10.1002/adsc.201901298
Advanced Synthesis & Catalysis
Acknowledgements
To complete the synthetic route to chiral N-
unprotected-2-aminoalkan-1-ols from hydrogenation
products, we examined the deprotection of the pyrrolyl
amine group in 2a (Scheme 1). The use of NH2OH in
refluxing EtOH/H2O (3/1, v/v)[22] and the ozonolysis
in MeOH at –78 °C[23] were both effective, affording
2-amino-3-phenylpropan-1-ol (4a) in isolated yields
of 53% and 60%, respectively. Racemization was not
observed in the 4a produced by either of the two
different deprotection methods.
This work was supported by the Nagase Science and Technology
Foundation as well as partially by a Grant-in-aid for Scientific
Research on Innovative Areas (18H04247) and for Scientific
Research (B) (19H02713) from MEXT and JSPS, respectively. SY
gratefully acknowledges an IGER fellowship (NU).
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Scheme 1. Deprotection of the pyrrolyl group of 2a.
In conclusion, we have demonstrated that the
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For further information of experimental procedures and data,
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Representative procedure for the hydrogenation of 1a
with Ru-1: N-protected (S)-phenylalanine (1a, 107.6 mg,
0.5 mmol), Ru-1 (12.8 mg, 0.015 mmol), and a magnetic
stirring bar were placed in a glass tube (21 mL), which was
inserted into an autoclave that was closed tightly and refilled
with Ar. Under a continuous flow of Ar, anhydrous toluene
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10 times with H2 (ca. 1 MPa) and then pressurized at 25 °C
with H2 (4 MPa) and subsequently heated to 110 °C for 24
h under stirring (500 rpm). Thereafter, the autoclave was
cooled to ca. 25 °C in an ice–water bath (0 °C). The reaction
mixture was transferred into a round-bottom flask (100 mL)
with CHCl3 and concentrated under a reduced pressure (ca.
30 mmHg, 40 °C). The thus obtained residue was dissolved
in CDCl3 and analyzed by 1H NMR. The yields of 2a (80%)
and 3a (2%) were calculated based on the integral ratio
between the signals of these compounds with respect to an
internal standard (mesitylene). The crude mixture was
purified by column chromatography on silica gel (eluent:
hexane/ethyl acetate = 4/1), giving 2a (75 mg, 0.37 mmol,
74% yield) as a brown oil.
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5
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