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Cyclorearrangement of 3 4 5-Tri-O-acetyl- (1 2 43 5)-cyclopentanepentol-1 2-O-acetoxonium Tetrafluoroborate.

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pivalate, on the other hand, affords (8b) (43%) and (9b)
(57 "/,). The ion (86) exhibits a rapid rearrangement (8b) .+
(lob) (see Table 1) whereas the ion (9b) does not. The salt
(Pb), from which (1,2,3/0)-cyclopentanetriol is easily accessible, can be obtained by crystallization from a mixture of the
hexachloroantinionates of ( 8 b ) and ( 9 b ) . Thecation (11) also
exhibits a rapid valence isomerization (11) +(12) (see
Table 1). ( I l l is best prepared as the tetrafluorobordte by
removal of hydride from 3-O-acetyl-1,2-O-ethylidene(1,2/3)-cyclohexanetriolwith (C6Hs)3C@BFd0.
4-Aceioxymethyl-2-mefhyI-I,3-dioxolnn-2-ylium
hexachloroantimonate (Sa)
SbC15 (4.5 ml) is dissolved in CHzCl2 ( 5 ml) and then added
dropwise with stirring at -10 "C to a solution of glycerol triacetate (7.7 g) in anhydrous CHzCl2 (7 ml). After 24 h a t
room temperature the acetoxonium salt (5a) crystallizes
(yield SO%, m.p. 145-148 "C).
Received: August 29, 1969
[Z 98a IE]
German version: Angew. Chem. 81, 905 (1969)
[*I Prof. Dr. H. Paulsen and Dip].-Chem. H. Behre
Institut fur Organische Chemie der Universitat
2 Hamburg 13, Papendamm 6 (Germany)
[l] Part 7 of Carboxoniurn Compounds in Carbohydrate Chemistry. Part 6: F. Garrido Espinosa, W. P. Trautwein, and H . Paulsen, Chem. Ber. 101, 191 (1968).
[2] H . Meerwein, V . Hederich, and K. Wunderlich, Arch. Pharmaz. 291, 541 (1958); H. Meerwein, K . Bodenbenner, P. Borner,
F. Kunerf, and K . Wunderlich,Liebigs Ann. Chem. 632,38 (1960);
H . Meerwein, V . Hederich, H . Morschel, and K . Wunderlich, ibid.
635, 1 (1960).
[ 3 ] C. B. Anderson, E. C . Friedrich, and S . Winstein, Tetrahedron
Letters 1963, 49.
Cyclorearrangement of 3,4,5-Tri-O-acetyl(1,2,4/3,5)-cyclopentanepentol-l,2-O-acetoxonium
Tetrafluoroborate
By H . Paulsen and H . Behre[*]
In acyloxonium salts of 1,2,3-triols a rapid valence isomerism
takes place between the two possible dioxolanylium cations [I]. The AG* value of this rearrangement is lower in the
case of (1,2/3)-cyclopentanetriolderivatives than it is in the
case of glycerol or (1,2/3)-cyclohexanetriolcompounds, since
the neighboring group reaction 121 in the cyclopentane ring is
apparently sterically favored. As was to be expected, we have
found that a total valence isomerization takes place in the
cyclopentanepentol system.
Penta-O-acetyl-(l,2,4,'3,5)-cyclopentanepentol reacts heterogeneously with SbCIS. We therefore prepared 3,4,5-tri-Oacetyl-l,2-O-et hylidene-(l,2,4/3,5)-cyclopentanepentol ( I ) by
reaction of the free pentolE31 with acetaldehyde diethylacetal
and subsequent acetylation. [ ( l )consists of 65% of the ex0
form (m.p. 120 "C) and 35 % of the endo form (m.p. 110 "C)].
The acetal ( I ) reacts with (C6H5)3CBBFqQ in CH3CN with
loss of hydrideE41 to give the BF40 salt of (2). By successive
neighboring group reactions the cation (2) can be converted
into a second cation that is structurally identical with (2).
The prerequisites for a neighboring group reaction are fulfilled at each stage of the conversion. After ten conversion
steps the starting material is re-formed.
The N M R spectrum of the acetoxonium salt (2) in CD3CN
at room temperature contains a n acetoxonium methyl signal
a t low field strength with T = 7.13 (3H) and two signals due
to normal methyl groups at 7 = 7.90 (6 H) and T = 7.95 (3 H).
At 80 OC all signals are considerably broadened, thus indicating that at this temperature the rearrangement is rapid
according to the N M R time scale. Careful integration of the
changed methyl signals shows that all the acetyl methyl
groups participate in the process; this can be considered as
proof that the substance undergoes rearrangement in the
manner mentioned. The exact coalescence temperature cannot be determined since (2) rapidly decomposes at temperatures above 8OoC. The value of AG+ can be estimated as
being approximately 18 kcal/mole by extrapolation and comparison with the heating curves of the acetoxonium salts of
1,2,3-triols.
We have also examined whether "jumping" takes place
during the cyclic rearrangement, i.e. whether a C-atom can
be "jumped over" via 1,3-neighboring group reaction. If this
were the case then other isomers of cyclopentanepentol
would have to be formed. G L C analysis of the hydrolyzed
reaction mixture showed that other isomeric cyclopentanepentols 151 are formed in amounts of 3 %.
Received: August 29, 1969
[Z 98b IEI
German version: Angew. Chern. 81, 906 (1969)
[*] Prof. Dr. H. Paulsen and DipL-Chem. H. Behre
Institut fur Organische Chemie der Universitat
2 Hamburg 13, Papendamm 6 (Germany)
[l] H . Paulsen and H. Behre, Angew. Chem. 81, 905 (1969);
Angew. Chem. internat. Edit. 8, 886 (1969).
[2] S . Winstein and R . E . Buckles, J. Amer. chem. Soc. 64, 2780,
2787 (1942).
[ 3 ] H . Z . Sable, Th. Anderson, B. Tolbert, and Th. Posternak,
Helv. chim. Acta 46, 1157 (1963).
[4] H . Meerwein, V. Hederich, H . Morschel, and K . Wunderlich,
Liebigs Ann. Chem. 635, 1 (1960).
151 Th. Posternak and G. Wolczunowicz, Naturwissenschaften
55, 82 (1968).
II,C
OAc
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cyclorearrangement, cyclopentanepentol, acetoxonium, tri, tetrafluoroborate, acetyl
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