Molybdenum-catalyzed allylic substitution in glycals: A C-C bond-forming Ferrier-type reaction

Article abstract of DOI:10.1135/cccc20011735

The mild, Lewis-acidic complexes [Mo(CO)₄Br₂]₂, (MeCN)₂Mo(CO)₃(SnCl₃)Cl, and (acac)₂Mo(OTf)₂ have been found to catalyze the C(1)-specific C-glycosylation reaction of glycal acetates 1-3 with silyl enol ethers 4a-4c and electron-rich aromatics 5a, 5b (PhOMe, PhOH). While silyl enol ethers produce predominantly α-C-glycopyranosides (with 2 : 1 to 4 : 1 selectivity), aromatics tend to afford mainly β-C-glycopyranosides (2 : 1 to 3 : 1) in a thermodynamically controlled process.

Full text of DOI:10.1135/cccc20011735

Allylic Substitution in Glycals
1735
MOLYBDENUM-CATALYZED ALLYLIC SUBSTITUTION IN GLYCALS:
A C–C BOND-FORMING FERRIER-TYPE REACTION
b
c
Andrei V. MALKOVa1,b,+, Benjamin P. FARN , Nigel HUSSAIN
a2,b,+,
and Pavel KOČOVSKÝ
*
a
Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, U.K.;
1
2
e-mail: amalkov@chem.gla.ac.uk, p.kocovsky@chem.gla.ac.uk
Department of Chemistry, University of Leicester, Leicester LE1 7RH, U.K.
Glaxo SmithKline, Tonbridge, Kent TN11 9AN, U.K.
b
c
Received October 30, 2001
Accepted Novem ber 20, 2001
Dedicated to the memory of Dr Václav Černý, an unforgettable mentor of one of us (P. K.).
The mild, Lewis-acidic complexes [Mo(CO)4Br2]2, (MeCN)2Mo(CO)3(SnCl3)Cl, and (acac)2Mo(OTf)2
h ave been foun d to catalyze th e C(1)-specific C-glycosylation reaction of glycal acetates 1–3
with silyl en ol eth ers 4a–4c an d electron -rich arom atics 5a, 5b (Ph OMe, Ph OH). Wh ile silyl
enol ethers produce predominantly α-C-glycopyranosides (with 2 : 1 to 4 : 1 selectivity), arom atics
ten d to afford m ain ly β-C-glycopyran osides (2 : 1 to 3 : 1) in a th erm odyn am ically con trolled
process.
Keyw ord s: C-Glycosides; Carboh ydrates; Glycals; Allylic substitution s; Lewis acids; Stereo-
selective reaction s; Molybden um com plexes.
Glycals are versatile buildin g blocks in carboh ydrate ch em istry1; of particu-
lar im portan ce is th eir application as startin g m aterials in th e syn th esis of
C-glycosides an d oligosacch arides2,3. Bein g effectively allylic acetates (with
a corollary of furth er substituen ts), glycals are kn own to un dergo allylic
substitution in th e presen ce of eith er Lewis acids1,4–6 or palladium (0) com -
plexes7. As a rule, glycals afford C-1 substituted products on Lewis acid-
catalyzed reaction s1,2,4,5; form ation of th eir C-3 isom ers h as on ly been ob-
served in several in stan ces1,6. On th e oth er h an d, organ om etallics h ave
been sh own to be capable of judicious con trollin g th e C-1/C-3 selectivity.
Th us, for in stan ce, organ ozin c reagen ts ten d to afford C-1 alkylated prod-
+ Presen t address: Un iversity of Glasgow.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)
doi:10.1135/cccc20011735

1736
Malkov, Farn, Hussain, Kočovský:
ucts (in th e presen ce of BF3·OEt2 or Me3SiOTf)7, wh ereas Cu/Zn reagen ts
prefer th e reaction at C-3 un der sim ilar con dition s8. Heck addition an d
Pd(0)-catalyzed allylic substitution give C-1 products9,10, alth ough th e
regioselectivity of th e latter reaction can be altered, to som e exten t, by elec-
tron ic an d steric effects of th e substituen ts surroun din g th e in term ediate
π-allyl com plex10
.
We h ave recen tly reported on th e Mo(II)- an d Mo(IV)-catalyzed allylic
substitution with a variety of C-n ucleoph iles, such as silyl en ol eth ers of
sim ple keton es an d electron -rich arom atics an d h eteroarom atics11,12
(Sch em e 1). We h ave also dem on strated th at th e Mo(II) an d Mo(IV) com -
plexes A–C act as very m ild Lewis-acidic catalysts11,12, wh ich is in sh arp
con trast to Mo(0)- an d Pd(0)-com plexes, kn own to react via η3-coordin ated
in term ediates13,14. In view of th e ready availability of th e Mo(II)
(refs11e,11h ,15) an d Mo(IV) (refs12,16) catalysts an d th eir com patibility with
various n ucleoph iles, it was of in terest to exten d th is m eth odology to th e
carboh ydrate realm with a view of developin g a sim ple, n on -expen sive
route to various C-glycosides, based on th e Mo-catalyzed allylic substitution
in th e glycal m olecule.
OSiMe3
OR
O
R
R
OAc
[Mo]
[Mo]
OR
(acac)2MoIV(OTf)2
[MoII(CO)4Br2]2
(MeCN)2MoII(CO)3(SnCl3)Cl
Tf = CF3SO2
A
B
C
SCHEME 1
RESULTS AND DISCUSSION
D-Glucal triacetate (1) was selected as th e pilot m odel com poun d to explore
th e glycosylation reactivity an d to establish suitable reaction con dition s
(Ch art 1). With th e silyl en ol eth er derived from acetoph en on e (4a) an d
com plex A (2 m ole %) as catalyst in CH2Cl2 at room tem perature, a ≈2 : 1
m ixture of α- an d β-C-glycopyran osides17 6a an d 7a (Sch em e 2) was ob-
tain ed in good yield (Table I, en try 1) as th e result of a rem arkably fast reac-
tion (≤5 m in ). Sim ilarly fast reaction s were observed for th e rem ain in g two
catalysts B an d C, sh owin g little differen ce in th e reactivity, product ratios,
an d yields (en tries 2 an d 3). With th e silyl en ol eth ers 4b an d 4c (derived
from aceton e an d m eth yl isobutyrate, respectively), sligh tly h igh er α/β
an om eric ratios of th e products 6 an d 7 (≈3 : 1) were obtain ed (en tries 4–9).
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Allylic Substitution in Glycals
1737
O
O
O
AcO
AcO
AcO
AcO
AcO
AcO
AcO
AcO
AcO
1
2
3
OSiMe3
R2
R1
OR
R1
4a, R1 = H, R2 = Ph
4b, R1 = H, R2 = Me
4c, R1 = Me, R2 = OMe
5a, R = Me
5b, R = H
CHART 1
In th e D-galactal series 2 (with th e in verted con figuration at 4-position ),
sim ilar reactivities an d preferen ces h ave been observed (en tries 10–18), in -
dicatin g th at th e ch an ge of con figuration in th e vicin ity of th e allylic sys-
tem h as little in fluen ce on th e reaction course. In terestin gly, th e h igh est
α/β ratios were observed for 4c, th e m ost sterically h in dered n ucleoph ile
(up to 4 : 1; en tries 16–18). Th e con figuration al ch an ge with in th e allylic
system itself, as in D-allal triacetate 3, again did n ot affect th e reaction
significantly (entry 19), suggesting a common reaction intermediate in the case
of 1 an d 3. Th e Mo(IV) com plex C appears to be th e catalyst of ch oice as it
gave con sisten tly h igh er yields th an A or B in each series (en tries 3, 6, 9,
12, 15, an d 18).
Oxygen ated, electron -rich arom atics h ave tradition ally been regarded as
suitable substrates for glycosylation reaction s. In deed, our m olybden um
catalysts proved to catalyze th e glycosylation but th e products of th e reac-
tion of glycals 1–3 with an isole (5a, Sch em e 3) turn ed out be m ain ly th e
correspon din g β-an om ers 11a an d 13a, respectively (Table II, en tries 1–3
an d 7–12), wh ich con trasts with th e predom in an t α-glycosylation in th e
case of silyl en ol eth ers (vide supra). In terestin gly, ph en ol 5b produced th e
correspon din g C-glucoside, again predom in an tly as th e β-an om er 11b (Ta-
ble II, en tries 4–6), rath er th an th e expected O-glycoside, wh ich would be
typical for oth er Lewis-acidic catalysts1,18
.
Th e reactivity of th e arom atic don ors raised th e question s as to (i) th e ra-
tion ale for th e form ation of C-glycopyran osides 10b an d 11b in th e case of
ph en ol (rath er th an th e O-glycopyran osides) an d (ii) th e origin of th e pref-
eren ce for β-an om eric products 11 an d 13.
Sin ce Ph O of th e O-glycoside m ay, in prin ciple, serve as a leavin g group,
we en deavored to establish wh eth er th is was th e case with our Mo catalysts.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

1738
Malkov, Farn, Hussain, Kočovský:
R1
O
R1
O
R1
R1
O
R2
O
R2
[Mo]
1
3
+
+
4
4
AcO
AcO
AcO
+
CH2Cl2
rt, 10 min
AcO
6a, R1 = H, R2 = Ph
6b, R1 = H, R2 = Me
6c, R1 = Me, R2 = OMe
7a, R1 = H, R2 = Ph
7b, R1 = H, R2 = Me
7c, R1 = Me, R2 = OMe
O
R
O
R
[Mo]
AcO
AcO
AcO
2
+
4
+
O
O
CH2Cl2
rt, 10 min
AcO
8a, R = Ph
8b, R = Me
9a, R = Ph
9b, R = Me
SCHEME 2
TABLE I
C-Glycosylation of 4a–4d catalyzed by Mo com plexes A, B, or Ca
En try
Carboh ydrate Nucleoph ile
Catalyst
Products
α/β ratiob
Yield, %
1
2
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
4a
4a
4a
4b
4b
4b
4c
4c
4c
4a
4a
4a
4b
4b
4b
4c
4c
4c
4a
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
6a + 7a
6a + 7a
6a + 7a
6b + 7b
6b + 7b
6b + 7b
6c + 7c
6c + 7c
6c + 7c
8a + 9a
8a + 9a
8a + 9a
8b + 9b
8b + 9b
8b + 9b
8c + 9c
8c + 9c
8c + 9c
6a + 7a
63 : 37
60 : 40
65 : 35
72 : 28
71 : 29
70 : 30
73 : 27
74 : 26
75 : 25
72 : 28
73 : 27
76 : 24
71 : 29
72 : 28
71 : 29
80 : 20
78 : 22
79 : 21
64 : 36
61
60
64
79
83
88
63
65
68
60
63
66
79
77
85
70
69
72
75
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
a
b
Con dition s: catalyst (2 m ole %), CH2Cl2, rt, 10 m in (at 0.1 m m ol scale). Determ in ed by
th e 1H NMR spectrum of th e crude product m ixture.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Allylic Substitution in Glycals
1739
To th is en d, O-glycoside 14 was prepared from 1 via Ferrier reaction , ac-
cordin g to th e kn own procedure18 (Sch em e 4), an d subm itted to th e reac-
tion con dition s (2 m ole % of C at room tem perature). With in 5 m in , TLC
an alysis dem on strated a quan titative con version of 14 in to a 31 : 69 m ix-
OR
OR
[Mo]
1
3
+
+
PhOR
PhOR
O
O
AcO
AcO
AcO
AcO
+
CH2Cl2
rt, 10 min
5a, R = Me
5b, R = H
10a, R = Me
10b, R = H
11a, R = Me
11b, R = H
OMe
+
OMe
[Mo]
O
O
AcO
AcO
AcO
AcO
2
+
PhOMe
CH2Cl2
rt, 10 min
5a
12a
13a
SCHEME 3
TABLE II
C-Glycosylation of arom atics catalyzed by Mo com plexes A, B, or Ca
En try
Carboh ydrate Nucleoph ile
Catalyst
Product(s) α/β ratiob
Yield, %
1
2
1
1
1
1
1
1
2
2
2
3
3
3
Ph OMe
Ph OMe
Ph OMe
Ph OH
A
B
C
A
B
C
A
B
C
A
B
A
10a + 11a
10a + 11a
10a + 11a
10b + 11b
10b + 11b
10b + 11b
12a + 13a
12a + 13a
12a + 13a
10a + 11a
10a + 11a
10a + 11a
25 : 75
27 : 73
28 : 72
35 : 65
33 : 67
34 : 66
35 : 65
33 : 67
32 : 68
24 : 76
27 : 73
26 : 74
40
42
45
45
47
45
39
43
46
51
48
54
3
4
5
Ph OH
6
Ph OH
7
Ph OMe
Ph OMe
Ph OMe
Ph OMe
Ph OMe
Ph OMe
8
9
10
11
12
a
b
Con dition s: catalyst (2 m ole %), CH2Cl2, rt, 10 m in (at 0.1 m m ol scale). Determ in ed by
th e 1H NMR spectrum of th e crude product m ixture.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

1740
Malkov, Farn, Hussain, Kočovský:
ture of α- an d β-C-glycopyran osides 10b/11b (86%), wh ich is practically
iden tical with th e results of th e glycosylation reaction of ph en ol 5b with 1
(Table II, en try 6). Sim ilarly, catalyst A afforded a ≈1 : 1 m ixture (76%) an d
B furn ish ed a ≈1 : 2 m ixture (95%) of 10b an d 11b. Th is beh avior h as n ot
been reported for oth er Lewis-acidic catalysts, wh ich dem on strates th e un -
usual properties of th e Mo(II) an d Mo(IV) catalysts.
O
O
PhOH, I2
[Mo]
AcO
AcO
10b + 11b
1
CH2Cl2
rt, 4 h
CH2Cl2
rt, 5 min
14
SCHEME 4
Th e differen ces in th e stereoch em ical outcom e of th e glycosylation of 4
versus 5 can be un derstood as follows: th e preferred attack by th e
n ucleoph ile at th e allylic cation 15, gen erated by th e rem oval of AcO–
(Sch em e 5), sh ould be pseudoaxial, owin g to th e stereoelectron ic effects.
Hen ce, glycosylation sh ould prim arily produce th e α-an om er, as in th e case
of th e silyl en ol eth ers 4a–4c. However, un like O-glycosides, th e α-an om ers
[Mo]+
− AcO−
1
5
O
O
+
1
[Mo]
AcO
AcO
AcO
AcO
− PhO−
14
Nu
15
10a
:
4
OMe
α-glycoside
[
]
Mo
O
O+Me
[
]
Mo
O
H
AcO
AcO
AcO
AcO
H
16
16'
O+Me
11a
AcO
H
HO
H
6
6
H
AcO
AcO
1
+
+
OMe
OMe
1
AcO
HO
H
17'
17
10a
SCHEME 5
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Allylic Substitution in Glycals
1741
of C-glycosides are n ot stabilized by th e stereoelectron ic effect (owin g to
th e h igh er level of th e LUMOC(1)–C as com pared with th e LUMOC(1)–O), leav-
in g space for th e α → β equilibration . In fact, with th e arom atic C-glycosides,
th e en docyclic oxygen can , in prin ciple, serve as a leavin g group, gen erat-
in g ben zylic cation 16 th at can un dergo a C–C bon d rotation to 16′, wh ose
cyclization would produce β-an om er 11a. However, cation 16/16′ is likely
to be furth er stabilized by con jugation with th e allylic double bon d, wh ich
would dictate th at th e arom atic rin g an d th e four carbon s C(1) to C(4) be in
th e sam e plan e, as in 17 an d 17′. Cyclization of th e delocalized cation 17
will produce β-an om er 11a, wh ereas its con form ation al isom er 17′ would
cyclize to give α-an om er 10a. Th e latter rin g closure, h owever, would pro-
ceed via a h igh er-en ergy tran sition state owin g to th e clash of C-6 with 1-H,
thereby favoring the 17 → 11a pathway. Treatm ent of the pure α-C-glucoside
10a with catalyst C resulted in th e form ation of a 1 : 2 m ixture of 10a an d
11a, wh ich supports th is equilibration m ech an ism .
In con clusion , we h ave developed a protocol for m ild, C(1)-specific
glycosylation of silyl en ol eth ers an d arom atics with glycals (e.g., 1 + 4 → 6
an d 1 + 5 → 11), catalyzed by Lewis-acidic com plexes [Mo(CO)4Br2]2,
(MeCN)2Mo(CO)3(Sn Cl3)Cl, an d (acac)2Mo(OTf)2. Wh ile silyl en ol eth ers
produced predom in an tly α-C-glycopyran osides (with 2 : 1 to 4 : 1 selec-
tivity), aromatics afforded mainly β-C-glycopyranosides (2 : 1 to 3 : 1) in a thermo-
dynamically controlled isomerization process.
EXPERIMENTAL
Gen eral Meth ods
Th e NMR spectra were recorded in CDCl3, 1H at 250 MHz an d 13C at 62.9 MHz with ch loro-
form -d1 (δ 7.26, 1H; δ 77.0, 13C) as in tern al stan dard; ch em ical sh ifts are given in ppm
(δ-scale), couplin g con stan ts (J) in Hz; 2D-tech n iques were used to establish th e structures
an d to assign th e sign als. Th e IR spectra were recorded for a th in film between KBr plates
un less oth erwise stated. Th e m ass spectra (EI an d/or CI) were m easured on a dual sector
m ass spectrom eter usin g direct in let an d th e lowest tem perature en ablin g evaporation . All
reaction s were perform ed un der an atm osph ere of dry, oxygen -free n itrogen in oven -dried
glassware. Solven ts an d solution s were tran sferred by syrin ge-septum an d can n ula tech -
n iques. Th e iden tity of th e products prepared by differen t m eth ods was ch ecked by com pari-
son of th eir NMR, IR, an d MS data an d by th e TLC beh avior. Most of th e products are
kn own com poun ds: 6a19, 6b19c,20, 6c5c, 7a19, 7b20c, 7c5c, 8a19b, 8b20c, 8c5c, 9a19b, 9b20c
,
9c5c, 10a21, 11a21, 12a21a, 13a21a, an d 1418. Th e startin g glycal triacetates 1–3 were prepared
from th e correspon din g glycals, of wh ich D-glucal an d D-galactal are com m ercially available,
wh ile D-allal was syn th esized accordin g to th e literature procedure4b,22. Th e silyl en ol eth ers
were obtain ed in th e sam e m an n er as reported in our previous paper11h
.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

1742
Malkov, Farn, Hussain, Kočovský:
Dibrom om olybden um Tetracarbon yl Dim er (A)
A solution of brom in e (1.36 g, 8.5 m m ol) in dich lorom eth an e (10 m l) was added to a sus-
pen sion of th e fin ely groun d m olybden um h exacarbon yl (2.24 g, 8.5 m m ol) in deoxy-
gen ated dich lorom eth an e (60 m l) at –78 °C; th e m ixture gradually evolved carbon m on oxide
an d th e solid dissolved. Th e solution was m ain tain ed at –78 °C for 1 h an d th e solven t was
th en evaporated un der reduced pressure at –78 °C to yield com plex A as an oran ge, crystal-
lin e solid (3.03 g, 97%). Pure product, wh ich could be stored in a freezer un der n itrogen for
several m o n t h s, w as o b t ain ed b y recryst allizat io n fro m M eC N . IR (C H 2 C l2 ): ν(C≡O)
2 100 (s), 2 020 (m ), 1 980 (m ), 1 960 (m ) cm –1 in accordan ce with th e literature15d,15e
.
Bis(aceton itrile)tricarbon ylch loro(trich lorostan n yl)m olybden um (B)
A n itrogen -purged m ixture of m olybden um h exacarbon yl (4.0 g, 15.4 m m ol) an d dry de-
gassed aceton itrile (120 m l) was h eated un der reflux for 24 h to give a yellow/ligh t brown
solution. The solution was cooled to room tem perature and tin(IV) chloride (3.18 g, 15.4 m m ol)
was added, th e m ixture was stirred for 10 m in , an d th e solven t was rem oved in vacuum to
give a dark red solid. Th e latter solid was redissolved in dry aceton itrile (30 m l) an d filtered
th rough a sin tered glass filter, wh ich rem oved a black tar residue an d gave an oran ge/red
filtrate. Removal of the solvent furnished complex B as a red/orange solid (6.39 g, 79%). IR (CH2Cl2):
ν(C≡O) 2 027 (s), 1 990 (s), 1 953 (m), 1 915 (w); ν(C≡N) 2 320 (w), 2 285 (w) cm –1. IR (Nujol):
ν(C≡O) 2 030 (m ), 1 955 (m ), 1 920 (br); ν(C≡N) 2 310 (w), 2 295 (w) cm –1 in accordan ce
with th e literature11,15
.
Bis(pen tan e-2,4-dion ato)m olybden um (IV) Ditriflate (C)
Th is com plex was gen erated in situ by addin g silver triflate (10 m g, 0.039 m m ol) to a solu-
tion of (acac)2MoCl2 (5 m g, 0.014 m m ol)12,16 in dry CH2Cl2 (10 m l) prior to each reaction .
Gen eral Procedure for th e Glycosylation Reaction s Catalyzed by Com plexes A–C
Catalyst A, B, or C (2 m ole %) was added to a solution of glycal (150 m g, 0.55 m m ol) an d
th e n ucleoph ile (0.65 m m ol) in dich lorom eth an e an d th e resultan t m ixture was stirred at
room tem perature for 5 m in upon wh ich tim e all startin g m aterials h ad been con sum ed, as
eviden ced by TLC. Th e m ixture was successively wash ed with water (2 × 50 m l) an d satu-
rated sodium h ydrogen carbon ate (2 × 50 m l). Th e organ ic layer was th en separated an d
dried an d th e solven t was evaporated. Th e crude product was purified by flash ch rom atogra-
ph y on silica gel (5 g) with a petroleum eth er–eth er m ixture (1 : 1) as eluen t, to give a m ix-
ture of an om eric glycosides; for th e ratios (determ in ed by 1H NMR with referen ce to th e
ratios of 6-H an d selected oth er proton s) an d yields (isolated yields of th e an om eric m ix-
tures), see Table I. Th e m ixture was th en separated in to α- an d β-glycopyran osides by ch ro-
m atograph y on silica gel (10 g) with a petroleum eth er–eth er m ixture (90 : 10) for th e
purpose of ch aracterization .
Rearran gem en t of O- to C-Glycoside
Catalyst A, B, or C (2 m ole %) was added to a solution of O-glycopyran oside 14 (70 m g,
0.22 m m ol) in dich lorom eth an e (5 m l) an d th e m ixture was stirred at room tem perature for
5 m in , wh ereupon com pletion of th e reaction was observed by TLC. Th e resultan t products
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Allylic Substitution in Glycals
1743
were purified by flash ch rom atograph y on silica gel (5 g) with a petroleum eth er–eth er m ix-
ture (1 : 1) as eluen t to yield th e rearran ged C-glycopyran osides 10b an d 11b; th e resultin g
α/β ratios an d yields are discussed in th e text.
4-(4,6-Di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)phenol (10b). 1H NMR: 2.06 s,
3 H (AcO); 2.09 s, 3 H (AcO); 3.72 ddd, J = 5.9, 5.7, 3.1, 1 H (5′-H); 4.07 dd, J = 12.0, 3.1, 1 H
(6′-Ha); 4.25 dd, J = 12.0, 5.7, 1 H (6′-Hb); 5.27 m , W/2 = 6.0, 1 H (1′-H); 5.28–5.38 m , 1 H
(4′-H); 5.95 m , 1 H (3′-H); 6.15 m , 1 H (2′-H); 6.84 br d, J = 8.5, 2 H (arom .); 7.29 br d, J =
8.5, 2 H (arom .). 13C NMR: 20.8 (q), 21.1 (q), 63.0 (t), 65.2 (d), 68.9 (d), 73.5 (d), 115.3 (d),
125.0 (d), 129.7 (d), 130.7 (s), 131.7 (d), 156.0 (s), 170.6 (s), 171.0 (s). EI HRMS: 307.11816
(C16H19O6 requires MH+, 307.11817).
4-(4,6-Di-O-acetyl-2,3-dideoxy-β-D-erythro-hex-2-enopyranosyl)phenol (11b). 1H NMR: 2.00 s,
3 H (AcO); 2.04 s, 3 H (AcO); 3.95 ddd, J = 8.5, 5.7, 2.8, 1 H (5′-H); 4.12 dd, J = 12.2, 5.7, 1 H
(6′-Ha); 4.21 dd, J = 12.2, 2.8, 1 H (6′-Hb); 5.08 m , W/2 = 6.5, 1 H (1′-H); 5.34 dp, J = 8.4,
1.5, 1 H (4′-H); 5.76 dt, J = 10.4, 1.8, 1 H (3′-H); 5.84 dt, J = 10.4, 1.3, 1 H (2′-H); 6.73 br d, J =
8.6, 2 H (arom .); 7.13 br d, J = 8.6, 2 H (arom .). 13C NMR: 21.3 (q), 21.5 (q), 64.2 (t), 66.0
(d), 75.2 (d), 77.6 (d), 115.9 (d), 125.2 (d), 129.3 (d), 132.1 (s), 133.3 (d), 156.5 (s), 171.0 (s),
171.6 (s). IR: ν(OH) 3 590; ν(arom . C–H) 2 960, 2 930, 2 860; ν(C=O) 1 745, 1 740 cm –1. EI
MS (m/z, %): 307 (MH+). EI HRMS: 307.11817 (C16H19O6 requires MH+, 307.11817).
We thank the EPSRC and Glaxo SmithKline for a CASE award to B. P. F.
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=
8.7). In the 13C NMR spectra, C-5 in the α-anomer is always more shielded, as reflected
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C-glycosides 6–13 are known compounds (see the Experimental), the structural
identification of our products was based mainly on the comparison of their NMR spectra
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Allylic Substitution in Glycals
1745
with the published data. In addition, NOE experiments (especially the occurrence vs
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