Conversion of homoallylic alcohols with alkene protection to the corresponding methyl ketones

Full text of DOI:10.1021/jo9817725

J . Org. Chem. 1999, 64, 663-665
663
Ta ble 1. F or m a tion of 3 fr om 2 via In ter m ed ia tes 7, 8,
a n d 9
Con ver sion of Hom oa llylic Alcoh ols w ith
Alk en e P r otection to th e Cor r esp on d in g
Meth yl Keton es
yields (%)
compd
R1
R2
R3
7
8
9
3
Michael E. J ung,* Usama Karama, and
Rodolfo Marquez1
a
b
c
d
e
Me
Me
Me
CH2OTBS
CH2OTBS
Me
Ph
H
Me
Me
H
H
H
Bn
H
60
86
48
64
86
93
82
82
88
86
87
76
70
67
66
Department of Chemistry and Biochemistry, University of
California, Los Angeles, Los Angeles, California 90095-1569
52
Received August 31, 1998
successful attempt at protecting the alkene of 2 coupled
with selective oxidation, reductive ring opening, and final
conversion to the methyl ketone 3.
In the course of a total synthesis of the potent cytotoxic
agents tedanolide 1a and 13-deoxy-tedanolide 1b,2 a good
method was needed to carry out two specific transforma-
tions, namely, a reversible protection of the alkene of the
homoallylic alcohol system 2 and the conversion of the
homoallylic alcohol or ether into the methyl ketone 3.
Cyclization of either the homoallylic alcohols or the
corresponding benzyl ethers 2a -f to the bromotetrahy-
drofurans 7a -f was carried out (Table 1) by treatment
with N-bromosuccinimide (NBS) in dichloromethane to
give only one diastereomer of the desired products.5,6 This
Accordingly, it was necessary to protect the alkene
functionality in order to permit the application of a “non-
aldol aldol” process,3 thereby avoiding certain problems
associated with allylic epoxide rearrangements.4 For
example, when the oxirane 4 was treated with a silyl
triflate in the presence of base, the major product
obtained was the ketone 6 arising from cleavage of the
allylic oxirane C-O bond rather than the expected non-
aldol aldol product 5, which would have been formed by
cleavage of the tertiary oxirane C-O bond. To prevent
this undesirable rearrangement (to give 6 instead of 5),
the alkene had to be protected. Herein we describe our
diastereoselectivity can be explained by postulating that
bromination proceeds via addition of the positive bromine
to the bottom face of the alkene in conformation I with
the hydrogen “inside” with concomitant attack of the
oxygen on the top face (with loss of a proton or benzyl
cation)7 to give 7. The stereochemistry of the products
was proven rigorously for compounds 7d and 7f by
NOESY experiments (correlations shown below) and has
been assigned by analogy for 7a -c.
(1) UCLA President’s Fellow, 1994-1998. Awardee of Excellence for
First Year Graduate Study Award, 1995.
(2) (a) Fusetani, N.; Sugawara, T.; Matsunaga, S.; Hirota, H. J . Org.
Chem. 1991, 56, 4971. (b) Schmitz, F. J .; Gunasekera, S. P.; Yalaman-
chili, G.; Hossain, M. B.; van der Helm, D. J . Am. Chem. Soc. 1984,
106, 7251.
(3) J ung, M. E.; D’Amico, D. C. J . Am. Chem. Soc. 1993, 115, 12208.
(4) (a) J ung, M. E.; D’Amico, D. C. J . Am. Chem. Soc. 1995, 117,
7379. (b) J ung, M. E.; D’Amico, D. C. J . Am. Chem. Soc. 1997, 119,
12150. (c) J ung, M. E.; Anderson, K. L. Tetrahedron Lett. 1997, 38,
2605.
(5) For a good review of cyclizations of this type, see: Harding, K.
E.; Tiner, T. H. Electrophilic Heteroatom Cyclizations. In Comprehen-
sive Organic Synthesis; Trost, B. M., Ed.; Pergamon: Oxford, 1991;
Vol. 4, Chapter 1.9, p 363.
(6) For an example of this less common 5-endo cyclization, see:
Mihailovic, M. Lj.; Marinkovic, D. J . Serb. Chem. Soc. 1985, 50, 5.
(7) For examples of the loss of an alkyl cation in electrophilic
cyclizations, see: (a) Parker, K. A.; O’Fee, R. J . Am. Chem. Soc. 1983,
105, 654. (b) Rychnovsky, S. D.; Bartlett, P. A. J . Am. Chem. Soc. 1981,
103, 3963. (c) See also ref 5.
10.1021/jo9817725 CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/05/1999

664 J . Org. Chem., Vol. 64, No. 2, 1999
Notes
used. The infrared (IR) spectra were recorded on a Fourier
transform IR spectrometer.
Having protected the alkene as a bromo ether, further
transformations of the R1 group were possible. To regen-
erate the alkene and eventually to prepare the desired
methyl ketone, we decided to oxidize the tetrahydro-
furans 7 to the lactones 8. This was accomplished using
RuCl3 and NaIO48 in the preferred mixed solvent system9
to give 82-93% yields of the desired lactones. Reductive
ring opening was then effected with zinc dust in aqueous
ethanol to give the alkenoic acids 9 in 70-87% yield.
Simple reduction of the bromotetrahydrofurans 7 to
regenerate the homoallylic alcohols was unsuccessful
with zinc or a variety of other reducing agents, although
it was cleanly carried out with tert-butyllithium. Finally,
the acids 9, on treatment with lithium dimethylcuprate,
were converted to the methyl ketones via their crude acid
chlorides (prepared by reaction with oxalyl chloride) to
give 3 in 52-67% yield.
Gen er a l P r oced u r e for th e P r ep a r a tion of th e 3-P en -
ten oic Acid s, 9. Excess zinc dust was suspended in ethanol
containing a small amount of water. The zinc suspension was
treated with a solution of lactone 8 (0.4-1.0 mmol) in ethanol
(4 mL). The mixture was refluxed for 5 h and cooled to room
temperature. Insoluble particles were filtered through Celite.
The filtrate was concentrated in vacuo and extracted with diethyl
ether (2 × 20 mL). The organic phase was extracted with 10%
Na2CO3 (2 × 20 mL), followed by acidification with cold
concentrated HCl and subsequent extraction with diethyl ether
(4 × 50 mL). The organic phases were washed with brine (30
mL), dried over MgSO4, and vacuum concentrated to give the
3-pentenoic acid 9.
2,4-Dim eth yl-3-p en ten oic a cid , 9a . Zinc dust (3.14 g, 48
mmol) and 8a (191 mg, 1.0 mmol) gave 110 mg (86%) of the
known carboxylic acid 9a . The spectroscopic data for 9a matched
that reported in the literature.11
4-Meth yl-2-p h en yl-3-p en ten oic Acid , 9b. Zinc dust (4.71
g, 72 mmol) and lactone 8b (380 mg, 1.50 mmol) gave 249 mg
1
(87%) of carboxylic acid 9b. H NMR (CDCl3, 200 MHz) δ: 7.40
(5Η, m), 5.53 (1Η, dm, J ) 9.4 Hz), 4.49 (1H, d, J ) 9.4 Hz),
1.67 (3H, d, J ) 1.1 Hz), 1.59 (3H, d, J ) 1.3 Hz). 13C NMR
(CDCl3, 50 MHz) δ: 179.16, 138.87, 135.71, 128.70, 127.90,
127.20, 121.39, 50.42, 25.86, 25.74. IR (neat): 3500-3100 (br),
2978, 2928, 2856, 1736, 1456, 1116 cm-1
.
4-Meth yl-3-p en ten oic Acid , 9c. Zinc dust (1.30 g, 19.8
mmol) and lactone 8c (80 mg, 0.414 mmol) gave 36 mg (76%) of
the known carboxylic acid 9c. 1H NMR (CDCl3, 200 MHz) δ:
10.59 (1Η, bs), 5.21 (1Η, tm, J ) 7.1 Hz), 2.98 (2H, d, J ) 7.2
Hz), 1.67 (3H, s), 1.56 (3H, s). 13C NMR (CDCl3, 50 MHz) δ:
178.85, 136.12, 115.11, 33.53, 25.56, 25.24. IR (neat): 3450-
3100 (br), 2968, 2924, 1708, 1414, 1302, 1221, 1155 cm-1
.
(3E)-2,4-Dim eth yl-5-[((1,1-d im eth yleth yl)d im eth ylsilyl)-
oxy]-3-p en ten oic Acid , 9d . Zinc dust (3.14 g, 48 mmol) and
lactone 8d (300 mg, 0.89 mmol) gave 160 mg (70%) of carboxylic
acid 9d . 1H NMR (CDCl3, 200 MHz) δ: 5.38 (1Η, dm, J ) 9.4
Hz), 3.97 (2Η, s), 3.33 (1H, m), 1.59 (3H, d, J ) 1.1 Hz), 1.19
(3H, d, J ) 7.0 Hz), 0.94 (9H, s), 0.02 (6H, s). 13C NMR (CDCl3,
50 MHz) δ: 181.23, 137.27, 122.72, 67.96, 38.33, 25.89, 18.37,
17.63, 13.58 (two high-field carbons not recorded). IR (neat):
We have thus shown that bromoetherification of ho-
moallylic alcohols and ethers occurs diastereoselectively
to give bromotetrahydrofurans (where the alkene func-
tionality has been protected), which are cleanly oxidized
to the lactones, reduced to the alkenoic acids, and
converted into the desired methyl ketones. Further work
on the “non-aldol aldol” process and the synthesis of the
tedanolides will be reported in due course.10
2939, 2893, 2860, 1713, 1464, 1253, 1082, 815, 777 cm-1
.
Gen er a l P r oced u r e for th e Con ver sion of th e Acid 9
in to th e 4-Hexen -2-on e, 3. A solution of the acid 9 (0.5-1
mmol) in methylene chloride was treated with a 2 M oxalyl
chloride solution in methylene chloride. After the mixture had
stirred for 4 h at room temperature, it was concentrated under
vacuum to produce the crude acid chloride, which was dissolved
in THF and added at -78 °C to a THF solution of lithium
dimethylcuprate, previously prepared by addition of 1 M meth-
yllithium (2 equiv) to a suspension of copper(I) iodide (1 equiv)
in THF at 0 °C and stirred at room temperature for 10 min.
After the THF solution had stirred for 1 h, the reaction was
quenched by the sequential addition of methanol and saturated
NH4Cl at -78 °C. The organic phase was removed under
vacuum. The remaining aqueous phase was extracted with
diethyl ether, dried over MgSO4, and purified by flash column
chromatography (silica gel, 50% diethyl ether:hexanes) to give
the enone 3.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out under
argon with the exclusion of moisture. Reagents were purchased
from commercial sources and used without further purification
unless otherwise specified. The following solvents and reagents
were distilled from the indicated agent under argon: tetrahy-
drofuran (THF) and diethyl ether from sodium benzophenone
ketyl; dichloromethane, benzene, and toluene from calcium
hydride; triethylamine from calcium hydride. Flash column
chromatography was carried out in the indicated solvent system
on 230-400 mesh silica gel. The proton nuclear magnetic
resonance (1H NMR) spectra were recorded at 200 and 500 MHz,
and the carbon nuclear magnetic resonance (13C NMR) spectra
were recorded at 50 and 125 MHz. Spectra were taken in the
indicated solvent at ambient temperature, and the chemical
shifts are reported in parts per million relative to the solvent
3,5-Dim eth yl-4-h exen -2-on e, 3a . The acid 9a (100 mg, 0.780
mmol) gave 66 mg (67%) of the known enone 3a . The spectro-
scopic data for 3a matched that reported in the literature.12
5-Meth yl-3-p h en yl-4-h exen -2-on e, 3b. The acid 9b (200 mg,
1.05 mmol) gave 130 mg (66%) of compound 3b. 1H NMR (CDCl3,
200 MHz) δ: 7.25 (5H, m), 5.62 (1H, dm, J ) 9.4 Hz), 4.52 (1H,
d, J ) 9.4 Hz), 2.08 (3H, s), 1.76 (3H, d, J ) 0.9 Hz), 1.69 (3H,
d, J ) 1.3 Hz). 13C NMR (CDCl3, 50 MHz) δ: 207.14, 139.26,
135.43, 128.85, 128.05, 127.01, 121.53, 58.82, 28.27, 25.98, 18.24.
IR (neat): 2972, 2914, 2860, 1716, 1601, 1493, 1354, 1155, 750,
700 cm-1
.
(8) Smith, A. B., III; Scarborough, R. M. Synth. Commun. 1980, 10,
205.
(9) Carlsen, P. H. J .; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J .
Org. Chem. 1981, 46, 3936.
(10) (a) J ung, M. E.; Lee, W. S. Manuscript submitted for publica-
tion. (b) J ung, M. E.; Marquez, R. Manuscript submitted for publica-
tion.
(11) Henin, F.; Mortezaei, R.; Muzart, J .; Pete, J .-P.; Piva, O.
Tetrahedron 1989, 45, 6171.
(12) Van der Weerdt, A. J . A.; Cerfontain, H. J . Chem. Soc., Perkin
Trans. 2 1977, 1357.

Notes
3,5-Dim eth yl-6-h yd r oxy-4-h exen -2-on e, 3d . The acid 9d
J . Org. Chem., Vol. 64, No. 2, 1999 665
dimethylsilyl)oxy]pent-3-en-1-ol, 2f (42.7 mg, 0.187 mmol),
(130 mg, 0.503 mmol) gave 37 mg (52%) of compound 3d . 1H
NMR (CDCl3, 200 MHz) δ: 5.30 (1H, dm, J ) 9.7 Hz), 3.98 (2H,
s), 3.38 (1H, m), 2.08 (3H, s), 1.68 (3H, d, J ) 1.2 Hz), 1.10 (3H,
d, J ) 6.3 Hz). 13C NMR (CDCl3, 50 MHz) δ: 209.98, 137.65,
124.49, 68.15, 46.59, 27.97, 16.46, 14.02. IR (neat): 3427, 2974,
yielded 49 mg (86%) of compound 7f: [R]25 ) -36.74° (c 1.87
D
in CHCl3). 1H NMR (CHCl3, 500 MHz) δ: 4.11 (1H, app t, J )
8.3 Hz), 3.81 (1H, d, J ) 10.7 Hz), 3.58 (1H, d, J ) 10.7 Hz),
3.52 (1H, d, J ) 10.4 Hz), 3.41 (1H, dd, J ) 8.5, 8.2 Hz), 2.82
(1H, m), 1.20 (3H, s), 1.09 (3H, d, J ) 6.7 Hz), 0.90 (9H, s), 0.07
(3H, s), 0.06 (3H, s). 13C NMR (CDCl3, 125 MHz) δ: 83.71, 72.73,
68.39, 60.90, 42.33, 25.76, 21.65, 18.13, 15.50, -5.66 (2C’s). IR
(neat): 2959, 2930, 2858, 1471, 1462, 1361, 1251, 1109, 1032,
2930, 2872, 1709, 1456, 1356 cm-1
.
Gen er a l P r oced u r e for th e F or m a tion of th e 3-Br o-
m otetr a h yd r ofu r a n s, 7. The 3-penten-1-ol 2 (1 equiv) was
dissolved in anhydrous methylene chloride. N-Bromosuccinimide
(NBS, 2 equiv) was added, and the mixture was refluxed in the
dark for 8 h. The solvent was evaporated, pentane was added,
and the suspension was filtered. The filtrate was concentrated
under vacuum. It was flash column chromatographed (silica gel,
20% diethyl ether:hexanes) to yield the bromotetrahydrofuran
7.
942, 839, 777 cm-1
.
Gen er a l P r oced u r e for th e F or m a tion of th e 4-Br o-
m od ih yd r ofu r a n -2(3H)-on es, 8. A mixture of the 3-bromotet-
rahydrofuran 7 (1 equiv), RuCl3‚H2O (0.55 equiv), and NaIO4 (8
equiv) in a solvent mixture of 1:1:1.5 carbon tetrachloride,
acetonitrile, and water was stirred at room temperature for 14
h. The reaction mixture was treated with 2-propanol and was
stirred vigorously for an additional 1 h. The mixture was
extracted with methylene chloride. The combined organic phases
were dried over MgSO4. After evaporation of the solvent, diethyl
ether was added and the suspension was filtered through Celite.
The solvent was removed under vacuum to produce a crystalline
solid which, upon washing with cold pentane, yielded the
bromolactones 8.
tr a n s-3-Br om o-2,2,4-tr im eth yltetr a h yd r ofu r a n , 7a . 2,4-
Dimethyl-3-penten-1-ol, 2a (400 mg, 3.50 mmol), gave 406 mg
(60%) of compound 7a . 1H NMR (CDCl3, 200 MHz) δ: 3.95 (1H,
app t, J ) 8.5 Hz), 3.42 (1H, d, J ) 8.7 Hz), 3.32 (1H, t, J ) 8.7
Hz), 2.45 (1H, m), 1.25 (3H, s), 1.22 (3H, s), 1.09 (3H, d, J ) 6.6
Hz). 13C NMR (CDCl3, 50 MHz) δ: 82.21, 70.96, 62.25, 41.99,
26.19, 23.98, 15.40. IR (neat): 2974, 2934, 2876, 1593, 1458,
1388, 1136, 1028, 804, 699 cm-1
.
t r a n s-4-B r o m o d ih y d r o -3,5,5-t r im e t h y lfu r a n -2(3H )-
on e, 8a . 3-Bromo-2,2,4-trimethyltetrahydrofuran, 7a (130 mg,
0.67 mmol), yielded 120 mg (93%) of compound 8a . 1H NMR
(CDCl3, 200 MHz) δ: 3.76 (1H, d, J ) 11.7 Hz), 2.80 (1H, dd, J
) 11.7, 6.9 Hz), 1.44 (6H, bs), 1.28 (3H, d, J ) 7.0 Hz). 13C NMR
(CDCl3, 50 MHz) δ: 174.38, 84.47, 56.36, 43.60, 26.00, 23.63,
tr a n s-3-Br om o-2,2-d im et h yl-4-p h en ylt et r a h yd r ofu r a n ,
7b. 4-Methyl-2-phenyl-3-penten-1-ol, 2b (1.4 g, 7.95 mmol), gave
1.75 g (86%) of compound 7b. 1H NMR (CDCl3, 500 MHz) δ: 7.30
(5H, m), 4.24 (1H, app t, J ) 9.1 Hz), 3.92 (1H, d, J ) 10.3 Hz),
3.88 (1H, app t, J ) 8.7 Hz), 3.65 (1H, m), 1.42 (3H, s), 1.41
(3H, s). 13C NMR (CDCl3, 125 MHz) δ: 138.86, 128.72, 127.34,
82.87, 71.31, 62.00, 53.46, 25.87, 23.35 (one low field carbon
unresolved). IR (neat): 2976, 2930, 2878, 1601, 1369, 1136, 1032,
12.41. IR (neat): 3057, 2986, 1780, 1265, 1109, 738, 704 cm-1
.
tr a n s-4-Br om od ih yd r o-5,5-d im et h yl-3-p h en ylfu r a n -2-
(3H)-on e, 8b. 3-Bromo-2,2-dimethyl-4-phenyltetrahydrofuran,
7b (1.70 g, 6.66 mmol), yielded 1.38 g (82%) of compound 8b.
1H NMR (CDCl3, 200 MHz) δ: 7.30 (5H, m), 4.20 (1H, d, J )
11.9 Hz), 4.01 (1H, d, J ) 11.9 Hz), 1.61 (3H, s), 1.58 (3H, s).
13C NMR (CDCl3, 50 MHz) δ: 162.20, 133.39, 129.03, 128.55,
128.44, 84.65, 57.06, 55.00, 26.10, 24.06. IR (neat): 2959, 2924,
698 cm-1
.
3-Br om o-2,2-d im eth yltetr a h yd r ofu r a n , 7c. 4-Methyl-3-
penten-1-ol, 2c (250 mg, 2.50 mmol), gave 216 mg (48%) of the
known bromo furan compound 7c. The spectroscopic data for
7c matched that reported in the literature.6
2853, 1753, 1456, 1375, 1259, 1095, 734, 698 cm-1
.
tr a n s-3-Br om o-2,4-d im et h yl-2-[((1,1-d im et h ylet h yl)d i-
m et h ylsilyl)oxy]m et h ylt et r a h yd r ofu r a n , 7d . (3E)-2,4-Di-
methyl[((1,1-dimethylethyl)dimethylsilyl)oxy]-5-(phenylmethoxy)-
2-pentene, 2d (1.00 g, 2.99 mmol), was dissolved in anhydrous
methylene chloride (80 mL). NBS (1.05 g, 5.98 mmol) was added,
and the mixture was refluxed in the dark for 5 days. The solvent
was evaporated, pentane (25 mL) was added, and the suspension
was filtered. The filtrate was concentrated under vacuum. It was
flash column chromatographed (silica gel, 2.5% diethyl ether:
hexanes) to yield 620 mg (64%) of compound 7d . The spectro-
scopic data for this compound matched that of the optically active
compound prepared from 2e as described below.
4-Br om od ih yd r o-5,5-d im eth ylfu r a n -2(3H)-on e, 8c. 3-Bro-
mo-2,2-dimethyltetrahydrofuran, 7c (650 mg, 3.63 mmol), yielded
574 mg (82%) of compound 8c. 1H NMR (CDCl3, 200 MHz) δ:
4.28 (1H, t, J ) 7.4 Hz), 3.16 (1H, dd, J ) 18.1, 7.5 Hz), 2.87
(1H, dd, J ) 18.1, 7.3 Hz), 1.59 (3H, s), 1.49 (3H, s). 13C NMR
(CDCl3, 50 MHz) δ: 173.50, 86.35, 49.62, 39.83, 25.88, 25.29.
IR (neat): 2984, 2928, 2855, 1786, 1464, 1275, 1122, 611 cm-1
.
(3R ,4S ,5R )-4-Br om od ih yd r o-3,5-d im e t h yl-5-[((1,1-d i-
m eth yleth yl)d im eth ylsilyl)oxy]m eth ylfu r a n -2(3H)on e, 8d .
(2R,3S,4R)-3-Bromo-2,4-dimethyl-2-[((1,1-dimethylethyl)dimeth-
ylsilyl)oxy]methyltetrahydrofuran, 7d (350 mg, 1.083 mmol),
yielded 320 mg (88%) of compound 8d . 1H NMR (CDCl3, 200
MHz) δ: 4.26 (1H, d, J ) 11.6 Hz), 3.68 (1H, d, J ) 11.7 Hz),
3.57 (1H, d, J ) 11.7 Hz), 2.77 (1H, m), 1.34 (3H, s), 1.26 (3H,
d, J ) 7.0 Hz), 0.82 (9H, s), 0.07 (3H, s), 0.06 (3H, s).13C NMR
(CDCl3, 50 MHz) δ: 174.29, 86.03, 64.60, 49.34, 43.55, 25.73,
19.78, 18.17, 12.48, (two high-field carbons not recorded). IR
(neat): 2955, 2885, 2858, 1788, 1461, 1311, 1120, 949, 839, 779,
(2R,3S,4R)-3-Br om o-2,4-dim eth yl-2-[((1,1-dim eth yleth yl)-
d im eth ylsilyl)oxy]m eth yltetr a h yd r ofu r a n , 7d . (3E,2S)-2,4-
Dimethyl-5-[((1,1-dimethylethyl)dimethylsilyl)oxy]pent-3-en-1-
ol, 2e (124.4 mg, 0.546 mmol), was dissolved in anhydrous
methylene chloride (18 mL). After addition of NBS (214 mg, 1.20
mmol), the mixture was refluxed in the dark for 1.5 h. Water
was added, and the layers were separated, with subsequent
washing of the aqueous layer with methylene chloride (15 mL).
Combining of the organic layers, followed by drying (MgSO4),
concentration under vacuum, and flash column chromatography
(silica gel, 4% ethyl acetate in hexanes), yielded 146.7 mg (88%)
613 cm-1
.
Ack n ow led gm en t. We acknowledge financial sup-
port of the National Institutes of Health (CA72684).
of compound 7d : [R]25 ) -12.88° (c 0.73 in CHCl3). 1H NMR
D
(C6D6, 500 MHz) δ: 4.07 (1H, d, J ) 10.7 Hz), 3.69 (1H, app t,
J ) 8.1 Hz), 3.54 (1H, d, J ) 10.8 Hz), 3.52 (1H, d, J ) 10.8 Hz),
3.18 (1H, dd, J ) 10.0, 8.3 Hz), 2.26 (1H, m), 1.26 (3H, s), 0.96
(9H, s), 0.84 (3H, d, J ) 6.52 Hz), 0.07 (3H, s), 0.06 (3H, s). 13C
NMR (CDCl3, 125 MHz) δ: 84.19, 72.09, 66.60, 56.32, 42.13,
25.76, 21.64, 18.15, 14.08, -5.46, -5.64. IR (neat): 2957, 2930,
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of all new compounds and the NOESY data for
compounds 7d and 7f (30 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.
2856, 1460, 1381, 1251, 1103, 1037, 925, 837, 814, 777 cm-1
.
(2S,3S,4R)-3-Br om o-2,4-d im eth yl-2-[((1,1-d im eth yleth yl)-
d im eth ylsilyl)oxy]m eth yltetr a h yd r ofu r a n , 7f. By an analo-
gous procedure, (3Z,2S)-2,4-dimethyl-5-[((1,1-dimethylethyl)-
J O9817725