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Functionalization at Proanomeric Centres by Photobromination A Novel Access to Oxo- and Acyloxyimino-glycosyl Bromides.

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151 M. Tanaka, K. Kitaoka, H. Okawa, S. Kida, Bull. SOC.Chim. Jpn. 49
(1976) 2469.
161 The theoretical magnetic susceptibility was derived from the spin Hamil.Sc, ZJ'~,(.%)lwhere the symtonian [ W=@c.Sc. +gc,&JfM-J&,
bols have their usual meaning. The last term accounts for the intermolecular interaction.
-
Functionalization at Proanomeric Centres
by Photobromination: A Novel Access to
0 x 0 - and Acyloxyimino-glycosyl Bromides* *
By Frieder W. Lichtenthaler* and Pan Jarglis
Dedicated to Professor Hermann Schildknecht on the
occasion of his 60th birthday
The range of reactions undergone by sugars at the
anomeric centre form the backbone of carbohydrate chemistryf2I.In contrast, reactions of monosaccharides at their
proanomeric centres, i.e. those which become anomeric by
introduction of a functional group at C-4 in furanoid or at
C-5 in pyranoid systems, are rare; they usually involve elaboration of a double bond in the proanomeric position and
subsequent addition reactionsf3] or free-radical brominationL4I which, however, mostly give low to moderate
yields.
By placing an electron acceptor group, i.e. 0x0- or acyloxyimino functionalities next to the proanomeric centre,
its C-H bond becomes push-pull-or capt~-dativeIy~'~substituted, and, hence, highly radicophilic. Thus, radical
reactions proceed with considerably greater ease with
higher regio- and stereoselectivity, as is amply demonstrated by the smooth, high yield photobrominations of
1-6 (cf. Scheme 1).
With 1 and 2, photobromination is essentially stereospecific, and no products other than a-glycosyl bromides 7
and 8 are obtained which have high potential for the preparation of a- and p-linked glycosyl glycosides. Enolones
are also readily accessible, since alcoholysis under slightly
basic conditions is accompanied by p-elimination. Accordingly, upon in situ anomerization with tetraethylammonium bromide followed by methanolysis 7 preferentially
affords (isolated yield: 66%) the a-D-enolone (3, OMe instead of a-OBz), whereas exposure to methanol in the
presence of NaHCO, yields the respective 8-D-anomer
(80%).
In the tribenzoyl enolone 3 the proanomeric centre is vinylogously push-pull activated, yet due to the presence of
only one conformationally determining substituent in the
radical intermediate, a 3 :1 mixture of anomers result, of
which the major, a,a-isomer 9, is isolable in 51% yield.
Utilization of hydroxyimino functions as the captive
("pull") element of a capto-dative system also requires
protection of this OH group, which is most suitably effected by benzoylation. Thus, the peracylated 1$anhydroD-fructose derivatives 4 and 5 readily give the oximinoglycosy1 a-bromides 10 and 11 in high yield. The availability
of such a-bromides in stable, storable form is capable of
providing an efficient access to amino sugar-containing oligosaccharides by simple displacement of the bromine via
a Konigs-Knorr glycosylation reaction, reduction, and deblocking. This approach has close analogies to Lemieux's
nitroso-halogenide procedurer2'], yet holds the additional
advantage that disaccharide-derived analogs of 10 and 11,
which constitute versatile building blocks for the construction of lactosamine-, maltosamine-, and cellobiosaminecontaining oligosaccharides, may easily be prepared. The
OB z
RO
I
2
v
NBSlhv
82%
VYL.
7
4 , R = R' = Bz
5 , R = Ac; R' = pNBz
3
NBSlhu
\
NBSlhv
87191%
,
OB z
BzO
8
KVlU
0
9
6
1
'
Br
Br
10, R = R' = Bz
11, R = Ac; R' = pNBz
NBSIhv
83%
12
Scheme 1. Photobrominations in refluxing CCL by irradiation with a 250W tungsten lamp or a 450W IR heat lamp, 15-60 mh-Abbreviations: Ac=acetyl;
Bz= benzoyl; pNBz-p-nitrobenzoyl; NBS = N-bromosuccinimide.-New educts: 2 (m.p. = 190-192 "C, [a]: - 10" in CHCI,, 94%) by pyridinium chlorochro4 (m.p.= 138--139"C, [a]: -37" in CHCII, 91%) and 5 (89-9OoC, -70", 85%) by acylation of the free
mate oxidation of 1,2,3-tri-O-benzoyl-a-L-rhamnose;
oximes I201 with benzoyl chloride and p-nitrobenzoyl chloride/pyndine, resp.-Products: 7 (m.p.= 174% [a]: 185" in CHCI,), 8 (118-119"C, + 109"), 9
(181-183 "C, -21 "C), 10 (138-139 "C, -37 "C), 11 (amorph., 156 "C), 12 (92 "C, + 137"C).-For 'H-NMR data and experimental procedures for 7 , 10, and
12 see Supplement.
+
+
[*] Prof. Dr. F. W. Lichtenthaler, Dr. P. Jarglis
Institut fur Organische Chemie
der Technischen Hochschule Darmstadt
Petersenstrasse 22, D-6100 Dannstadt (Germany)
[**I Sugar Enolones, Part 16. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industfie.-Part
15: P. Jarglis, F. W. Lichtenthaler, Angew. Chem. 94 (1982) 140; Angew.
Chem. In;. Ed. Engl. 21 (1982) 141; Angew. Chem. Suppl. 1982, 175.
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 8
nitrile 6 can also be readily photobrominated at the pushpull substituted proanomeric centre.
Attempts to prepare the chloride analog of 7 by photobromination of 1 with N-chlorosuccinimide under a variety of conditions failed. However, refluxing 1 and 4 in
cc14with sulfonyl chloride/azobisisobutyronitrile
(3-4
h, 76 "C) leads cleanly to the respective, highly stable a-
0 Verlag Chemie GmbH, 6940 Weinheim. 1982
0570-0833/82/0808-0625 $02.50/0
625
glycosyl chlorides 7 (C1 instead of Br, m. p. = 153- 154 "C,
[a]g 155" in CHC13, 87%) and 10 (C1 instead of Br, sy198" in CHC13, 90%).
rup, [a]?
+
Table 1. "C-NMR data (6 values) of 1 and 2; solvent: C6Db;temperature:
30 " C ; concentration f a . 15%.
+
Received: April 15, 1982 [Z 12 IE]
German version: Angew. Chem. 94 (1982)643
The complete manuscript of this communication appears in:
Angew. Chem. Suppl. 1982, 1449-1459
2
1
C-atom
I
2
3
11
121 Review: F. Bochkov, G. E. Zaikov: Chemistry of the 0-Glycosidic Bond,
Pergamon, Oxford 1979.
I31 B. Helferich, N. M. Bigelow, 2.Physiol. Chem. 200 (1931) 263; L. Zervas, 1. Papadimitrou, Ber. Dtsch. Chem. Ges. 73 (1940)174;J. Lehmann,
E. Pfeiffer, H. Reinshagen, Chem. Ber. 102 (1969)2745; 1. D. Jenkins, J.
P. H. Verheyden, J. G. Moffat, J. Am. Chem. SOC.98 (1976)3346.
[4] R. J. Ferrier, R. H . Furneaux, J. Chem. SOC.Perkin Trans. I 1977, 1996;
R. J. Ferrier, P. C. Tyler, ibid. 1980, 1528,2767; R. Blattner, R. J. Ferrier,
ibid. 1980, 1523.
[7] H.G. Viehe, R. Merenyi, L. Stella, Z. Janousek, Angew. Chem. 91 (1979)
982;Angew. Chem. Int. Ed. Engl. 18 (1979)917.
[20] F. W. Lichtenthaler, P. Jarglis, Tetrahedron L e f f .21 (1980) 1425.
[2l] R. U. Lemieux, Y. Ito, K. James, T. L. Nagabhushan, Can. J. Chem. 51
(1973)7; R. U. Lemieux, K. James, T. L. Nagabhushan, ibid. 51 (1973)
42, 48.
12
21
22
I
I
F value
C-atom
6 value
130.20
70.99
76.58
102.20
58.91
106.90
56.39
31
32
33
41
42
43
51
52
53
61
62
63
130.58
72.79
75.80
135.24
69.68
76.23
102.88
57.94
54.64
104.96
55.27
54.01
1
I
1
1
1
1-
Two-Dimensional Dynamic I3C-NMR SpectroscopyAn Investigation of ( I ~ ' - C ~ H ~ ) ~ C ~ ~
4-4
2
By Reinhard Benn*
Chemical exchange processes were hitherto investigated
NMR spectroscopically almost solely by line-shape analysisL'land magnetization-transfer methods''l. It has already
been shown[31that exchange networks can be obtained directly with the aid of two-dimensional NMR spectroscopy
(2D-NMR). In the following it is demonstrated with tetraallyldichromium (q3-C3H5)4Cr2as example, that two-dimensional '3C-'3C-shift correlation diagrams are especially suitable for the qualitative investigation of exchange
processes.
''j
110
I
1'
1
In [D,]benzene at 30°C (q3-C3H5)4Crzis present as a
60:40 mixture of the isomers 1 and 2. Each isomer has
two trans q3-allyl groups bridging the metal atoms. The
other two q3-allyl ligands are cis-oriented in 1 and transoriented in 2I4I. Accordingly, the noise-decoupled I3CNMR spectrum of 1 shows seven signals, that of 2 twelve
signals (Table 1); these were assigned on the basis of a
two-dimensional I3C-'H-shift correlation diagram"] using
the 'H chemical shiftsc4'.
The structural dynamic behavior of 1 and 2 can be deduced from the two-dimensional '3C-'3C-~hiftcorrelation
Max-Planck-lnstitut fur Kohlenforschung
Kaiser-Wilhelm-Platz 1, D-4330 Mulheim a. d. Ruhr (Germany)
626
0 Verlag Chemie GmbH. 6940 Weinheim, 1982
-2
-
100
6"")
Fig. 1. Top: Conventional one-dimensional "C-NMR spectrum (100.61
MHz).-Bottom: Section from the two-dimensional '3C-"C shift correlation
diagram of (q3-C3Hs)&r2 in [D,]benzene (S= 128.5); recorded with a 90"(~I/~)-~O~-A-~OO-(~~/~)-FID(~~)
pulse sequence 131. tI was varied from 0 to
0.0256 s over 256 points, the mixing time A was 2 s. The "C-NMR signals are
represented on the horizontal axis, and shift differences on the vertical axis.
Exchanging "C-atoms appear as cross peaks and are connected together.
2
[*I Dr. R. Benn
t
1
diagram without a detailed knowledge of the assignment.
A section from the contour plot of the 13C-13C-shiftcorrelation diagram is shown in Figure 1. The positions of the
l3C-NMR signals are given as contour lines on the middle
line; for clarification the conventional one-dimensional
I3C-NMR spectrum is reproduced at the top of Figure 1.
In the two-dimensional spectrum further contour lines, socalled cross peaks, appear above and below the middle
line. Differences in the I3C chemical shifts are indicated on
the vertical axis ; related cross peaks have the coordinates
[6, ; (6, - 6,)l and [6, ; 4 (6,e. g. the cross
peaks of C21 and C11 connected by an extrapolated line
have the coordinates (106.90; 2.35) and (102.20; -2.35).
These cross peaks provide direct evidence of an exchange
of C21 with (211, which is caused by a 180" rotation of the5
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0570-0833/82/0808-0626 $02.50/0
Angew. Chem. Int. Ed. Engl. 21 (1982) No. 8
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centred, functionalization, acyloxyimino, glycosyl, novem, oxo, access, bromide, proanomeric, photobromination
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