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Multiple 1 2-O O-Shift of tert-Butyldiphenylsilyl Groups in Polyols.

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[7] M. Bianchi, U. Matteoli. P. Fredrani, F. Piacenti, U. Nardelli, G. Pelizzi.
('/inti Ind. iMilun) 63 (1981) 475.
[ X I Crystal structure data: The structure was determined with a Stoe-Siemens
AED2 four-circle diffractometer (Mo,,, graphite monochromator,
i = 0.71073 A) using SHELXS-86 [9] and refined with SHELX-76 [lo]. 5 :
space group R3. three independent molecules A, B and C per asymmetric
unit. thc crystal contains randomly distributed uncoordinated MeCN
z = /3 = 90'.
molecules u = 17.544(1), h = 17.544(1). c = 62.005(5)
;.=120.
V=16528.1A3, 2 = 9 , ~,,,,,,=1.500gcm3. p = 1 1 . 5 c m - ' ,
O,,,, = 25 ; 6016 independent reflections, only Lp correction; index limits
ii
18!18. k : =0/20. I : 0/73;4833 reflections with Fo > 5 G ( F , , ) ;hydrogen
atoms of the OH groups could not be located; refinement with weighted
anisotropic temperature factors by the least squares method gave
R = 0.051. R , = 0.050 with I(.-' = ~'(f;,)+ 0.0094 (Fg). Residual density
in the last difference map 1.12(max) in the neighborhood of the CH,
carbon atoms of an uncoordinated MeCN molecule. -0.62 (min) k 3 .
Further details of the crystal structure investigation are available on request from the Director of the Cambridge Crystallographic Data Centre.
University Chemical Laboratory. Lensfield Road. Camhridge CB2 1EW
( U K ) . o n quoting the complete literature citation.
[9] G M Sheldrick, "SHELXS-86". Program for Crystal Structure Determination. Universitit Cottingen 1986.
[lo] ti M Sheldrick, "SHELX-76". Program for Crystal Structure Determination. University of Cambridge (UK) 1976.
[ l l ] W. D. S. Motherwell. W Clegg, "Pluto". Program for Plotting Molecular
and Crystal Structures, University of Cambridge (UK) 1978.
and 4 a in 20 min, from which 4 b can be separated and used
again. After 15 min, the same product ratio as from 4a is
obtained, thus proving that the silyf migration proceeds reversibly in both directions. Responsible for the equilibrium
A,
OR^
4
w
I
R1
R2
R3
H
tBuPh,Si
H
~
Multiple 1,2-O,O-Shift of tevt-Butyldiphenylsilyl
Groups in Polyols
By Johunn Mulzer * and Bernd Schijllhorn
tert-Butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) groups are standard protecting groups for
OH functions.['] The 0 , O silyl migration to be expected in
polyols was hitherto chiefly observed in the case of the less
stable TBDMS unit."' In the case of the TBDPS group two
examples have been described in the literature, namely a
1 , 3 - ~ h i f t ' ~and
] 1,2-~hift.[~]
We now report a multiple 1,20 , O migration of TBDPS groups in the polyol derivatives 1,
2, 4-6, 8, 9 and 13.151
OR'
Me
Me
-
&OR2
1
1
H
Me
OR2
V+o
OR'
OSiPh,tBu
2
3
OR2
H
4
position is the preference of the bulky TBDPS group for the
primary position, which is favored by ca. 8-9 kJ mol- compared to the secondary positions, but, because of the reversibility of the migration step, is only reached by trial and
error. The establishment of equilibrium therefore takes
longer the larger the number of the participating OH functions.
The pentol 5a derived from D-mannitol isomerizes to 5b,
which, because of the C , symmetry of the unprotected mol-
'
OH
OH
5
-
O
2R
*H
o
-
OH
OR'
R1
a
tBuFk3i
b
H
2
H
tB&I@
ecule, can be formed by two- or threefold 0 , O migration.
Both routes are possible, as demonstrated by the uniform
formation of 7 from 6a and 6b. The syn- or anti-position of
the OH functions to be traversed, and thus the conformational strain in the postulated intermediate Z,['"I apparently
have no influence on the product pattern. This experiment
also proves that the silyl migration--consistent with Z-proceeds with retention at the carbinol centers, since 7 would
otherwise be epimerized differently compared to the precursors 6a/b.
2
a, R = tBuFh2Si, R = H
1
2
b, R = H , R = tBuPh2S
The silyl migration requires base catalysis (standard conditions: potassium carbonate in methanol, 22 "C). 1 a and 2 a
then isomerize completely to 1b and 2 b, respectively. Under
neutral or acid conditions the TBDPS group is stable towards migration. Reduction of the aldehyde 3 with lithium
aluminum hydride in diethyl ether therefore leads uniformly
to 2a, whereas that with sodium tetrahydroborate in methanol yields 2 b quantitatively. During the reaction 2a is detectable as intermediate.
Under standard conditions, the trio1 derivative 4a forms
an 87:7:6 equilibrium mixture (HPLC analysis) of 4c, 4b
[*I
a
H
bI
-CM%-
H
-CM%H
H
Prof. Dr. J. Mulzer, DipLChem. B. Schollhorn
Institut fur Organkche Chemie der Freien Universitit
TdkuStraSSe 3. D-1000 Berlin 33.
A n m c . Chhrm. Inr. Ed. EngI. 29 11990) No. 4
8;'
V C H Verlu~.~~esell.~~hafi
mhH, 0.6940 Weinbrim.1990
I
7
0570-0~33/~0/0404-0431
$02.50/0
43 1
By incorporation of a methyl branch, the migration in the
direction of this branching is prevented: under standard conditions derivative 8 a affords only 8b; of the two monoacetals 9, 9 a remains unchanged, whereas 9 b quantitatively
forms 10, which furnishes 8 b again upon cleavage of the
acetal. A 1,3 shift"] apparently does not take place. To fur-
Me
R
o2-4H
-o
OH
OH
R1
a
tBuF%$i
H
b
Rlo&oR4
OR'
8
OH functions are recognized by the OH multiplet, secondary
OH functions by the OH doublet.r5]
Also cyclic I,2-diols display the phenomenon of TBDPS
migration. Thus, the glucose derivative 13 a is silylated with
TBDPS chloride under kinetic conditions to give a 94:6 mixture of the monosilyl ethers 13b and I3c. Under our standard conditions, however, a 2: 1 mixture of 13e and 13 b is
formed within a few minutes. Thus, kinetic and thermodynamic control afford extremely different results.
OR2
F?
H
tBuPh$i
9
a
b
R1
OSiPh2tBu
R2
R3
R4
phT+-+
R' 0
H
H
-CM%-
-%- H
13
R1
2
ab
OMe
c
tBuP&Si
H
HH
H
tBd?&Sa
13
H
8b
t
10
ther check this finding the 1,3-diol 11 a was investigated.
Under standard conditions it does not isomerize to 11 b; only
concentrated methanolate enforces this reaction, albeit with
a small conversion over several days.
OR'
11
m
A
OR2
0
\
-
-0
I
a
bl
R1
€?
tBuE'h$i
H
H
tBuFh$i
These findings can be exploited preparatively, on the one
hand to obtain terminally monosilylated polyols such as 5 b
or 8 b without having to deal with the relatively strongly
hydrophilic and thus difficultly handleable free polyols;
small amounts of secondary silyl ethers can be readily separated by column chromatography. On the other hand, two
primary terminal groups can be easily differentiated via this
migration. Thus, 7 is readily accessible from 6, and its free
secondary OH functions can then be benzylated together.
Finally, the terminal protecting groups can be removed, separately. The same is also accomplished with the methyl
derivatives 8 and 9, so that such large monosaccharides
blocks can be used in "ex-chiral pool syntheses".
General Procedure
A mixture of TBDPS-protected polyol (1 .O g in 10 mL of methanol) and saturated methanolic potassium carbonate solution was stirred at 22 "C for 10 min
to 12 h (TLC control). The mixture was then neutralized with saturated ammonium chloride solution, evaporated down (rotary evaporator), taken up in
dichloromethane, washed with water, dried over magnesium sulfate, and chromatographed on silica gel with hexane/ethyl acetate or ethyl acetate/methanol
(5b/8b). By using a few drops of methanolic sodium methanolate solution
instead of potassium carbonate the rate of migration of the silyl group could be
increased considerably
11
Received: December4, 1989 [Z 3671 IE]
German version. Angew. Chem. 102 (1990) 433
The silyl group migrates intramolecularly. This follows
from the fact that di- or desilylation have never been observed under standard conditions. Also diol 12 added to 4a
is recovered unsilylated after establishment of the equilibrium of 4, despite the two primary OH functions.
Of the products mentioned so far are unThe
equivocally confirmed via the H-NMR spectrum; primary
432
0 VCH
Verlagsgeselischaft mhH, D-6940 Weinheim, 1990
CAS Registry numbers:
la, 125803-66-9; lb, 125803-68-1;Za, 125803-67-0; Zb, 125803-69-2; 3, 12580370-5; 4a, 125803-71-6; 4b, 125803-72-7; 4c, 125803-73-8; 5a, 125803-74-9; 5b,
125803-75-0; 6a, 125803-76-1; 6b, 125803-77-2; 7, 125803-78-3; 8a, 125803.794; 8b, 125803-80-7, 9a, 125827-91-0; 9b, 125803-81-8; 10, 125803-82-9; l l a ,
125827-92-1; 12,86992-57-6; 13a. 57701-27-6; 13b, 112669-90-6,13c, 125803-0.
[ I ] E. J. Corey, A. Venkateswarlu, J Am. Chem. Soc. 94 (1972) 6190, T. Greene:
Protecrive Groups in Organic Synthesis, Wiley, New York 1981. p. 47.
[2] a) G. H Dodd, B T. Golding, P. V. Iounnou, J Chem. SOC.Perkin Trans.
f1976.2273; S S. Jones, C. B. Reese, ibid. 1979,2762; K. K. Ogilvie, S. L.
Beaucage, A. L. Schifman, N. Y. Theriault, K. L. Sadana, Can. J. Chem. 89
(1981) 203; b) W. Kohler, W. Pfleiderer, Liebigs Ann. Chem. 1979. 1855.
[3] U. Peters, W. Bankova, P. Welzel, Tetrahedron 43 (1987) 3803.
[4] J. Jurczak, S. Pikul. K. Ankner. Pol. J. Chem. 61 (1987) 767.
[ 5 ] We shall report on the synthesis, properties, and preparative use of the
compounds 2,4-9 and 10 in a separate communication.
VS70-0833/90!04(~4-0432 5 02.50/~1
Angem. Chem. Int. Ed. Engl. 29 (1990) No. 4
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