Synthesis of C-aryl furanosides by the 'reverse polarity' strategy

Full text of DOI:10.1021/jo951344o

J . Org. Chem. 1996, 61, 2191-2194
2191
Notes
Sch em e 1
Syn th esis of C-Ar yl F u r a n osid es by th e
“Rever se P ola r ity” Str a tegy
Kathlyn A. Parker*,1 and Dai-Shi Su2
Department of Chemistry, Brown University,
Providence, Rhode Island 02912
Received J uly 24, 1995
The C-aryl glycoside antitumor antibiotics have served
as the inspiration for the recent development of synthetic
methods which connect the polyketide “aglycone” and the
carbohydrate appendage.3 One of these methods, devel-
oped in our labs, is based on a novel application of the
umpolung concept. It uses the addition of a lithio glycal
to a quinol ketal or quinone and the reductive or
nonreductive aromatization of the adduct as the key
steps.4
To date, these methods have been applied only in the
context of the preparation of C-aryl pyranosides. We are
now pleased to report the extension of this strategy to
the synthesis of C-aryl furanosides with the efficient
preparation of model compounds 1 and 2.
On the other hand, both reductive aromatization and
anti-Markovnikov hydration could be effected in one
procedure by treatment of crude 5 with 5 mol equiv of
borane-THF followed by stirring with basic hydrogen
peroxide. The resulting C-aryl glycoside was isolated and
characterized as the 2′-acetate 1a , obtained in an overall
40% yield from glycal 3. The stereochemistry of this
product was determined by an NOE difference experi-
ment. The NOE enhancements are shown on the struc-
ture in Scheme 1.
The four-step procedure described above was conve-
nient and gave an acceptable overall yield. However, we
imagined that we might have use for derivatives in which
the phenolic hydroxyl group was free or protected by an
easily removable group. We needed then to be able to
effect the reductive aromatization of quinol glycal 7a .
Substrate 7a was most conveniently obtained (Scheme
2) by the addition of the lithio reagent derived from glycal
3 to benzoquinone (6a ).
Ela bor a tion of a Tr a n s-Disu bstitu ted F u r a n oid
Glyca l. Syn th esis of C-1 Ar yl Ar a bin ofu r a n osid es 1.
The known trans-disubstituted furanoid glycal 3 was
prepared from D-ribose according to Ireland’s method.5
Lithiation of this compound and addition of the resulting
reagent to quinone ketal 4 gave quinol ketal 5, contami-
nated with significant amounts of the starting material
4. The components of this mixture could not be sepa-
rated. Therefore the crude product was used in subse-
quent reactions, and byproducts were removed at a later
stage. The attempted reduction of crude adduct 5 with
sodium dithionite afforded none of the C-aryl glycal.
Instead quinol 7a , the hydrolysis product, was obtained
in 53% yield.
Attempts to apply literature methods for reductive
aromatization of quinols to the glycal-substituted quinol
6 4b
7a resulted in recovery of starting material (with NaBH4 )
or hydrolytic ring opening and dehydration (with
Na2S2O4,4b Al/Hg,7 Li/NH3 to afford ketone 8 and furan
9). Similarly, treatment with Li(Ot-Bu)3AlH or Red-Al
resulted in the recovery of starting material 7a , and
treatment with LiAlH4 or DIBAL-H gave the dehydration
product 9.
On the other hand, under controlled conditions (0 °C
to room temperature), treatment with BH3‚THF (5 equiv)
followed by stirring with basic hydrogen peroxide con-
verted quinol 7a to the desired aryl glycoside. The
BH3‚THF reagent gave better yields than the BH3‚SMe2
(1) Recipient of an NSF Career Advancement Award, 1992-1993.
(2) Government Assistance in Areas of National Needs Fellow,
1993-95.
(3) For excellent reviews, see: (a) Postema, M. H. D. Tetrahedron
1992, 48, 8545. (b) Suzuki, K.; Matsumoto, T. In Recent Progress in
the Chemical Synthesis of Antibiotics and Related Microbial Products;
Lukacs, G., Ed.; Springer Verlag: Berlin, 1993; Vol. 2, pp 352-403.
(c) J aramillo, C.; Knapp, S. Synthesis 1994, 1. (d) Postema, M. H. D.
In C-Glycoside Synthesis; Rees, C. W., Ed.; CRC Press: Boca Raton,
FL, 1995.
(4) (a) Parker, K. A.; Coburn, C. A. J . Am. Chem. Soc. 1991, 113,
8516. (b) Parker, K. A.; Coburn, C. A. J . Org. Chem. 1992, 57, 5547.
(c) Parker, K. A.; Koh, Y.-h. J . Am. Chem. Soc. 1994, 116, 11149-
11150. (d) Parker, K. A.; Coburn, C. A.; Koh, Y.-h. J . Org. Chem. 1995,
60, 2938.
(5) (a) Ireland, R. E.; Thaisrivongs, S.; Vanier, N.; Wilcox, C. S. J .
Org. Chem. 1980, 45, 48. (b) Ireland, R. E.; Norbeck, D. W.; Mandel,
G. S.; Mandel, N. S. J . Am. Chem. Soc. 1985, 107, 3285.
(6) Manning, M. J .; Henton, D. R.; Swenton, J . S. Tetrahedron Lett.
1977, 1679.
(7) Stahly, G. P.; Bell, D. R. J . Org. Chem. 1989, 54, 2873.
0022-3263/96/1961-2191$12.00/0 © 1996 American Chemical Society

2192 J . Org. Chem., Vol. 61, No. 6, 1996
Notes
Sch em e 2
Sch em e 3
Sch em e 4
(BMS) reagent. Without purification, the crude product
was protected as the corresponding diacetate 1b, which
was obtained in an overall yield of 68%. A similar
sequence converted quinol 7b to C-aryl furanoside 1c in
71% yield.
Ela bor a tion of a Cis-Disu bstitu ted F u r a n oid Gly-
ca l. Syn th esis of C-1 Ar yl Glu cofu r a n osid es 2. In
order to determine the generality of the chemistry
described above, the reductive aromatization schemes
were examined in a furanoglycal system in which the 3-
and 5-substituents were cis (Scheme 3). We chose to
work with substrates derived from the known furanoid
glycal 10 (prepared by the literature procedure from
D-mannose).8
Lithiation of glycal 10 gave a reagent which added to
quinol ketal 4, affording adduct 11. The attempted
reduction of 11 with sodium dithionite gave the hydroly-
sis product, quinol 12a , in 90% yield.
Reductive aromatization proceeded, however, when the
borane protocol (-15 °C, 4 h) was applied to quinol acetal
11. As expected, borane added to the glycal double bond
on the side opposite the substituents. After acylation, a
70% overall yield of C-glycoside 2a was obtained. The
stereochemistry of this reductive aromatization/hydrobo-
ration product was verified by an NOE difference experi-
ment. The enhancement is shown on the structure in
Scheme 3.
6a and 6b respectively (Scheme 4). Treatment of quinol
12a with BH3‚THF (-15 °C, 4 h) followed by stirring with
NaOH/H2O2 and acylation gave C-aryl furanoside 2b in
an overall yield of 54%. Likewise, quinol 12b was
converted to C-aryl furanoside 2c in 43% overall yield.
The cis-disubstituted dihydrofurans 12a and 12b were
reduced by BH3‚THF at lower temperature and in shorter
reaction times than the trans-disubstituted substrates
7a and 7b.
Con clu sion s
The reverse polarity strategy provides an alternative
to conventional C-glycosylation methods for the prepara-
tion of C-aryl furanosides with some stereochemical
patterns. These procedures are simple and good yields
are obtained. We are continuing to examine applications
of this methodology in the context of natural product
synthesis.
Reductive aromatization of quinol substrates was also
examined with the quinol substrates 12a and 12b,
prepared by addition of lithiated glycal 10 to quinones
Exp er im en ta l Section
Solvents were dried and purified by standard methods before
use. Ether refers to diethyl ether. Flash chromatography was
performed with silical gel (0.035-0.07 mm). Bromobenzo-
(8) Ghosh, A. K.; McKee, S. P.; Thompson, W. J . J . Org. Chem. 1991,
56, 6500.

Notes
J . Org. Chem., Vol. 61, No. 6, 1996 2193
quinone (6b) was prepared according to the procedure of Carlson
1H), 4.87 (d, J ) 4.1 Hz, 1H), 4.41 (t, J ) 3.5 Hz, 1H), 4.09 (m,
1H), 3.77 (m, 5H), 2.05 (s, 3H), 0.93 (“s”, 18H), 0.12 (“s”, 12H);
13C NMR (CDCl3) δ 170.2, 159.6, 132.7, 128.0, 114.3, 113.9, 86.6,
85.8, 84.6, 77.3, 63.0, 55.6, 26.1, 26.0, 25.7, 21.2, -4.8, -5.3;
FTIR (neat) 1747, 1233 cm-1; HRMS (FAB) calcd 451.2670,
found 451.2678 (M - OAc).
and Miller and used without purification.9
Qu in ol Glyca l 7a fr om 3 a n d 6a . To a solution of 202 mg
(0.586 mmol) of glycal 35 in 4 mL of THF at -78 °C was added
1.1 mL (1.87 mmol) of t-BuLi (1.7 M in pentane). The solution
was stirred at -78 °C for 1 h and then added dropwise by
cannula to a solution of 86 mg (0.796 mmol) of p-benzoquinone
6a in 20 mL of THF at -78 °C . The dark reaction mixture was
stirred for 4 h, quenched with 25 mL of H2O, and extracted with
CH2Cl2 (3 × 40 mL). The combined organic solution was dried
with Na2SO4, filtered, and concentrated. Chromatography (3:1
hexanes/EtOAc) gave 229 mg (86%) of a yellow oil: 1H NMR
(CDCl3) δ 6.90 (ddd, J ) 10.4, 3.2, 2.1 Hz, 2H), 6.19 (ddd, J )
10.2, 3.4, 1.9 Hz, 2H), 5.01 (d, J ) 2.6 Hz, 1H), 4.93 (t, J ) 2.9
Hz, 1H), 4.36 (dd, J ) 5.3, 2.2 Hz, 1H), 3.69 (dd, J ) 9.9, 5.1 Hz,
1H), 3.57 (dd, J ) 9.8, 5.5 Hz, 1H), 0.88 (“s”, 18H), 0.06 (“s”,
12H); 13C NMR (CDCl3) δ 185.0, 158.5, 147.0, 128.8, 128.6, 100.6,
90.2, 66.9, 62.6, 25.8, 18.1, -4.28, -4.44, -5.40, -5.45; IR (neat)
3381, 1673, 1651 cm-1; HRMS (FAB, NaI) calcd 475.2312, found
475.2318 (M + Na).
Qu in ol Glyca l 7a fr om Qu in ol Keta l 5. To a solution of
31 mg (ca. 0.062 mmol) of crude quinol ketal 5 in 1 mL of THF/
H2O (3:1) was added 54 mg (0.31 mmol) of sodium dithionite.
The solution was stirred at rt for 8.5 h. The reaction mixture
was quenched with H2O (20 mL) and extracted with CH2Cl2 (3
× 30 mL), and the combined organic layers were dried with Na2-
SO4, filtered, and concentrated. Preparative TLC (3:1 hexanes/
EtOAc with 1% Et3N) afforded 18 mg (53% from glycal 3) of a
yellow oil.
Br om oqu in ol Glyca l 7b. To a solution of 90 mg (0.261
mmol) of glycal 35 in 2 mL of THF at -78 °C was added 0.5 mL
(0.85 mmol) of t-BuLi (1.7 M in pentane). The solution was
stirred at this temperature for 1 h and then added dropwise by
cannula to a solution of 44 mg (0.235 mmol) of bromobenzo-
quinone (6b)9 in 10 mL of THF at -78 °C. The dark reaction
mixture was stirred for 9 h and then quenched with 20 mL of
H2O and extracted with CH2Cl2 (3 × 25 mL). The combined
organic solution was dried with Na2SO4, filtered, and concen-
trated. Chromatography (3:1 hexanes/EtOAc) gave 121 mg
(87%) of a yellow oil: 1H NMR (CD2Cl2) δ 7.34 (dd, J ) 2.8, 1.0
Hz, 1H), 6.9 (dd, J ) 10.0, 3.0 Hz, 1H), 6.3 (dd, J ) 10.0, 1.0 Hz,
1H), 5.09 (t, J ) 2.3 Hz, 1H), 4.94 (t, J ) 2.3 Hz, 1H), 4.33 (m,
1H), 3.79 (dd J ) 11.0, 4.9 Hz, 1H), 3.61 (dd, J ) 11.1, 5.1 Hz,
1H), 2.97 (s, 1H), 0.88 (s, 18H), 0.05 (s, 12H); 13C NMR (CD2Cl2)
δ 178.0, 158.0, 147.7, 147.6, 133.2, 127.7, 101.6, 90.9, 76.6, 69.8,
63.1, 25.9, 18.5, -4.4, -5.3; FTIR (neat) 3406, 1673, 1605, 1257
cm-1; HRMS (FAB, NaI) calcd 555.1397, found 555.1390 (M +
Na, 81Br).
Mon oa ceta te 1a . To a solution of 168 mg (0.49 mmol) of
glycal 34 in 5 mL of THF at -78 °C was added 0.9 mL (1.53
mmol) of t-BuLi (1.7 M in pentane). The resulting solution was
stirred at -78 °C for 30 min and then added dropwise by cannula
to a solution of 65 mL (0.47 mmol) of 4,4-dimethoxy-2,5-
cyclohexadien-1-one (4) in 5 mL of THF at -78 °C. The yellow
reaction mixture was stirred at -78 °C for 5 h and 45 min,
quenched with 50 mL of H2O, and extracted with EtOAc (4 ×
30 mL). The combined EtOAc solution was washed with brine
(2 × 100 mL), dried with Na2SO4, filtered, and concentrated to
give 241 mg of crude product 5. To a solution of 39 mg of this
material in 1 mL of THF at 0 °C was added 0.4 mL (0.4 mmol)
of BH3‚THF (1 M solution in THF) dropwise over 5 min. The
resulting solution was stirred at 0 °C for 3 h and quenched with
1 mL of MeOH and 2 mL of 3 N NaOH/H2O2 (1/1) solution. The
resulting mixture was stirred at rt for 3.5 h and then partitioned
between brine (15 mL) and EtOAc (4 × 20 mL). The combined
organic solution was washed with brine (2 × 20 mL), dried with
Na2SO4, and concentrated. To a solution of the crude product
in 1 mL of pyridine were added a catalytic amount of DMAP
and 0.5 mL of Ac2O. The reaction mixture was stirred at rt
overnight, quenched with 20 mL of H2O, and extracted with CH2-
Cl2 (4 × 20 mL). The combined organic solution was dried over
Na2SO4, filtered, and concentrated. Chromatography (one col-
umn with CH2Cl2 and then one with 3:1 hexanes/EtOAc) gave
10 mg (40% overall) of a yellow oil: 1H NMR (CDCl3) δ 7.34 (d,
J ) 8.5 Hz, 2H), 6.85 (d, J ) 8.6 Hz, 2H), 5.11 (t, J ) 4.0 Hz,
Dia ceta te 1b. To a solution of 54 mg (0.13 mmol) of quinol
glycal 7a in 1 mL of THF at 0 °C was added 0.65 mL (0.65 mmol)
of BH3‚THF (1 M solution in THF). The reaction mixture was
gradually warmed up to rt overnight and then quenched with 2
mL of MeOH and 3 mL of 3 N NaOH/H2O2 (1/1) solution. The
resulting mixture was stirred at rt for 8.5 h and then extracted
with ether (3 × 20 mL). The combined organic solution was
washed with H2O (1 × 30 mL), dried with Na2SO4, and
concentrated. To a solution of the crude product in 1 mL of
pyridine were added a catalytic amount of DMAP and 0.6 mL
of Ac2O. The resulting solution was stirred at rt for 11 h,
quenched with 5 mL of H2O, and extracted with CH2Cl2 (3 × 20
mL). The combined organic solution was dried with Na2SO4,
filtered, concentrated, and subjected to chromatography (9:1
hexanes/EtOAc) to give 48 mg (68% overall) of a yellow oil: 1H
NMR (CDCl3) δ 7.44 (d, J ) 8.2 Hz, 2H), 7.04 (d, J ) 8.7 Hz, 2
H), 5.1 (t, J ) 2.8 Hz, 1H), 4.97 (d, J ) 3.3 Hz, 1H), 4.41 (t, J )
3.0 Hz, 1 H), 4.15 (m, 1H), 3.77 (m, 1H), 2.27 (s, 3H), 2.1 (s,
3H), 0.9 (“s”, 18H), 0.1 (“s”, 12H); 13C NMR (CD2Cl2) δ 170.2,
169.7, 138.4, 127.7, 127.6 87.2, 86.0, 84.7, 77.4, 63.0, 26.1, 25.9,
25.6, 21.2, 18.6, -4.9, -5.3; FTIR (neat) 1745, 1370, 1196 cm-1
HRMS (FAB), calcd 539.2860, found 539.2868 (M + H).
;
Dia ceta te 1c. To a solution of 34 mg (0.071 mmol) of quinol
glycal 7b in 1 mL of THF at 0 °C was added 0.4 mL (0.4 mmol)
of BH3‚THF (1 M solution in THF). The reaction mixture was
gradually warmed up to rt overnight and then quenched with 2
mL of MeOH and 3 mL of 3 N NaOH/H2O2 (1/1). The resulting
mixture was stirred at rt for 8.5 h and extracted with ether (3
× 20 mL) The combined ether solution was washed with H2O (1
× 30 mL), dried with Na2SO4, and concentrated. The crude
product was dissolved in 1 mL of pyridine and to this solution
was added a catalytic amount of DMAP and 0.6 mL of Ac2O.
The resulting solution was stirred at rt for 11 h, quenched with
5 mL of H2O, and extracted with CH2Cl2 (3 × 20 mL). The
combined organic solution was dried with Na2SO4, filtered, and
concentrated. Chromatography (9:1 hexanes/EtOAc) gave 31 mg
(71% overall) of a yellow oil: 1H NMR (CD2Cl2) δ 7.73 (s, 1H),
7.42 (d, J ) 8.5 Hz, 1H), 7.08 (d, J ) 8.4 Hz, 1H), 5.05 (t, J )
2.5 Hz, 1H), 4.98 (d, J ) 2.6 Hz, 1H), 4.40 (t, J ) 2.4 Hz, 1H),
4.2 (m, 1H), 3.75 (m, 2H), 2.32 (s, 3H), 2.1 (s, 3H), 0.9 (“s”, 18H),
0.1 (“s”, 12H); 13C NMR (CD2Cl2) δ 170.3, 168.8, 140.7, 131.3,
126.7, 124.2, 123.7, 87.9, 86.0, 84.5, 77.5, 63.0, 29.1, 26.1, 25.6,
21.2, 21.0, -4.9, -5.2; FTIR (neat) 1771, 1748, 1232 cm-1; HRMS
(FAB) calcd 617.1965, found 617.1959 (M + H, 79Br).
Qu in ol Keta l Glyca l 11. The procedure used for the
preparation of quinol ketal glycal 5 was applied to lithiation of
149 mg (0.49 mmol) of glycal 108 with 1 mL of t-BuLi (1.7M
solution in pentane) and addition to quinone ketal 4 (68 mL,
0.49 mmol) to give 120 mg (78%) of a yellow oil: 1H NMR (CDCl3)
δ 6.17 (d, J ) 10.2 Hz, 2H), 5.94 (d, J ) 10.5 Hz, 2H), 4.93 (m,
2H), 4.45 (m, 2H), 4.08 (m, J ) 9.5, 6.4 Hz, 1H), 3.90 (dd, J )
9.5, 5.9 Hz, 1H), 3.28 (s, 1H), 3.20 (s, 1H), 2.44 (s, 1H), 1.41 (s,
3H), 1.33 (s, 3H), 0.86 (s, 9H), 0.03 (s, 3H), 0.01 (s, 3H); 13C NMR
(CDCl3) δ 161.6, 133.7, 133.6, 128.2, 128.0, 108.6, 100.2, 93.5,
85.6, 73.9, 73.4, 65.9, 65.7, 50.4, 50.2, 26.5, 25.7, 25.1, -4.6, -5.0;
FTIR (neat) 3382, 1672, 1066 cm-1; HRMS (FAB, NaI); calcd
477.2284, found 477.2288 (M + Na).
Qu in ol Glyca l 12a fr om 10 a n d 6a . A 50-mg sample (0.167
mmol) of glycal 108 was lithiated (t-BuLi, 1.7 M solution in
pentane, 0.5 mL) and coupled with 6a (24 mg, 0.222 mmol) in a
procedure resembling that for preparing 7a to give 52 mg (76%)
of a yellow oil: 1H NMR (CDCl3) δ 6.88 (dd, J ) 10.1, 1.7 Hz,
2H), 6.22 (dd, J ) 10.0, 2.3Hz, 2H), 5.04 (d, J ) 3.6 Hz, 1H),
4.96 (dd, J ) 2.5, 7.0 Hz, 1H), 4.46 (m, 2H), 4.04 (dd, J ) 9.8,
6.6 Hz, 1H), 3.88 (dd, J ) 9.7, 6.7 Hz, 1H), 3.07 (s, 1H), 1.39 (s,
1H), 1.32 (s, 3H), 0.84 (s, 9H), 0.03 (s, 3H), 0.02 (s, 3H); 13C NMR
(CD2Cl2) δ 185.1, 159.8, 147.2, 129.1, 109.0, 101.8, 86.3, 74.2.
73.8, 67.3, 65.9, 26.6, 25.9, 25.3, 18.4, -4.5, -4.9; FTIR (neat)
3348 1673, 1066 cm-1; HRMS (EI) calcd 333.1522, found
333.1526 (M - C3H7O2).
Qu in ol Glyca l 12a fr om Qu in ol Keta l 11. To a solution of
112 mg (0.247 mmol) of quinol ketal 11 in 2 mL of THF/H2O
(9) Carlson, B. W.; Miller, L. L. J . Am. Chem. Soc. 1985, 107, 479.

2194 J . Org. Chem., Vol. 61, No. 6, 1996
Notes
(3:1) was added 165 mg (0.948 mmol) of sodium dithionite. The
solution was stirred at rt for 4.5 h. The reaction mixture was
quenched with H2O (10 mL) and extracted with CH2Cl2 (3 × 20
mL), and the combined organic layers were dried with Na2SO4,
filtered, and concentrated. Preparative TLC (3:1 hexanes/
EtOAc) afforded 91 mg (90%) of a yellow oil.
Br om oqu in ol Glyca l 12b. The procedure used for the
preparation of bromoquinol glycal 7b was applied with 41 mg
(0.14 mmol) of glycal 10,8 0.4 mL t-BuLi (1.7 M solution in
pentane), and ca. 25 mg of bromobenzoquinone 6b9 to give 52
mg (83%) of a yellow oil: 1H NMR (CD2Cl2) δ 7.34 (d, J ) 2.9
Hz, 1H), 6.92 (dd, J ) 10.0, 2.9 Hz, 1H), 6.32 (dd, J ) 10.0, 1.0
Hz, 1H), 5.15 (dd, J ) 6.5, 2.5 Hz, 1H), 5.00 (m, 1H), 4.47 (m,
2H), 4.05 (m, 1H), 3.90 (m, 1H), 3.22 (s, 1H), 1.40 (s, 3H), 1.30
(s, 3H), 0.87 (s, 9H), 0.07 (“s”, 6H); 13C NMR (CD2Cl2) δ 177.9,
157.7, 147.5, 147.2, 132.8, 127.7, 109.1, 102.2, 86.4, 74.1, 73.6,
69.7, 65.8, 26.6, 25.9, 25.2, 18.3, -4.6, -4.9; FTIR (neat) 3388,
1674, 1066 cm-1; HRMS (FAB) calcd 485.0995, found 485.0990
(M - H).
Mon oa ceta te 2a . A 10-mg sample (0.022 mmol) of quinol
ketal glycal 11 was treated with 0.11 mL of BH3‚THF (1 M
solution in THF) in a procedure similiar to that for preparing
compound 1a (except temperature and time of reaction, see text)
to give 7 mg (70%) of a yellow oil: 1H NMR (CDCl3) δ 7.34 (d, J
) 7.1 Hz, 2H), 6.80 (d, J ) 7.0 Hz, 2H), 4.46 (d, J ) 1.7 Hz, 1H),
4.81 (d, J ) 1.6 Hz, 1H), 4.41 (m, 1H), 4.19 (m, 1H), 4.0 (dd, J
) 8.4, 2.0 Hz), 3.91 (dd, J ) 8.3, 2.8 Hz, 1H), 3.76 (m, 3H), 2.10
(s, 3H), 1.41 (s, 3H), 1.33 (s, 3H), 0.78 (s, 9H), 0.07 (s, 3H), -0.03
(s, 3H); 13C NMR (CDCl3) δ 170.0, 159.1, 132.0, 127.9, 113.5,
109.0, 86.1, 85.7, 84.0, 76.4, 72.3, 68.1, 55.3, 26.8, 25.6, 25.4,
21.1, 18.0, -5.0, -5.5; FTIR (neat) 1754, 1221, 1069 cm-1; HRMS
(FAB) calcd 467.2465, found 467.2458 (M + H).
Dia ceta te 2b. An 11-mg sample (0.027 mmol) of quinol glycal
12a was treated with 0.13 mL of BH3‚THF (1 M solution in THF)
in a procedure resembling that for making compound 2b (except
temperature and time of reaction, see text) to yield 7 mg (54%)
of a yellow oil: 1H NMR (CDCl3) δ 7.43 (d, J ) 6.8 Hz, 2H), 7.00
(d, J ) 6.6 Hz, 2H), 4.89 (dd, J ) 2.2, 1.4 Hz, 2H), 4.42 (m, 1H),
4.20 (m, 2H), 4.0 (dd, J ) 9.4, 6.3 Hz, 1H), 3.95 (dd, J ) 9.3, 5.7
Hz, 1H), 2.26 (s, 3H), 2.12 (s, 3H), 1.33 (s, 3H), 1.23 (s, 3H), 0.75
(s, 9H), 0.06 (s, 3H), -0.06 (s, 3H); 13C NMR (CDCl3) δ 170.3,
169.5, 127.2, 122.0, 109.1, 108.9, 99.6, 82.9, 79.9, 75.5, 73.1, 71.6,
67.8, 30.1, 26.8, 26.0, 25.8, 25.4, 18.3, -4.9, -5.2; FTIR (neat)
1748, 1234, 1069 cm-1; HRMS (FAB) calcd 435.2203, found
435.2199 (M - C4H3O2).
Dia ceta te 2c. A 24-mg sample (0.049 mmol) of bromoquinol
glycal 12b was treated with 0.25 mL of BH3‚THF (1 M solution
in THF) in a procedure similiar to that for preparing 2c (except
temperature and time of reaction) to give (after double elution
of a prep TLC plate with hexanes/EtOAc 3:1) 12 mg (43%) of a
yellow oil: 1H NMR (CDCl3) δ 7.81 (d, J ) 2.0 Hz, 1H), 7.53
(dd, J ) 1.9, 8.3 Hz, 1H), 7.10 (d, J ) 8.8 Hz, 1H), 4.95 (d, J )
3.9 Hz, 1H), 4.14 (m, 3H), 3.85 (m, 3H), 2.34 (s, 3H), 2.06 (s,
3H), 1.37 (s, 3H), 1.31 (s, 3H), 0.88 (s, 9H), 0.12 (s, 3H), 0.08 (s,
3H); 13C NMR (CDCl3) δ 170.3, 168.7, 157.0, 130.8, 130.2, 126.2,
124.0, 116.6, 109.0, 100.8, 85.9, 79.9, 74.6, 73.7, 66.4, 26.8, 26.0,
25.8, 25.4, 20.9, 18.4, -4.4, -4.8; FTIR (neat) 1772, 1191, 1069
cm-1; HRMS (FAB, NaI) calcd 597.1318, found 597.1314 (M +
Na, 81Br).
Ack n ow led gm en t. Funding for the synthesis of
C-aryl glycosides has been provided by the National
Cancer Institute (Grant No. CA50720) and the National
Science Foundation (CHE-9521055). We thank Drs.
J ames van Epp and Meng Chen for the assistance in
obtaining mass spectra.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
and infrared spectra for compounds 1, 2, 7, 11, and 12 (33
pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS, see any current
masthead page for ordering information.
J O951344O