromatic ring of 5a, i.e. a 2-amino-p-
cresol derivative, improved the yields of CAN- or
PhI(OAc)2-deprotection to some extent (40–55%), indi-
cating that an interaction (possibly cyclization7) between
the C=C double bond and the aromatic group might be
suppressed by the methyl group under the oxidation
conditions. Thus, deprotection of both syn- and anti-crot-
ylation products 8 derived from 2-amino-p-cresol8 provid-
ed the corresponding syn- and anti-homoallylic primary
amines 99 without epimerization (Scheme 3).
References
(1) For recent reviews on allylmetal additions: (a) Puentes, C.
O.; Kouznetsov, V. J. Heterocycl. Chem. 2002, 39, 595.
(b) Denmark, S. E.; Almstead, N. G. In Modern Carbonyl
Chemistry; Otera, J., Ed.; Wiley-VHC: Weinheim, 2000,
Chap. 10. (c) Chemler, S. R.; Roush, R. W. In Modern
Carbonyl Chemistry; Otera, J., Ed.; Wiley-VHC: Weinheim,
2000, Chap. 11. (d) Kobayashi, S.; Ishitani, H. Chem. Rev.
1999, 99, 1069. (e) Enders, D.; Reinhold, U. Tetrahedron:
Asymmetry 1997, 8, 1895. (f) Yamamoto, Y.; Asano, N.
Chem. Rev. 1993, 93, 2207.
(2) (a) Kobayashi, S.; Nishio, K. Tetrahedron Lett. 1993, 34,
3453. (b) Kobayashi, S.; Nishio, K. J. Org. Chem. 1994, 59,
6620. (c) Ogawa, C.; Sugiura, M.; Kobayashi, S. Chem.
Commun. 2003, 192; and references therein.
(3) (a) Kobayashi, S.; Hirabayashi, R. J. Am. Chem. Soc. 1999,
121, 6942. (b) Hirabayashi, R.; Ogawa, C.; Sugiura, M.;
Kobayashi, S. J. Am. Chem. Soc. 2001, 123, 9493.
(c) Ogawa, C.; Sugiura, M.; Kobayashi, S. J. Org. Chem.
2002, 67, 5359. (d) Kobayashi, S.; Ogawa, C.; Konishi, H.;
Sugiura, M. J. Am. Chem. Soc. 2003, 125, 6610; and
references therein.
HO
a) NHMDS (1.2 equiv)
NH2
THF, 0 °C then
HN
MeI (2 equiv), r.t. (77%)
Ph
Ph
b) PhI(OAc)2 (4 equiv)
MeOH, r.t.
syn-9 (86% syn)
syn-8 (86% syn)
then 1N HCl (40%)
HO
(4) We have successfully utilized 2-aminophenols-derived
imines for chiral zirconium-catalyzed asymmetric reactions.
For leading references, see: (a) Ishitani, H.; Ueno, M.;
Kobayashi, S. J. Am. Chem. Soc. 2000, 122, 8180.
(b) Mannich-type reaction: Kobayashi, S.; Kobayashi, J.;
Ishitani, H.; Ueno, M. Chem.–Eur. J. 2002, 8, 4185.
(c) Allylation using allyltributyltins: Gastner, T.; Ishitani,
H.; Kobayashi, S. Angew. Chem. Int. Ed. 2001, 40, 1896.
(5) General procedure for allylation: To a solution of imine 3
(0.3 mmol) and 2-methyl-2-butene (0.3 mmol) in DMF (0.3
mL) was added dropwise allylic trichlorosilane 4 or 6 (1.5
equiv) at 0 °C. After stirring vigorously for 5 h at the same
temperature, triethylamine (0.2 mL) in methanol (1.0 mL)
was added to quench the resulting viscous solution. The
mixture was diluted with diethyl ether (40 mL) and water (20
mL). The organic layer was separated, washed twice with
water (20 mL), dried over anhydrous Na2SO4, filtered, and
purified by preparative TLC (hexane/ethyl acetate, 6:1) to
give adduct 5 or 7.
NH2
Ph
a) K2CO3, MeI
HN
Ph
acetone, r.t. (81%)
b) PhI(OAc)2 (4 equiv)
MeOH, r.t.
anti-9 (>99% anti)
anti-8 (>99% anti)
then 1N HCl (55%)
Scheme 3 Deprotection of hydroxyphenyl groups.
In summary, we have demonstrated for the first time that
imines derived from aldehydes and 2-aminophenols react-
ed with allyltrichlorosilanes in the presence of a neutral
coordinate-organocatalyst to afford homoallylic amines in
high yields. It is noteworthy that the directing effect of the
hydroxyl groups proximal to the imine nitrogen has been
suggested. Moreover, crotylation using (E)- and (Z)-crot-
yltrichlorosilanes showed high stereospecificity to give
syn- and anti-adducts.
(6) Porter, J. R.; Traverse, J. F.; Hoveyda, A. H.; Snapper, M. L.
J. Am. Chem. Soc. 2001, 123, 10409.
(7) Phenyliodonium dicarboxylate-mediated intra- and
intermolecular carbon-carbon bond-forming reactions of
phenols with alkenes were reported, see: (a) Swenton, J. S.;
Carpenter, K.; Chen, Y.; Kerns, M. L.; Morrow, G. W. J.
Org. Chem. 1993, 58, 3308. (b) Quideau, S.; Pouységu, L.;
Oxoby, M.; Looney, M. A. Tetrahedron 2001, 57, 319.
(8) Products 8 were prepared from crotylation of 2-amino-p-
cresol/benzaldehyde-imine under the conditions similar to
crotylation of 3a (Scheme 1). The reactions with (E)- and
(Z)-6 at r.t. for 5 h provided syn-8 (74% yield, 86% syn) and
anti-8 (76% yield, >99% anti), respectively.
Acknowledgment
This work was partially supported by CREST and SORT, Japan
Science Technology Corporation (JST), and a Grant-in-Aid for Sci-
entific Research from Japan Society of the Promotion of Science
(JSPS). FR thanks JSPS for a postdoctoral research fellowship.
(9) Hoffmann, R. W.; Endesfelder, A. Liebigs Ann. Chem. 1987,
215.
Synlett 2003, No. 11, 1749–1751 ISSN 1234-567-89 © Thieme Stuttgart · New York