10.1002/anie.201800057
Angewandte Chemie International Edition
COMMUNICATION
ring-opening with methanol under mildly acidic conditions, reduction of
the N-acyl pyrazole group with NaBH4, and subsequent saponification
of the methyl ester. By taking advantage of the remaining diene moiety
in 8, δ-valerolactone 9[15] was produced by a diastereoselective
selenolactonization followed by the removal of the vicinal hydroxyl and
selenenyl groups.[22] Then, selective ozonolysis of the pendant vinyl
group was reductively quenched with NaBH4 and, after reduction of the
lactone carbonyl, diastereoselective syn-dihydroxylation of the
endocyclic olefin by the modified Baran’s procedure yielded aza-sugar
derivative 10.[23] Finally, acetylation of free hydroxyl groups of 10 with
concurrent isomerization of the pyranose core to the furanose form gave
Keywords: amino acid • Michael addition • iminophosphorane •
hexosamine • organocatalysis
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HO
O
O
a~c
d,e
f~h
HO2C
Me
Me
1,6--Z,E-5a
Ar1OCN
Ar1OCN
H
H
8
9
OAc
HO
Me
O
O
i
AcO
Ar1OCN
[8]
[9]
OAc
OH
Ar1OCN
H
H
HO
OAc
Me
11
OH
10
11
ORTEP of rac-
Scheme 3. Derivatization to 2-Amino-2-deoxy-2-Me-D
-altrofuranose (Ar1 = 2,6-
(MeO)2C6H3). Conditions: a) PPTS, MeOH, 0 °C; b) NaBH4, MeOH, –20 °C; c)
KOH, MeOH, 70 °C (>99% in three steps); d) (PhSe)2, (PhSO2)2NF, CH2Cl2, MS
4Å, –20 °C (60%); e) PBr3, CH2Cl2, 0 °C (70%); f) O3, MeOH/CH2Cl2, –78 °C,
then NaBH4, –78 °C (87%); g) DIBAH, CH2Cl2, –78 °C (>99%, dr = 2.5:1); h)
OsO4, NMO, citric acid, tBuOH/acetone/H2O, 50 °C; i) AcCl, Et3N, DMAP,
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In conclusion, we established two distinct catalytic systems for
achieving a site-divergent, highly diastereo- and enantioselective
Michael addition of α-amino acid-derived, prochiral azlactone enolates
to enynyl N-acyl pyrazoles under mild conditions. The key is the ability
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substrates with precise control of multiple selectivity factors. The
synthetic value of the structurally and configurationally homogeneous
conjugated dienes was highlighted by the concise assembly of a 2-
amino-2-deoxy sugar, which substantiates the potential impact of the
stereoselective 1,6-addition protocol on the synthesis of complex targets.
We believe that the catalyst-directed site-divergent strategy significantly
expands the synthetic potential of the Michael reactions with extended
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Acknowledgements
Financial support was provided by CREST-JST (JPMJCR13L2:
13418441), Program for Leading Graduate Schools "Integrative
Graduate Education and Research Program in Green Natural Sciences"
in Nagoya University, and Grants of JSPS for Scientific Research. N.
Tanaka, K. Yamada, and K. Yoshioka acknowledge JSPS for financial
support.
[15] Crystallographic data (excluding structure factors) for 1,4-5a, 1,6-γ-Z,E-
5g, 9, and rac-11 have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-
1813740, CCDC-1813741, CCDC-1813742, and CCDC-1813882,
respectively. Copies of the data can be obtained free of charge on
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