The Use of Samarium Enolates, A Novel Alternative in the Addition Reactions to Imines
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tion of 0.1 N HCl (10 mL) was then added and the aqueous
phase was extracted with diethyl ether (3ꢅ10 mL). The
combined organic layers were dried over anhydrous Na2SO4,
filtered and concentrated under vacuum. Flash column chro-
matography on silica gel (hexane/EtOAc, 3:1) provided
pure compounds 3 or 4.
In the case of compound 3e, the samarium enolate was
previously formed at ꢀ208C and the imine 1e was added
subsequently. The reaction mixture was stirred at the same
temperature for 30 min and then was left to reach room
temperature for 3 h. After the corresponding hydrolysis and
the purification the product 3e was isolated in the pure
state.
(0.4 mmol) in CH2Cl2 (10 mL) at 08C. The reaction mixture
was left to stir at room temperature for 12 h. An aqueous
solution of 1 N HCl (10 mL) was added and the aqueous
phase was extracted with CH2Cl2 (3ꢅ10 mL). The combined
organic layers were washed with 1 N HCl, dried over anhy-
drous Na2SO4, filtered and concentrated under vacuum.
Flash column chromatography on silica gel (hexane/EtOAc,
3:1) provided pure compound 10 with the same spectroscop-
ic data to those shown by the same product prepared by
Reetz, see ref.[20]
Acknowledgements
Synthesis of 5 from 4b
We acknowledge Ministerio de Ciencia
e Innovaciꢀn
To a stirred solution of 4b (0.4 mmol) in THF (2 mL), n-
BuLi (1 mmol) was added at ꢀ788C. After stirring at the
same temperature for 1 h, the reaction mixture was
quenched with an aqueous solution of 0.1 N HCl (10 mL)
and the aqueous phase was extracted with diethyl ether (3ꢅ
10 mL). The combined organic layers were dried over anhy-
drous Na2SO4, filtered and concentrated under vacuum.
Flash column chromatography on silica gel (hexane/EtOAc,
3:1) provided pure compound 5.
(CTQ2007-61132) and Principado de Asturias (FICYT IB08-
08) for financial support. J.M.C. thanks his wife Carmen
Fernꢁndez-Flꢀrez for her time. H.R.S. and C.S. thank
MICINN for a Ramꢀn y Cajal Contract (Fondo Social Eu-
ropeo) and for a predoctoral fellowship, respectively. Our
thanks to Dr Euan C. Goddard (CRL, University of Oxford)
for his revision of the English. We thank Prof. Reetz for his
personal communication concerning the spectroscopic data
of compound 10.
Synthesis of 6 from 4b
References
Deprotection of compound 4b was carried by using the con-
ditions described in ref.[11]
[1] 3-Amino acids can be transformed into other com-
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General Procedure for the Synthesis of Compounds 8
a-Amino imines 7 were synthesized following the method
reported in ref.[17]
To a stirred solution of Sm(0) (3 equiv., 1.2 mmol), previ-
ously activated by heating, and THF (2 mL), the imine 7
(0.4 mmol), ester (0.4 mmol) and THF (10 mL) were added
at room temperature. Then, CH2I2 (3 equiv., 1.2 mmol) was
added and the reaction mixture was stirred at the room tem-
perature for 6 h. The excess SmI2 was removing by bubbling
an stream of air through the solution and further treatment
with an aqueous solution of 0.1 N HCl (10 mL). The aque-
ous phase was extracted with diethyl ether (3ꢅ10 mL). The
combined organic layers were dried over anhydrous Na2SO4,
filtered and concentrated under vacuum. Flash column chro-
matography on silica gel (hexane/EtOAc, 2:1) provided
pure compound 8.
[2] a) C. N. C. Drey, in: Chemistry and Biochemistry of the
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New York, 1985, Chapter 3; b) O. W. Griffith, Annu.
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Mannich-Bases: Chemistry and Uses, CRC, Boca
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[4] For reviews on b-peptides, see: a) S. H. Gellman, Acc.
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General Procedure for the Synthesis of Compound 9
To a stirred solution of crude material 8 in CH2Cl2, was bub-
bled a stream of HCl (gas) for 15 min. The aqueous phase
was extracted with CH2Cl2 and the organic layer was
washed with NaHCO3 and dried over Na2SO4. After remov-
ing the solvents, a crude mixture was obtained and purified
by flash chromatography on silica gel (hexane/EtOAc, 1:1)
to yield 9 as a pure compound.
General Procedure for the Synthesis of Compound 10
Triethylamine (1,1 equiv., 0.44 mmol) and tosyl chloride
(1.1 equiv., 0.44 mmol) were added to a stirred solution of 9
Adv. Synth. Catal. 2009, 351, 1238 – 1242
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