Epoxide migration and pseudo-epoxide migration of 1,6:2,3- and 1,6:3,4-dianhydro-β-D-hexopyranoses. Synthesis of some deoxy halo derivatives of 1,6-anhydro-β-D-hexopyranoses

Article abstract of DOI:10.1135/cccc20061497

Epoxide or pseudo-epoxide migration of 1,6:2,3-dianhydro- and 1,6:3,4-dianhydro-β-D-hexopyranoses was effected by treatment with aqueous sodium hydroxide or sodium iodide in acetone to give equilibrium mixtures. Various iodo derivatives of 1,6-anhydro-β-D-hexopyranoses were prepared as potential intermediates for pseudo-epoxide migration. NMR was used for following the reaction mechanism of epoxide and pseudo-epoxide migrations and analysis of reaction mixtures. Experimental data were compared with DFT calculations. Chair-boat equilibration of 1,6-anhydro-3-deoxy-3-halo-β-D-glucopyranoses was discussed.

Full text of DOI:10.1135/cccc20061497

Epoxide and Pseudo-Epoxide Migration
1497
EPOXIDE MIGRATION AND PSEUDO-EPOXIDE MIGRATION OF
1,6:2,3- AND 1,6:3,4-DIANHYDRO-β-D-HEXOPYRANOSES.
SYNTHESIS OF SOME DEOXY HALO DERIVATIVES OF
1,6-ANHYDRO-β-D-HEXOPYRANOSES
Martina DŽOGANOVÁa1,b, Miloslav ČERNÝa2, Miloš BUDĚŠÍNSKÝb1,*,
b2
a3
Martin DRAČÍNSKÝ and Tomáš TRNKA
a
Department of Organic Chemistry, Faculty of Science, Charles University,
Hlavova 2030, 128 40 Prague 2, Czech Republic; e-mail: dzoganova@gmail.com,
mila@natur.cuni.cz, trnka@natur.cuni.cz
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
Flemingovo nám. 2, 166 10 Prague 6, Czech Republic; e-mail: budesinsky@uochb.cas.cz,
dracinsky@uochb.cas.cz
1
2
3
b
1
2
Received August 23, 2006
Accepted Septem ber 23, 2006
Dedicated to Professor Antonín Holý on the occasion of his 70th birthday.
Epoxide or pseudo-epoxide m igration of 1,6:2,3-dian h ydro- an d 1,6:3,4-dian h ydro-β-D-h exo-
pyran oses was effected by treatm en t with aqueous sodium h ydroxide or sodium iodide in
aceton e to give equilibrium m ixtures. Various iodo derivatives of 1,6-an h ydro-β-D-h exo-
pyran oses were prepared as poten tial in term ediates for pseudo-epoxide m igration . NMR was
used for followin g th e reaction m ech an ism of epoxide an d pseudo-epoxide m igration s an d
an alysis of reaction m ixtures. Experim en tal data were com pared with DFT calculation s.
Ch air–boat equilibration of 1,6-an h ydro-3-deoxy-3-h alo-β-D-glucopyran oses was discussed.
Keyw ord s: Carboh ydrates; An h ydro sugars; Epoxides; Epoxide m igration ; Pseudo-epoxide
m igration ; NMR spectroscopy; DFT calculation s; Con form ation an alysis.
Epoxide m igration 1, also called Payn e rearran gem en t2,3 is a well-kn own
ph en om en on related to α-h ydroxy epoxides wh ich , un der favorable steric
con dition s, un dergo isom erization in alkalin e solution at room tem perature
to give an equilibrium m ixture of two isom eric α-h ydroxy epoxides. Th is
rearran gem en t was first observed by Newth 1 an d was later studied in de-
tail4,5 with 1,6:2,3-dian h ydro-β-D-m an n opyran ose4 (1) an d 1,6:3,4-di-
an h ydro-β-D-galactopyran ose5 (2) wh ich are con verted in to 1,6:3,4-di-
an h ydro-β-D-altropyran ose (3) an d 1,6:2,3-dian h ydro-β-D-gulopyran ose (4),
respectively (Sch em es 1 an d 2). Several auth ors in vestigated also m igration
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515
© 2006 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20061497

1498
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
of oth er sugar epoxides6–12 an d in ositol epoxides13 (see also review1c) sin ce
th ese epoxides are readily available, an d th erefore valuable startin g m aterial
for organ ic syn th esis.
SCHEME 1
SCHEME 2
An oth er type of isom erization , so called pseudo-epoxide m igration 1c, was
first m en tion ed by Elbert et al.14 with 1,6:2,3-dian h ydro-β-D-allopyran ose (5)
an d 1,6:3,4-dian h ydro-β-D-allopyran ose (6). Th is reaction was catalyzed by
th e action of sodium iodide in aceton e at elevated tem perature (Sch em e 3).
However, detailed experim en tal data are n ot available. As predicted, base-
catalyzed epoxide-m igration con dition s are n ot effective in pseudo-epoxide
m igration (see below).
SCHEME 3
We presen t h ere our study of epoxide an d pseudo-epoxide m igration of
all eigh t possible 1,6:2,3- an d 1,6:3,4-dian h ydro-β-D-h exopyran oses usin g
m ain ly NMR spectroscopy for exam in in g th e reaction course in m ore detail.
Startin g dian h ydroh exoses 1–8 were prepared from 1,6-an h ydro-β-D-gluco-
pyran ose accordin g to th e followin g literature: D-m an n o-4,15 (1), D-altro-4,15
(3), D-galacto-5,16 (2), D-gulo-5 (4), D-allo-17 (5, 6), D-talo-18,19 (7, 8).
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1499
Epoxide m igration of dian h ydroh exoses 1–4 was in vestigated at am bien t
tem perature (20–25 °C) in D2O solution s con tain in g NaOD. Equilibria were
ach ieved startin g from all pure isom ers with in several h ours (Sch em es 1
an d 2). As expected, epoxides 5, 6, an d 8 did n ot sh ow an y ch an ge with in
24 h un der th e sam e reaction con dition s. Con versely, wh en epoxide 7 was
subjected to th e sam e con dition s, a slow steadily in creasin g con version to
th e kn own 20 1,6-an h ydro-3-deoxy-β-D-threo-h exopyran os-4-ulose (9) was
observed (Sch em e 4).
SCHEME 4
Pseudo-epoxide m igration of allo-epoxides 5 and 6 was perform ed at 100 °C
in aceton e or h exadeuterated aceton e solution of sodium iodide to give
with in 24 h an equilibrium m ixture con tain in g epoxides 5 an d 6 in th e
26:74 ratio (Sch em e 3). It is worth m en tion in g th at th e pseudo-epoxide
m igration also occurs with 1,6:2,3- (7) an d 1,6:3,4-dian h ydro-β-D-talo-
pyran ose (8) (Sch em e 5). Neverth eless, th e rate of th is reaction is m arkedly
slower com pared to th e reaction rate of allo-epoxides 5 an d 6, an d a sign ifi-
can t am oun t of 1,6-an h ydro-3-deoxy-3-iodo-β-D-idopyran ose (10) is con tin -
ually form ed. Th us, an equilibrium m ixture was n ot reach ed an d on ly th e
com position of th e reaction m ixture in dicates th e tren d of th e isom er-
isation . Th e treatm en t of 10 with aqueous NaOD gave on ly sm all am oun ts
SCHEME 5
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1500
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
of talo-epoxides 7 an d 8. However, wh en water was replaced with aceton e,
a rapid reaction took place an d epoxides 7 an d 8 were form ed in th e 20:80
ratio.
Th e epoxide-m igration m ech an ism of epoxides 1–4 is un derstood as an
in tram olecular SN2 reaction of th e deproton ated α-h ydroxy group attackin g
th e adjacen t oxiran e rin g. Possible cooperation of Na+ in th e cleavage of th e
oxiran e rin g by I– in aceton e can n ot be excluded. Th is follows from th e fact
th at th e pseudo-epoxide m igration proceeded slower in an aqueous or
dim eth ylform am ide solution . On th e oth er h an d, a plausible m ech an ism of
th e pseudo-epoxide m igration of epoxides 5–8 is a two-step process in volv-
in g in term ediates, poten tially deproton ated deoxy iodo derivatives of th e
correspon din g 1,6-an h ydro-β-D-h exopyran oses.
SCHEME 6
In order to iden tify th ese in term ediates, we prepared 1,6-an h ydro-
3-deoxy-3-iodo-β-D-glucopyran ose (11) by oxiran e-rin g cleavage in 1,6:2,3-
dian h ydro-β-D-allopyran ose (5) with h ydrogen iodide in dioxan e at room
tem perature (Sch em e 6). In a sim ilar way, 1,6-an h ydro-2-deoxy-2-iodo-
β-D-galactopyran ose (12) an d iodo derivative 10 were form ed from talo-
epoxide 7, but th e iodo derivative 12 was n ot isolated (Sch em e 7).
1,6-An h ydro-3-deoxy-3-iodo-β-D-m an n opyran ose (13) was prepared from
SCHEME 7
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1501
altro-epoxide 3 (Sch em e 8). Iodo derivatives 10–13 were con verted in to
th e correspon din g epoxides (1,6:2,3- an d 1,6:3,4-dian h ydro-β-D-h exo-
pyran oses) by treatm en t with NaOH in aqueous or aceton e solution
(Sch em es 6–8).
SCHEME 8
Treatm en t of th e iodo derivative 11 with a dilute aqueous sodium
h ydroxide solution at room tem perature resulted in th e form ation of a
m ixture of both allo-epoxides 5 an d 6 in th e 21:79 ratio, respectively
(Sch em e 6). Th is is in acceptable agreem en t with th e result of th e pseudo-
epoxide m igration of allo-epoxides 5 an d 6 by th e action of sodium iodide
(Sch em e 3). Even th ough th e presen ce of 11 in th e reaction m ixture was
n ot observed durin g th e isom erization , th is is n ot out of keepin g with th e
suggested m ech an ism in volvin g th e deproton ated form of th e iodo deriva-
tive 11 as a reaction in term ediate.
A sim ilar m ixture of allo-epoxides 5 an d 6 is form ed21 by th e treatm en t
of 1,6-an h ydro-3-O-tosyl-β-D-glucopyran ose an d its 2,4-diben zoate17 with
sodium m eth oxide, or by deam in ation of 3-am in o-1,6-an h ydro-3-deoxy-
β-D-glucopyran ose with n itrous acid14
.
In con n ection with th e above described pseudo-epoxide m igration of
allo-epoxides 5 an d 6 con trolled by th e sodium iodide catalysis, we were in -
terested in determ in in g wh eth er th is catalyst was also effective in th e
epoxide m igration . Th us, we treated manno-epoxide 1 with sodium iodide
in aceton e un der th e sam e reaction con dition s. A typical product of th e
epoxide m igration , altro-epoxide 3, was foun d in th e reaction m ixture to-
geth er with th e startin g manno-epoxide 1 an d a sm all am oun t of 3-deoxy-
3-iodo-β-D-altropyran ose (14) (Sch em e 9). Th e form ation of altro-epoxide 3
m ay be ration alized by th e effect of base catalysis of th e iodide an ion in an
aprotic solven t such as aceton e. However, a sim ilar reaction with gulo-
epoxide 4 did n ot proceed.
Th e above m en tion ed differen t beh avior of allo- an d talo-epoxides 5, 6
an d 7, 8, respectively, in th e reaction with an aceton e solution of sodium
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1502
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
iodide can possibly be accoun ted for on th e basis of con form ation al con sid-
eration s. Wh en th e oxiran e-rin g cleavage takes place accordin g to th e
Fürst–Plattn er rules (trans-diaxial oxiran e-rin g cleavage), th e resultin g iodo
derivatives (an d th eir correspon din g oxide ion s) are readily form ed. Th ese
in term ediates are also pron e to regen erate prom ptly startin g epoxides or, if
it is sterically favored, th e correspon din g isom eric epoxides. Th is is th e case
of allo-epoxides 5 an d 6 wh ere th e attackin g iodide ion open s th e oxiran e
rin g at C-3 to give oxide ion derived from iodo derivative 11 (Sch em e 3).
An altern ative attack of th e iodide ion at position s C-2 or C-4 is sterically
h in dered by th e 1,6-an h ydride bon d, an d is con form ation ally disfavored.
On th e oth er h an d, talo-epoxides 7 an d 8 are preferen tially attacked at C-2
or C-4 to give diaxial 2-iodo- an d 4-iodo derivatives, respectively. However,
both th ese iodo derivatives are expected to give th e startin g epoxides. Th e
approach of th e iodide ion to position C-3 in talo-epoxides 7 an d 8 is n ot
h in dered; n everth eless, th e diequatorial cleavage of th e oxiran e rin g is
expectably slow an d th e resultin g 3-iodo derivative 10 is relatively stable to
be iden tified in th e reaction m ixture (Sch em e 5). Th e form ation of 1,6:2,3-
an d 1,6:3,4-dian h ydro-β-D-talopyran oses 7 an d 8 from 3-iodo derivative 10
requires an an tiplan ar orien tation of th e oxide ion an d leavin g iodide
group wh ich is realised in BO,3 con form ation . Th e passin g-by effect plays an
im portan t role in th is in tercon version an d con sequen tly, disfavors th e ac-
com plish m en t of th e reaction 7.
SCHEME 9
Th e structure of iodo derivatives 10 an d 14 (see Sch em es 5–9) foun d in
th e reaction m ixtures was proved by NMR m easurem en ts, see below, an d by
con vertin g each am on g th em in to th e correspon din g epoxides 7, 8 an d 1,
3, respectively. In addition to iodo derivative 11, th e correspon din g ch loro
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1503
an d brom o derivatives 15 an d 16 were prepared by treatm en t of allo-epoxide
5 with h ydrogen ch loride an d h ydrogen brom ide, respectively. Th eir ch air–
boat population s were calculated an d com pared with fluoro derivative 17.
NMR SPECTRA AND THEORETICAL CALCULATIONS
NMR Characterization of Prepared Iodo Derivatives
Th e structures of th e prepared iodo derivatives 10–14 were con firm ed by
1H an d 13C NMR spectra (Tables I–III). Th e presen ce an d position of iodin e
atom is n ot well in dicated in 1H NMR spectra but is clearly m an ifested by
ch aracteristic upfield sh ifts of carbon atom bearin g iodin e (δ 22–38). Vici-
n al proton couplin g J(2,3) in 12 an d 14, J(3,4) in 13 an d both J(2,3) an d
J(3,4) in 10 an d 11 are sen sitive to th e population s of ch air an d boat form s
of pyran ose rin g. Usin g of th e observed J-values an d th e gen eralized Karplus
equation 22 sh ows th e h igh preferen ce (80–97%) of a ch air form in all pre-
pared iodo derivatives 10–14.
Conversion of Iodo Derivatives to Epoxides in Alkaline Water Solution
About 5 m g of an iodo derivative 10–14 was dissolved in D2O (0.5 m l) an d
1
its H NMR spectrum recorded. Th e ch em ical sh ifts an d couplin g con stan ts
are sum m arized in Tables I an d II. Th en on e drop of 10% NaOD in D2O was
1
added an d H NMR spectra were recorded after 48 h stan din g at room tem -
perature. In th e case of com poun d 10 th e con version was ach ieved on ly in
aceton e-d6 solution with NaOD. Th e structure an d relative am oun ts of th e
presen t com pon en ts were determ in ed by detailed an alysis of NMR spectra.
Results are discussed in th eoretical part an d sum m arized in Sch em es 5–9.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1504
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
TABLE I
1H NMR ch em ical sh ifts of com poun ds 1–16
Com pd Solven t
H-1
H-2
H-3
H-4
H-5
H-6en
H-6ex
OH
–
1
2
3
4
5
6
7
8
9
D2O
5.83
3.64
3.44
3.83
3.64
3.90
3.67
3.26
2.95
3.285
3.16
3.74
3.68
3.76
3.535
3.96
3.87
4.16
3.24
3.085
3.24
3.035
3.12
2.88
3.21
3.01
3.50
3.45
3.43
3.35
3.45
3.24
3.43
3.33
2.95
2.31
4.06
3.93
3.82
3.63
3.45
3.20
4.25
4.175
3.90
3.93
3.47
3.43
4.35
4.24
3.94
3.86
–
4.52
4.43
5.03
4.895
4.87
4.71
4.51
4.41
4.47
4.46
4.86
4.81
4.53
4.38
5.01
4.95
4.50
3.74
3.64
3.98
3.87
4.17
4.07
4.16
4.14
3.805
3.805
4.09
4.06
3.99
4.05
3.96
3.94
3.97
3.74
3.60
3.55
3.43
3.885
3.78
3.85
3.68
3.92
3.87
3.78
3.73
3.63
3.465
3.58
3.48
3.94
(CD3)2CO 5.67
D2O 5.29
(CD3)2CO 5.11
D2O 5.365
(CD3)2CO 5.21
D2O 5.70
(CD3)2CO 5.51
D2O 5.71
(CD3)2CO 5.61
D2O 5.255
(CD3)2CO 5.18
D2O 5.81
(CD3)2CO 5.625
D2O 5.35
(CD3)2CO 5.26
–
2-OH: 4.60
–
2-OH: 4.04
–
4-OH: 4.90
–
–
–
–
CDCl3
5.59
2-OH: 2.07
2-OH: 2.08;
4-OH:2.36
CDCl3
10
11
5.24
5.27
5.48
5.47
3.83
3.88
4.07
3.80
3.77
4.04
4.13
4.14
4.12
4.41
4.485
4.58
4.06
4.055
4.48
3.75
3.76
3.85
D2O
–
2-OH: 2.90;
4-OH:2.90
CDCl3
D2O
4.035
4.05
3.87
4.08
4.17
4.19
4.65
4.62
4.28
4.37
3.81
3.72
–
(CD3)2CO 5.37
3-OH: 2.94;
4-OH:2.99
CDCl3
12
13
5.61
5.70
5.43
5.45
4.25
4.26
3.15
4.29
4.38
4.55
4.37
4.41
4.38
4.48
4.53
4.53
4.36
4.47
4.51
3.73
3.74
3.87
D2O
–
2-OH: 2.32;
4-OH:2.80
CDCl3
D2O
3.33
3.88
3.81
3.77
4.455
4.36
3.63
3.84
4.54
3.97
3.81
3.94
4.63
4.61
4.55
4.55
4.58
3.915
4.09
4.13
3.86
3.73
3.70
3.70
–
14
15
16
(CD3)2CO 5.35
(CD3)2CO 5.32
(CD3)2CO 5.32
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1505
TABLE II
1H NMR couplin g con stan ts of com poun ds 1–16
Co-
m pd
6en ,
6ex
Solven t
1,2 2,3 3,4 4,5 5,6en 5,6ex 1,3 1,5 1,6en 1,6ex 2,4 3,5 4,6ex
a
i
i
1a D2O
3.2 3.9 0.8 1.3
0.6
0.5
0.5
0.5
0.6
0.4
0.5
0.5
<0.3
0.85 1.6
0.9 1.5
0.9 0.7
0.9 ≤0.5
0.9 0.7
1.0 0.7
1.0 2.1 0.8
1.0 2.1 0.8
2.0
(CD3)2CO 7.1 3.2 3.8 0.7 1.2 2.15
6.6
4.8
4.9
4.6
4.5
6.3
6.2
6.8
6.7
4.6
4.5
6.2
6.2
4.9
4.7
4.9
2b D2O
7.0 1.1 0.7 4.15 5.0 0.7
1.6
(CD3)2CO 6.4 1.0 ≤0.5 4.3 5.0 0.8
1.5
3c D2O
(CD3)2CO 7.4 3.1
D2O
(CD3)2CO 7.9 1.0 3.9
D2O
(CD3)2CO 8.2 1.3 4.0 4.8 1.1 2.4
D2O 7.7 0.9 4.5 4.3 1.8 0.7
(CD3)2CO 7.5 0.7 4.8 4.1 1.7 0.7
D2O 7.6 3.0 4.25 3.1 6.2 1.65
(CD3)2CO 6.9 3.0 4.1 3.0 6.0 1.7
D2O 7.0 3.8 3.5 4.5 4.7 0.75
(CD3)2CO 6.6 3.8 3.5 4.35 4.7 0.7
7.8 3.05
0
0
4.1 1.7 0.8
4.0 1.6 0.7
2.3 0.6
2.3 0.55 ≤0.5
0.7 0.4 0.65
0.6 0.4 0.6
4
5
6
7
8
8.5 1.2 4.0
0
0
5.25 2.1
5.3 2.1
<0.3
~0.3
0.45
0.5
8.45 1.3 4.15 4.9 1.0 2.3
0.7
0.55
0.5
0.75
1.9
2.1 0.6 <0.3
<0.3
~0.4
0.5
0.8
2.1
~0.4
0.5
0.75 0.4
1.0 0.6
1.0 0.6
0.6
0.6
1.2
0.5
0.6
1.2
0.6
9d CDCl3
8.4 2.8 7.0
7.7
–
–
1.5
1.0 0.4
1.6
10e CDCl3
D2O
11f CDCl3
8.1 1.5 9.0 9.0 4.1 0.5
8.3 1.8 9.7 9.95 4.1 1.0
8.0 1.8 2.4 2.6 1.9 0.9
8.1 1.2 4.6 4.6 1.5 1.1
5.0
5.0
5.4
5.55
5.4
4.8
5.2
5.4
5.6
5.4
5.5
5.4
0.8
1.0
0.3
0.5
0.5
0.5
0.4
0.5
0.4
0.3
1.2 0.3 0.3
1.0 1.6
1.0
D2O
0.9
0.3
(CD3)2sCO 7.9 1.6 3.3 3.3 1.75 1.0
12g CDCl3
1.0
0.8 1.3
0.6 1.2 1.1
0.5 1.3 1.2
0.9 1.6
0.9 1.5
7.8 1.4 1.4 5.0 4.2 0.7
7.7 1.5 1.3 4.8 4.0 0.7
8.1 2.2 6.1 2.4 1.9 0.8
8.3 1.95 6.35 1.9 1.8 0.9
1.3 0.4
1.2
D2O
13h CDCl3
D2O
0.4
1.0 0.3
1.0
14
15
16
(CD3)2CO 8.1 1.6 10.3 4.1 2.5 0.9
(CD3)2CO 7.7 1.0 4.0 4.2 1.6 1.0
(CD3)2CO 7.6 1.2 4.65 4.8 1.45 1.0
0.8
0.8
0.3
0.5
0.8 1.1
0.5 0.9
a
b
c
d
e
J(1,4) = 0.7. J(2,OH) = 6.6. J(2,OH) = 9.3. J(2,OH) = 9.9, J(3eq,3ax) = 17.2. J(2,OH) =
f
g
7.3, J(4,OH) = 3.2. J(1,4) = 0.6, J(2,5) = 0.5. J(3,OH) = 7.5, J(4,OH) = 8.8, J(2,5) = 0.7.
h
i
J(2,OH) = 11.4, J(4,OH) = 9.0, J(1,4) = 0.5. Couplin g con stan ts could n ot be resolved.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1506
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
1
Epoxide Migration in Alkaline Water Solution Followed by H NMR
1
About 5 m g of an epoxide 1–8 was dissolved in D2O (0.5 m l) an d its H NMR
spectrum recorded. Proton ch em ical sh ifts an d couplin g con stan ts are sum -
m arized in Tables I an d II. Th en 1 drop of 10% NaOD in D2O was added
an d 1H NMR spectra were recorded repeatedly at defin ed tim e in tervals
durin g 3 days stan din g at room tem perature. Th e structure an d relative
am oun ts of presen t com pon en ts were determ in ed from th e detailed an aly-
sis of NMR spectra. Results are discussed in th eoretical part an d sum m arized
in Sch em es 1, 2, an d 4.
Reaction of Epoxides in Acetone with Sodium Iodide
(Pseudo-Epoxide Migration)
Th e each epoxide 1, 4, 5, 7, an d 8 was dissolved in aceton e, fresh ly pow-
dered NaI (1.5–1.8 eq.) was added an d h eated to 100 °C in sealed am pule.
After 24 h h eatin g th e NMR spectrum was recorded an d th e structure an d
relative am oun ts of presen t com pon en ts were determ in ed from th e detailed
an alysis of NMR spectrum . In som e cases a m uch lon ger h eatin g was used.
To th e reaction m ixtures of epoxide 1, 7, an d 8, wh ere som e am oun t of
iodo derivative was presen t, 1 drop of 30% NaOD in D2O was added an d
NMR spectrum recorded. Results are discussed in th eoretical part an d sum -
m arized in Sch em es 5–9.
TABLE III
13C NMR ch em ical sh ifts of com poun ds 9–16
Com pd
Solven t
C-1
C-2
C-3
C-4
C-5
C-6
2
3
(CD3)2CO
(CD3)2CO
CDCl3
101.82
100.38
101.33
101.00
101.90
103.82
102.03
101.66
103.40
103.68
103.88
66.68
66.62
69.56
76.96
73.78
74.93
27.38
65.43
74.20
74.32
75.14
50.60
51.81
43.15
38.05
22.77
26.64
73.74
34.74
36.85
62.27
53.95
53.34
72.59
70.60
77.93
75.07
77.07
79.11
75.50
76.93
77.19
78.28
78.66
65.01
57.80
66.77
64.79
66.38
67.77
65.21
67.00
66.64
66.93
67.32
50.75
202.52
73.96
73.31
74.18
62.73
74.73
72.19
74.03
74.62
9
10
11
CDCl3
CDCl3
(CD3)2CO
CDCl3
12
13
14
15
16
CDCl3
(CD3)2CO
(CD3)2CO
(CD3)2CO
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1507
Theoretical Calculations of Isomeric Epoxides Population in
Equilibrium Mixtures
Th e population s of isom eric epoxides in equilibrium m ixtures, determ in ed
from NMR spectra, are sum m arized in Table IV. Th ey sh ould correspon d to
th e free en ergy differen ce ∆G between pair of epoxides. Th erefore we h ave
tried to estim ate th ose population s usin g th eoretical calculation s of th e en -
ergy of in dividual epoxides 1–8 by: (1) sim ple m olecular m ech an ics (MM+
force field)23 an d (2) ab in itio calculation (DFT m eth od with B3LYP/6-31**
basis set)24. Th e geom etry of each staggered OH-rotam er was obtain ed by
en ergy m in im ization . Th e values of th e lowest en ergy OH-rotam ers are in
bold an d th ose wh ich can form in tram olecular H-bon ds are un derlin ed.
Th e search for en ergy m in im a for OH staggered rotam ers usin g DFT m eth od
led in som e cases to th e result th at th e expected rotam er was n ot foun d an d
th e optim ization en ded with th e geom etry correspon din g to an oth er
rotam er (see arrows in Table IV). Th e vibration an d th erm och em ical an aly-
sis was m ade for all optim ized rotam er structures th at allowed to obtain
values of Gibbs en ergy G. For calculation of th e th eoretical population of
isom eric epoxide pairs, th ree attem pts were used: (A) en ergy differen ce be-
tween th e calculated lowest en ergy rotam ers, (B) all calculated staggered
OH-rotam ers taken with population s calculated from th eir relative en ergy
values, (C) en ergy differen ces between trans-OH rotam ers (n ot able to form
in tram olecular H-bon ds) were used.
(1) MM+ results: All th ree attem pts (A–C) provided very sim ilar results
an d correct prevailin g epoxide in pairs 1 3 an d 2 4, but th e opposite
prevailin g rotam er th an NMR experim en t in pairs 5 6 an d 7 8 (see
Table IV). It seem s obvious th at sim ple MM+ force-field fails in th is type of
application . Th erefore we h ave turn ed our atten tion to h igh er level of th eo-
retical calculation s based on th e DFT m eth od.
(2) DFT results: Th e approach es (A) an d (B) sh ow rath er sim ilar results
an d give righ t prevailin g epoxide in pairs 1 3, 5 6 an d 7 8 but th e
wron g on e in 2 4. It is on ly attem pt (C) based on com parison of trans-
OH-rotam ers th at predicts righ t prevailin g epoxide in all four pairs (see Ta-
ble IV). Th is could be explain ed by th e fact th at solvation in a water solu-
tion destabilizes th e OH-rotam ers wh ich can form in tram olecular H-bon ds
an d con sequen tly, trans-OH-rotam ers (m ost easily accessible to form in ter-
m olecular H-bon ds with water) are m ost stable.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1508
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1509
Conformation of Pyranose Ring in 1,6-Anhydro-β-D-Glucopyranose with
Halogen Atom (F, Cl, Br, I) in Position 3
To estim ate th e effect of th e type of h alogen atom in position 3 on th e con -
form ation of pyran ose rin g in 3-h alogluco derivatives we h ave syn th esized,
in addition to 3-iodo derivative 11, also 3-ch loro an d 3-brom o derivatives
15 an d 16. Th eir NMR spectra were m easured in (CD3)2CO (for data see
Tables I–III) to be fully com parable with partial NMR data for 3-fluoro
derivative 17 described by Grin dley25
.
Th e con form ation of pyran ose rin g in 1,6-an h ydro-β-D-glucopyran ose
derivatives is well reflected by vicin al couplin g con stan ts J(2,3) an d J(3,4).
In gen eral, h igh er J-values in dicate in creasin g population of th e boat form .
However, th e differen ces in th e observed J-values in our series of h alogen o
derivatives are in fluen ced n ot on ly by th e population s of th e ch air an d boat
form but also differen t electron egativities of h alogen atom s an d by solven t.
Th erefore we calculated first th e expected J-values for th e ch air an d boat
form of each h alo derivative usin g gen eralized Karplus equation 22 an d
torsion an gles for ch air an d boat form derived by Grin dley25 (Table V). Th e
calculated J(ch air) an d J(boat) values an d th e observed averaged J(2,3) an d
J(3,4) values were used for estim ation of th e equilibrium population of th e
ch air form (X(ch air)) usin g sim ple relation :
X(ch air) = (J(observed) – J(boat))/(J(ch air) – J(boat)).
Th e results sum m arized in Table V sh ow th at th e population of th e ch air
form decreases with th e bulkin ess of h alogen substituen t: from fluoro (97%
ch air), to ch loro (62% ch air) an d brom o derivative (55% ch air) wh ile it
in creases again for iodo derivative (74% ch air). It seem s th at in th e case of
3-iodo derivative gauche in teraction s between OH an d bulky iodin e atom
can destabilize th e boat form an d lead to h igh er population of th e ch air
form th an in ch loro an d brom o derivative. Th e effect of solven t can be
dem on strated on 3-iodo derivative wh ich gives J(2,3) = 2.4 an d J(3,4) =
2.6 Hz in CDCl3, 3.3 Hz for both in (CD3)2CO an d 4.6 Hz for both in D2O.
Accordin g to th ese J-values, th e calculated am oun t of ch air form decreases
from 84% in CDCl3 to 74% in (CD3)2CO an d 59% in D2O.
Th e above discussed ch air–boat equilibrium of pyran ose rin g in h alo de-
rivatives 11, 15–17 is determ in ed by free en ergy of both con form ers. Th ere-
fore we h ave tried to calculate correspon din g en ergy values an d com pare
th e results with th ose obtain ed from J(H,H)’s.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1510
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1511
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1512
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
Th e presen ce of two OH groups in th ese derivatives leads to n in e com bi-
n ation s of possible staggered OH-rotam ers. Th e geom etry of each rotam er
was obtain ed by en ergy m in im ization usin g m olecular m ech an ics (MM+)23.
It was th en used as th e startin g geom etry for geom etry optim ization by
th e ab in itio DFT m eth od24 with B3LYP/6-311+g** for F, Cl an d Br deriva-
tives an d B3LYP/3-21g** for I derivative. In som e cases (in dicated by a in
Table VI) th e en ergy m in im um of given rotam er was n ot foun d an d optim i-
zation resulted in th e geom etry th at correspon ds to an oth er rotam er. Th e
population of each ch air- an d boat-form rotam er was calculated from its
en ergy an d th eir sum was used to estim ate th e fin al ch air an d boat popula-
tion . Th e calculated ch air–boat equilibrium population s agree very well
with th ose calculated from th e observed averaged J(2,3) an d J(3,4) values
except for 3-iodogluco derivative 11. It can be due to th e lower accuracy of
geom etry optim ization an d en ergy calculated with B3LYP/3-21g** (h igh er
basis set is n ot defin ed for iodin e atom ) an d/or to th e effect of solvation
th at is n ot presen t in th e calculation .
EXPERIMENTAL
Meltin g poin ts were determ in ed with Boëtius m icro m eltin g-poin t apparatus an d are un cor-
rected. Th e optical rotation s were m easured on an Autopol III (Rudolph Research , Flan ders
(NJ), U.S.A.) polarim eter at 25 °C, [α]D values are given in 10–1 deg cm 2 g–1. NMR spectra
were m easured on a Bruker AVANCE-500 and/or Varian UNITY-500 instrum ent (1H at 500 MHz;
13C at 125.7 MHz) in CDCl3 (1H referen ced to TMS; 13C to solven t peak usin g δC(CDCl3)
77.0), D2O an d/or D2O + NaOD (a drop of dioxan e added an d used as referen ce: δH 3.76,
δC 69.33) an d (CD3)2CO (referen ced to th e solven t peak: δH 2.09; δC 30.7). Th e structures of
all syn th esized com poun ds 1–16 were con firm ed by 1H an d 13C NMR spectra. Structural
assign m en t of proton sign als was obtain ed usin g H,H-COSY spectra, ch aracteristic splittin g
pattern s an d ch em ical sh ifts. Couplin g con stan ts were derived from expan ded resolution en -
h an ced spectra. Hom on uclear decouplin g experim en ts were used to determ in e th e values of
som e sm all couplin g con stan ts. Carbon sign als were assign ed from APT an d 2D-H,C-HSQC
spectra. Reaction s were m on itored by th in -layer ch rom atograph y (TLC) on Merck silica gel
60 F254 plates an d visualized un der UV ligh t (254 n m ) an d/or by carbon ization at h igh tem -
perature. All solven ts were dried an d distilled; aceton e with K2CO3, dioxan e with LiAlH4,
ch loroform with P2O5. Solven ts were evaporated usin g vacuum rotary evaporator (water
bath 45 °C). Th e sam ples for an alysis were dried at 6.5 Pa at room tem perature.
Isom erization of Epoxides by Sodium Iodide.
Gen eral Procedure
A solution of epoxide an d sodium iodide in dry aceton e or aceton e-d6 was sealed in to a glass
am pule an d h eated at 100 °C for a given tim e. Th en , th e reaction m ixture was cooled down
to room tem perature. Th e com position of th e reaction m ixture was determ in ated by NMR
m easurem en t, in case of used dry aceton e th e solven t was first evaporated.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

Epoxide and Pseudo-Epoxide Migration
1513
Isom erization of 1,6:2,3-Dian h ydro-β-D-m an n opyran ose (1)
Epoxide4,15 1 (8.8 m g, 0.06 m m ol) an d NaI (16.4 m g, 0.11 m m ol) in dry aceton e (0.4 m l);
1-h h eatin g. Th e determ in ed com position of th e reaction m ixture was 1:3:14 = 26:66:8.
Isom erization of 1,6:3,4-Dian h ydro-β-D-galactopyran ose (2)
Epoxide5,16 2 (7.9 m g, 0.05 m m ol) an d NaI (12.1 m g, 0.08 m m ol) in dry aceton e (0.8 m l).
No reaction was observed after 24-h h eatin g.
Isom erization of 1,6:2,3-Dian h ydro-β-D-gulopyran ose (4)
Epoxide5 4 (8.3 m g, 0.06 m m ol) an d NaI (16 m g, 0.08 m m ol) in aceton e-d6 (0.8 m l). No
reaction was observed after 4-day h eatin g.
Isom erization of 1,6:2,3-Dian h ydro-β-D-allopyran ose (5)
Epoxide17 5 (7.6 m g, 0.05 m m ol) an d NaI (11.8 m g, 0.08 m m ol) in aceton e-d6 (0.8 m l);
24-h h eatin g. Th e determ in ed com position of th e reaction m ixture was 5:6 = 24:76.
Isom erization of 1,6:2,3-Dian h ydro-β-D-talopyran ose (7)
Epoxide18,19 7 (10.5 m g, 0.07 m m ol) an d NaI (16.8 m g, 0.11 m m ol) in aceton e-d6 (1.1 m l).
Th e determ in ed com position of th e reaction m ixture was 7:8:10 = 53:42:5 after 8-day h eat-
in g an d 7:8:10:un iden tified products = 15:10:67:8 after 19-day h eatin g.
Isom erization of 1,6:3,4-Dian h ydro-β-D-talopyran ose (8)
Epoxide18,19 8 (9.6 m g, 0.07 m m ol) an d NaI (14.9 m g, 0.1 m m ol) in aceton e-d6 (1.1 m l). Th e
determ in ed com position of th e reaction m ixture was 7:8:10:un iden tified product = 11:79:7:3
after 8-day h eatin g an d 7:8:10:un iden tified product = 15:45:32:8 after 19-day h eatin g.
Epoxide Migration of 1,6:2,3-Dian h ydro-β-D-talopyran ose (7)
in Alkalin e Water Solution
Epoxide18,19 7 (200 m g, 1.39 m m ol) was dissolved in 4.3 m l D2O an d 0.6 m l of 30% NaOD
in D2O was added. Th e reaction m ixture was allowed to stan d at room tem perature for 12 days.
Alkalin e solution was th en n eutralized with cooled 1 M HCl solution (2.5 m l, un til pH 8)
an d with acetic acid (1 drop, un til pH 7) an d lyoph ilized. Extract from CDCl3 was used for
NMR m easurem en t an d th e com position of th e reaction m ixture was determ in ed as 7:9 =
40:60.
Syn th esis of 1,6-An h ydro-3-deoxy-3-iodo-β-D-h exopyran oses.
Gen eral Procedure
Dian h ydroh exopyran ose was dissolved in dry dioxan e an d th e solution of 9% HI in ch loro-
form was added. Th e reaction m ixture was allowed to stan d at room tem perature for a given
tim e, diluted with dich lorom eth an e (20 m l), extracted with water (3 × 20 m l) an d th e
aqueous layer was evaporated. Th e residue was ch rom atograph ed on a silica gel colum n in
toluen e–EtOAc (3:1).
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 10, pp. 1497–1515

1514
Džoganová, Černý, Buděšínský, Dračínský, Trnka:
1,6-An h ydro-3-deoxy-3-iodo-β-D-idopyran ose (10)
Prepared from epoxide18,19 7 (0.5 g, 3.5 m m ol) in dioxan e (20 m l) an d HI solution (3.9 m l)
followin g th e gen eral procedure (stan din g overn igh t). Yield 150 m g (16%) of 10; m .p.
125–126 °C; [α]D –73 (c 0.35, MeOH). For C6H9IO4 (272.0) calculated: 26.49% C, 3.33% H,
46.65% I; foun d: 26.57% C, 3.34% H, 46.36% I. Th e rest of th e reaction m ixture con tain in g
th e iodo derivative 12 an d th e startin g epoxide 7 (200 m g, 55:45) was n ot separated.
1,6-An h ydro-3-deoxy-3-iodo-β-D-glucopyran ose (11)
Prepared from epoxide17 5 (0.2 g, 1.4 m m ol) in dioxan e (10 m l) an d HI solution (1.4 m l)
followin g th e gen eral procedure (10-m in stan din g). Yield 0.33 g (89%) of 11 as a colorless
oil; [α]D –64 (c 0.15, H2O). For C6H9IO4 (272.0) calculated: 26.49% C, 3.33% H, 46.65% I;
foun d: 26.54% C, 3.64% H, 46.29% I.
1,6-An h ydro-3-deoxy-3-iodo-β-D-m an n opyran ose (13)
Prepared from epoxide4,15 3 (0.2 g, 1.4 m m ol) in dioxan e (10 m l) an d HI solution (1.4 m l)
followin g th e gen eral procedure (10-m in stan din g). Yield 0.37 g (97%) of 13; m .p. 128.5–
130.5 °C; [α]D –121 (c 0.36, H2O). For C6H9IO4 (272.0) calculated: 26.49% C, 3.33% H,
46.65% I; foun d: 26.75% C, 3.41% H, 46.35% I.
1,6-An h ydro-3-ch loro-3-deoxy-β-D-glucopyran ose (15)
Epoxide17 5 (29 m g, 0.2 m m ol) was dissolved in dry dioxan e (1.5 m l) an d 5.18 M solution of
HCl in dioxan e (0.2 m l) was added. Th e reaction m ixture was allowed to stan d at room tem -
perature for 20 h . After evaporation of th e solven t th e residue was diluted with ch loroform
(10 m l), extracted with water (3 × 10 m l) an d th e aqueous layer was evaporated to give 27 m g
(75%) of com poun d 15 as a wh ite solid; m .p. 49–51 °C; [α]D –83 (c 0.34, H2O). For C6H9ClO4
(180.0) calculated: 39.91% C, 5.02% H, 19.63% Cl; foun d: 39.98% C, 5.13% H, 19.70% Cl.
1,6-An h ydro-3-brom o-3-deoxy-β-D-glucopyran ose (16)
To a solution of epoxide17 5 (29 m g, 0.2 m m ol) in dry dioxan e (1.5 m l) a saturated solution
of HBr in dich lorom eth an e (0.1 m l) was added an d th e reaction m ixture was allowed to
stan d overn igh t at room tem perature. TLC sh owed residual epoxide 5, th erefore m ore HBr in
dich lorom eth an e (2 × 0.1 m l) was added every 5 h . After th at, th e reaction m ixture was
worked up th ough it still con tain ed startin g com poun d. Th e solution was evaporated, th e
residue was dissolved in dich lorom eth an e (10 m l) an d extracted with water (3 × 10 m l). Th e
aqueous layer was con cen trated an d purified by silica gel ch rom atograph y (toluen e–EtOAc
2:1) to yield 17 m g (38%) of 16 as a colorless syrup; [α]D –54 (c 0.29, H2O). For C6H9BrO4
(224.0) calculated: 32.02% C, 4.03% H, 35.51% Br; foun d: 33.15% C, 4.33% H, 34.02% Br.
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1515
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