Synthesis of C1-C6 segment of carbonolide B: Wolff rearrangement of sugar α-diazo ketones

Article abstract of DOI:10.1055/s-2000-6343

Silver benzoate catalysed Wolff rearrangement of a series of α-diazo ketones, derived from furanuronic acids, in methanol proceeds with good yields to produce the corresponding one carbon homologated methyl-5-deoxy- hexo-furanuronate. The utility of methy

Full text of DOI:10.1055/s-2000-6343

PAPER
395
Synthesis of C1-C6 Segment of Carbonolide B: Wolff Rearrangement of Sugar
a-Diazo Ketones
Jayant N. Tilekar, Nitin T. Patil, Dilip D. Dhavale*
Garware Research Centre, Department of Chemistry, University of Pune, Pune - 411 007, India
E-mail: ddd@chem.unipune.ernet.in
Received 21 October 1999
to 4a (free from its C4 epimer) (Scheme 1). The com-
Abstract: Silver benzoate catalysed Wolff rearrangement of a se-
pound 5a in turn could be readily obtained from D-glu-
ries of a-diazo ketones, derived from furanuronic acids, in methanol
cose.
proceeds with good yields to produce the corresponding one carbon
homologated methyl-5-deoxy-hexo-furanuronate. The utility of
methyl-1,2-O-isopropylidene-3-O-methyl-5-deoxy-a-D-xylo-hexo-
furanuronate was demonstrated in the synthesis of the right wing
segment of carbonolide B - the aglycone of the 16 membered mac-
rolide antibiotic carbomycin B.
Key words: a-diazo ketones, Wolff rearrangement, macrolide anti-
biotics, carbomycin, carbonolide
Carbomycin B (magnamycin B), tylosin and josamycin
(leucomycin A3) constitute the medicinally important 16-
membered macrolide antibiotics. The structural aspects,
intriguing configurational features, and potential biologi-
cal properties of these macrolide antibiotics have been the
subject of synthetic studies over the years. This has result-
ed in a number of carbohydrate,1 as well as non-
carbohydrate2 based convergent syntheses of carbonolide
B 1 (the aglycone portion of carbomycin B). Examination
of the right hand portion of 1 shows the C1-C9 segment 2
which could be obtained by the Michael addition of lithi-
um methallyl cuprate to the a,b-unsaturated ester 3
(Scheme 1). The key intermediate for the formation of 3
is methyl-a-D-xylo-hexo-furanuronate 4a (upon hydroly-
sis of 1,2-O-isopropylidene functionality followed by
Wittig olefination) which represents the C1-C6 carbon
framework of 1 and could be derived from D-glucose. The
presence of three contiguous stereogenic centers from C3
Scheme 1
to C5 with hydroxyl functionalities makes the carbohy-
drate route more appropriate for its synthesis. Only two
chiron approaches for 4a are known so far. The first strat-
In recent years, the utility of a-diazocarbonyl derivatives
either via carbene generation or through Wolff rearrange-
ment has attracted considerable attention from both the
synthetic and the mechanistic point of view.5 The impor-
tant synthetic application of the Wolff rearrangement is
the Arndt−Eistert synthesis for one carbon homologation
of carboxylic acids.6 The fact that the rearrangement pro-
ceeds with the retention of configuration at the asymmet-
ric carbon next to the carbonyl group is advantageous in
exploiting the reaction sequence with chiral substrates.
Although, this approach has been widely exploited in the
syntheses of a number of optically pure compounds,7 its
utility for sugar substrates is highly restricted. To our
knowledge, only one unsuccessful report is available8
wherein, the Wolff rearrangement of 3,4,5,6,7-penta-O-
egy reported by Nicolaou3 involves the multi-step synthe-
sis of 5,6-dideoxy-3-O-methyl-1,2-O-isopropylidene-a-
D-xylo-hexo-5-eno-furanose from D-glucose followed by
hydroboration and oxidative workup with H2O2/NaOH to
give
5-deoxy-3-O-methyl-1,2-O-isopropylidene-a-D-
xylo-hexo-furanose. Oxidation of the primary alcohol to
the acid and esterification with diazomethane afforded 4a.
While, in the second route4 4a (along with its C4 epimer)
was derived from the 5,6-dideoxy-6-flouro-6-(N-methyl-
N-phenyl)-5,6-enamino-3-O-methyl-1,2-O-isopropylid-
ene-a-D-xylo-hexo-furanose by reaction with 5% HCl in
methanol. Although, the first route has wide utility, the
second approach has very limited synthetic applications.
It occurred to us that the Wolff rearrangement of sugar de-
rived a-diazo ketone 5a in methanol should lead directly
Synthesis 2000, No. 3, 395–398 ISSN 0039-7881 © Thieme Stuttgart · New York

396
J. N. Tilekar et al.
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acetyl-1-deoxy-1-diazo-D-gluco-heptulose led to the for- action after six days afforded the expected rearranged
mation of an unsaturated acid namely trans-4,5,6,7-tetra- product 4a with retention of configuration at C4 but in low
O-acetyl-2,3-dideoxy-D-arabino-hept-2-enonic acid and yield (37%). Attempts were made to optimise the reaction
not the expected saturated b-acetoxy acid. As a part of our conditions by variation in the amounts of silver benzoate.
continuing interest in the synthesis of biologically active Better results in a short period were obtained with 0.3 mo-
compounds,9 we have investigated the Wolff rearrange- lar equivalents of silver benzoate, which resulted in the
ment of sugar derived α-diazo ketones 5a-d and our re- formation of 4a in 78% yield. Having synthesized the ex-
sults are reported herein.
pected chiral synthon 4a in good yield, the methodology
was extended to the sugar a-diazo ketones 5b and 5c, pre-
pared from the 6b and 6c respectively, which on Wolff re-
arrangement led to the corresponding rearranged products
4b and 4c. While elaborating the strategy for the D-man-
nose derived a-diazo ketone 5d; the treatment of oxalyl
chloride with α-D-lyxo-furanuronic acid 6d, under our and
reported10 conditions followed by diazomethane gave the
methyl ester of α-D-lyxo-furanuronic acid in 65% yield
along with the expected sugar a-diazo ketone 5d in low
yield (28%). Modification of the reaction conditions using
Seebach’s procedure11 wherein 6d was first reacted with
ethyl chloroformate in the presence of Et3N in THF and
then treated with diazomethane in diethyl ether afforded
5d in good yield. The Wolff rearrangement of 5d, as stat-
ed above, gave 4d in good yield (Scheme 2).
The requisite substrates namely furanuronic acids 6a-d
were easily obtained by the usual methods from D-glucose
and D-mannose as reported by us and others earlier.10 In
the initial studies, 1,2-O-isopropylidene-3-O-methyl-a-D-
xylo-hexo-furanuronic acid 6a was converted to the acid
chloride by treatment with oxalyl chloride in dichlo-
romethane (Scheme 2). The acid chloride was immediate-
ly reacted with diazomethane in diethyl ether to afford the
a-diazo ketone 5a. The relatively unstable 5a was then
subjected to the conditions of Wolff rearrangement using
0.12 molar equivalents of silver benzoate, as the catalyst
in the presence of triethylamine in dry methanol. The re-
As shown in Scheme 1, compound 4a contains the appro-
priate functionalities along with the required stereochem-
istry of the hydroxyl groups for elaboration to the C1-C9
segment of the carbonolide B. Thus, hydrolysis of the 1,2-
O-isopropylidene functionality of 4a with TFA:H2O fol-
lowed by Wittig olefination with triphenyl ethoxycarbon-
ylmethylene phosphorane in toluene gave the required
a,b-unsaturated ester 3 in 80% yield. The 1H NMR spectra
and analytical data of 3 was in consonance with the data
reported in the literature.3
In conclusion, the Wolff rearrangement of a-diazo ke-
tones 5a-d is a mild and convenient method for the syn-
thesis of one carbon homologated esters 4a-d. The utility
of 4a was demonstrated in the synthesis of the right wing
portion of carbonolide B, which is of medicinal impor-
tance. The easy availability of furanuronic acids in gram
scale from the corresponding monosaccharide units
makes this route attractive. The potentiality of 4a-d was
also envisioned in the synthesis of rare sugars. For exam-
ple, 2-deoxy-L-sugars could be easily obtained by the
cleavage of 1,2-O-isopropylidene functionality followed
by NaBH4 reduction. Further applications in this direction
and structurally diverse natural products are in progress.
1H NMR spectra of CDCl3 solutions were recorded with a Bruker
AMX 500 MHz and a Varian VXR 300S MHz spectrometer. Chem-
ical shifts are reported in ppm (d) relative to TMS. IR spectra were
recorded with a Perkin−Elmer 1600 FT/IR spectrophotometer. Op-
tical rotations were measured at 25 °C with a Perkin−Elmer 241 po-
larimeter. Analyses (C, H) were performed on a Hosli carbon-
hydrogen analyser. Mps were measured on a Thomas−Hoover cap-
illary melting point apparatus and are uncorrected. All the reactions
were conducted in oven-dried glassware under dry N2. TLC was
carried out on Polygram Sil G/UV 254 precoated plastic sheets and
column chromatography was carried out using silica gel (100−200
mesh) with petroleum ether (bp 60−80 °C)/EtOAc as eluent. Silver
Reagents and conditions: i) Oxalyl chloride (1.2 equiv), DMF, (1
drop), CH2Cl2, 0−25 °C, 3 h; ii) CH2N2 (3 equiv), Et2O, 0−25 °C, 3 h;
iii) PhCOOAg (0.3 equiv), Et3N (6 equiv), MeOH, 0−25 °C, 3 h; iv)
TFA/H2O, 3:2, 0−25 °C, 2 h; v) Ph3P=CHCOOEt (1.2 equiv), tolu-
ene, 16 h, 25 °C; vi) ClCOOEt (1.1 equiv), Et3N (1.1 equiv), THF, 0
°C, 30 min
Scheme 2
Synthesis 2000, No. 3, 395–398 ISSN 0039-7881 © Thieme Stuttgart · New York

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Synthesis of C1-C6 Segment of Carbonolide B
397
benzoate was prepared as reported.12 Toluene, CH2Cl2, MeOH,
THF and Et2O were dried according to standard procedures. The re-
quired a-D-xylo-furanuronic acids 6a-c and a-D-lyxo-furonuronic
acid 6d were prepared according to our previous report.10
dropwise. The mixture was stirred for 1.5 h during which the tem-
perature slowly rose to r.t. The solvent was removed under reduced
pressure and the residue was purified by column chromatography
(petroleum ether/EtOAc, 15:1) to give 5d as a white solid. Yield:
0.90 g, 83%; mp 126−128 °C; [α]D25 -59.46 (c 1, CHCl3).
1,2-O-Isopropylidene-3-O-methyl-6-deoxy-6-diazo-a-D-xylo-
hexo-furan-5-ulose (5a); Typical Procedure
IR (nujol): ν = 2116 (CHN2), 1621 (C=O) cm−1.
To a stirred and cooled (0 °C) solution of a-D-xylo-furanuronic acid
6a (1 g, 4.5 mmol) in anhyd CH2Cl2 (15 mL) was added oxalyl chlo-
ride (0.48 mL, 5.5 mmol) and DMF (0.02 mL) under N2 atm. The
mixture was allowed to attain r.t. (25 °C) and stirred for 3 h. The
solvent was removed under reduced pressure and the acyl chloride
thus obtained was used in the next step. A solution of acyl chloride
in anhyd Et2O (10 mL) was cooled to 0 °C. To this an ice-cooled
solution of diazomethane (18 mmol) in Et2O (25 mL) was added
dropwise. The mixture was stirred for 2 h during which the temper-
ature slowly attained r.t. (30 °C). The solvent was removed under
reduced pressure and the residue was purified by column chromato-
graphy on silica gel (petroleum ether/EtOAc, 20:1) to give 5a as a
solid. Yield: 0.84 g, 76%; mp 141−142 °C; [α]D −173.63 (c 1,
CHCl3).
IR (nujol): ν = 2126 (CHN2), 1620 (C=O) cm-1.
1H NMR (300 MHz, CHCl3): δ = 1.33 (s, 3H, CH3), 1.48 (s, 3H,
CH3), 3.40 (s, 3H, OCH3), 4.08 (d, 1H, J = 3.6 Hz, C3-H), 4.58 (d,
1H, J = 3.7 Hz, C2-H), 4.68 (br d, 1H, J = 3.6 Hz, C4-H), 5.81 (br
s, 1H, CHN2), 5.99 (d, 1H, J = 3.7 Hz, C1-H).
1H NMR (200 MHz, CDCl3): δ = 1.29 (s, 3H, CH3), 1.45 (s, 3H,
CH3), 4.50 (d, 1H, J = 12 Hz, OCH2Ph), 4.55 (d, 1H, J = 4.0 Hz, C2-
H), 4.66 (d, 1H, J = 6.0 Hz, C4-H), 4.70 (d, 1H, J = 12.0 Hz,
OCH2Ph), 5.02 (dd, 1H, J = 6.0, 4.0 Hz, C3-H), 5.19 (s, 1H, C1-H),
5.78 (br s, 1H, CHN2), 7.27−7.50 (s, 5H, Ar-H).
Anal: C16H18N2O5 (318.32): Calc C, 60.37; H 5.70. Found C, 60.17;
H, 5.85.
5-Deoxy-3-O-methyl-1,2-O-(1-methylethylidene)-α-D-xylo hex-
ofuranuronic Acid Methyl Ester (4a); Typical Procedure
To a solution of α-diazo ketone 5a(0.75 g, 3.1 mmol) in anhyd
MeOH (12 mL) was added dropwise a solution of silver benzoate
(150 mg, 0.62 mmol) in Et3N (1.5 mL) at r.t. (25 °C) under N2 atm.
The mixture was stirred at the same temperature for 2.5 h. The sol-
vent was then removed under reduced pressure and the residue was
purified by column chromatography (petroleum ether/EtOAc, 15:1)
to give 4a as a colorless liquid. Yield: 0.59 g, 78%; [α]D25 −70.29 (c
1, CHCl3), [α]D25 −46.23 (c 1, MeOH), [Lit3a -45.89 (c 1, MeOH)].
25
IR (nujol): ν = 1738 (C=O) cm−1.
1H NMR (300 MHz, CDCl3): δ = 1.32 (s, 3H, CH3), 1.51 (s, 3H,
CH3), 2.75 (d, 2H, J = 7.0 Hz, CH2), 3.39 (s, 3H, OCH3), 3.70 (s,
3H, OCH3), 3.79 (d, 1H, J = 3.3 Hz, C3-H), 4.56 (dt, 1H, J = 7.0,
3.3 Hz C4-H), 4.59 (d, 1H, J = 4.0 Hz, C2-H), 5.87 (d, 1H, J = 4.0
Hz, C1-H).
Anal: C10H14N2O5 (242.23): Calc C, 49.58; H, 5.83. Found C,
49.70; H, 5.85.
1,2-O-Isopropylidene-3-O-benzyl-6-deoxy-6-diazo-a-D-xylo-
hexo-furan-5-ulose (5b)
White solid; yield: 0.91 g, 84%; mp 84−86 °C; [α]D25 −153.0 (c 1,
CHCl3).
Anal: C11H18O6 (246.25): Calc C, 53.65; H, 7.37. Found C, 53.52;
H, 7.60.
IR (nujol): ν = 2117 (CHN2), 1616 (C=O) cm−1.
5-Deoxy-3-O-benzyl-1,2-O-(1-methylethylidene)-α-D-xylo-
hexo-furanuronic Acid Methyl Ester (4b)
1H NMR (300 MHz, CHCl3): δ = 1.31 (s, 3H, CH3), 1.47 (s, 3H,
CH3), 4.33 (d, 1H, J = 3.3 Hz, C3-H), 4.57 (d, 1H, J = 3.3 Hz, C2-
H), 4.58 (s, 2H, OCH2Ph), 4.72 (br d, 1H, J = 3.3 Hz, C4-H), 5.84
(br s, 1H, CHN2), 6.01 (d, 1H, J = 3.3 Hz, C1-H), 7.25−7.37 (m, 5H,
Ar-H).
Colorless liquid; yield: 0.5 g, 66%; [α]D25 −64.59 (c 1, CHCl3).
IR (nujol): ν = 1740 (C=O) cm−1.
1H NMR (500 MHz, CDCl3): δ = 1.32 (s, 3H, CH3), 1.50 (s, 3H,
CH3), 2.80 (d, 2H, J = 7.0 Hz, CH2), 3.64 (s, 3H, OCH3), 4.01 (d,
1H, J = 3.0 Hz, C3-H), 4.46 (d, 1H, J = 12.0 Hz, OCH2Ph), 4.59 (dt,
1H, J = 7.0, 3.0 Hz C4-H), 4.62 (d, 1H, J = 3.5 Hz, C2-H), 4.65 (d,
1H, J = 12.0 Hz, OCH2Ph), 5.90 (d, 1H, J = 3.5 Hz, C1-H) 7.25−
7.37 (m, 5H, Ar-H).
Anal: C16H18N2O5 (318.32): Calc C, 60.37; H, 5.70. Found C,
60.34; H, 5.62.
1,2-O-Isopropylidene-3-O-benzyl-6-deoxy-6-diazo-a-D-ribo-
hexo-furan-5-ulose (5c)
White solid; yield: 0.86 g, 79%; mp 120−122 °C; [α]D25 +78 (c 1,
CHCl3).
Anal: C17H22O6 (322.35): Calc C, 63.34; H, 6.88. Found C, 63.17;
H, 6.85.
IR (nujol): ν = 2117 (CHN2), 1626 (C=O) cm−1.
5-Deoxy-3-O-benzyl-1,2-O-(1-methylethylidene)-α-D-ribo-
hexo-furanuronic Acid Methyl Ester (4c)
1H NMR (300 MHz, CHCl3): δ = 1.37 (s, 3H, CH3), 1.60 (s, 3H,
CH3), 3.84 (dd, 1H, J = 8.7, 3.9 Hz, C3-H), 4.50 (br d, 1H, J = 8.7,
C4-H), 4.56 (dd, 1H, J = 3.4, 3.9, C2-H), 4.70 (d, 1H, J = 12.3 Hz,
OCH2Ph), 4.80 (d, 1H, J = 12.3 Hz, OCH2Ph), 5.63 (br s, 1H,
CHN2), 5.79 (d, 1H, J = 3.4 Hz, C1-H), 7.25−7.45 (5H, m, Ar-H).
Colorless liquid; yield: 0.531 g, 70%; [α]D25 +92.44 (c 1, CHCl3).
IR (nujol): ν = 1741 (C=O) cm−1.
1H NMR (200 MHz, CDCl3): δ = 1.26 (s, 3H, CH3), 1.36 (s, 3H,
CH3), 2.46 (dd, 1H, J = 7.8, 15.1 Hz, CH2), 2.68 (dd, 1H, J = 3.9,
15.1 Hz, CH2), 3.66 (s, 3H, OCH3), 4.40 (ddd, 1H, J = 3.9, 7.8, 4.4
Hz, C4-H), 4.48−4.60 (m, 3H, C2-H, C3-H, OCH2Ph), 4.79 (d, 1H,
J = 11.7 Hz, OCH2Ph), 5.72 (d, 1H, J = 3.9 Hz, C1-H) 7.29−7.47
(m, 5H, Ar-H).
Anal: C16H18N2O5 (318.32): Calc C, 60.37; H, 5.70. Found C,
60.64; H, 5.88.
2,3-O-Isopropylidene-1-O-benzyl-6-deoxy-6-diazo-a-D-lyxo-
hexo-furano-5-ulose (5d)
To a soln of a-D-lyxo-furanuronic acid 6d (1 g, 3.4 mmol) in anhyd
THF (20 mL) at 0 °C was added Et3N (0.52 mL, 3.75 mmol) and
ethyl chloroformate (0.35 mL, 3.75 mmol) under N2 atm. The mix-
ture was stirred for 30 min and the solvent was removed under re-
duced pressure. The mixed anhydride thus obtained was directly
used in the next step. A solution of mixed anhydride in anhyd Et2O
was cooled to 0 °C under N2 atm and to this an ice-cooled solution
of diazomethane (0.57 g, 13.6 mmol) in Et2O (20 mL) was added
Anal: C17H22O6 (322.35): Calc C, 63.34; H, 6.88. Found C, 63.27;
H, 6.70.
5-Deoxy-1-O-benzyl-2,3-O-(1-methylethylidene)-α-D-lyxo-
hexo-furanosiduronic Acid Methyl Ester (4d)
Colorless liquid; yield: 0.516 g, 68%; [α]D25 +51.00 (c 1, MeOH).
IR (nujol): ν = 1741.1 (C=O) cm−1.
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J. N. Tilekar et al.
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1H NMR (200 MHz, CDCl3): δ = 1.32 (s, 3H, CH3), 1.46 (s, 3H,
CH3), 2.81 (d, 2H, J = 6.8 Hz, CH2), 3.74 (s, 3H, OCH3), 4.40−4.52
(m, 2H, OCH2Ph and C4-H), 4.66 (d, 1H, J = 5.8 Hz, C2-H), 4.71
(d, 1H, J = 11.7 Hz, OCH2Ph), 4.79 (dd, 1H, J = 5.8, 3.9 Hz C3-H),
5.07 (s, 1H, C1-H), 7.35 (br s, 5H, Ar-H).
(2) Wuts, P. G. M.; Bigelow, S. S. J. Org. Chem. 1988, 53, 5023.
Tatsuta, K.; Tanaka, A.; Fujimoto, K.; Kinoshita, M.;
Umezawa, S.; J. Am. Chem. Soc. 1977, 99, 5826.
Nakajima, N.; Uoto, K.; Matsushima, T.; Yonemitsu, O.;
Goto, H.; Osawa, E. J. Org. Chem. 1990, 55, 1129.
Keck, G. E.; Palani, A.; McHardy, S. F. J. Org. Chem. 1994,
59, 3113.
(3) Nicolaou, K. C.;. Pavia, M. R.; Seitz, S. P. Tetrahedron Lett.
1979, 25, 2327.
(4) Tronchet, J. M. J.; Baehler, B.; Bonenfant; A. Helv. Chim.
Acta 1976, 59, 941.
(5) For reviews on the reactions of diazocarbonyl compounds see:
Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091.
Miller, D. J.; Moody, C. J. Tetrahedron 1995, 51, 10811.
Padwa, A.; Weingarten, M. D. Chem. Rev. 1996, 96, 223.
Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911.
(6) Bachmann, W. E.; Stuve, W. S. Org. React. (N. Y.) 1942, 1,
38.
Anal: C17H22O6 (322.35): Calc C, 63.34; H, 6.88. Found C,63.45; H,
6.95.
2(E) Octenedioic acid, 4(R), 6(S)-dihyroxy-5(R)-methoxy-1-eth-
yl- 8-methyl Ester (3)
An ice-cooled solution of TFA/H2O (2:1, 2 mL) was added to 5-
deoxy-3-O-methyl-1,2-O-(1-methylethylidene)-α-D-xylo-hexo-
furanuronic acid methyl ester (4a, 0.5 g, 2.03 mmol) at 0 °C. The
solution was allowed to attain r.t. and stirred for 1.5 h. The acid was
removed under reduced pressure and the residue obtained was puri-
fied by chromatography on silica gel (CHCl3/MeOH, 19:1) to give
methyl 5-deoxy-3-O-methyl-α-D-xylo-hexo-1,4-furanuronate as a
1
viscous liquid; yield: 0.37 g, 90%. (The H NMR spectra showed
Ando, W. In Chemistry of Diazonium and Diazo Groups;
Patai, S., Ed.; Wiley: New York, 1978; pp 458−475 and
references therein.
the presence of methyl ester signal and the absence of 1,2-O-isopro-
pylidene functionality). To a solution of methyl 5-deoxy-3-O-meth-
yl-α-D-xylo-hexo-1,4-furanuronate (0.37 g, 1.79 mmol) in anhyd
toluene (10 mL) was added triphenylethoxycarbonylmethylene
phosphorane (0.75 g, 2.15 mmol). The mixture was stirred at r.t. for
16 h. The solvent was evaporated at reduced pressure to give a thick
liquid which on column chromatography on silica gel (CHCl3/
MeOH, 98:2) gave 3 as a crystalline solid. Yield: 0.39 g, 80%; mp
(7) Wang, J.; Hou, Y. J. Chem. Soc., Perkin Trans. 1 1998, 1919
and references therein.
(8) Charon, D. Carbohydr. Res. 1969, 11, 447.
(9) Dhavale, D. D.; Bhujbal, N. N.; Joshi, P.; Desai, S. G.
Carbohydr. Res. 1994, 263, 303.
48−49 °C, [Lit3 mp 48−49 °C]; [α]D −8.50 (c 1, MeOH), [Lit3
25
Dhavale, D. D.; Desai,V. N.; Sindkhedkar, M. D.; Mali, R. S.;
Castellari, C.; Trombini, C. Tetrahedron Asymmetry, 1997, 8,
1475.
Dhavale, D. D.; Saha, N. N.; Desai, V. N. J. Org. Chem. 1997,
62, 7482.
25
[α]D -8.74 (c 1, MeOH)]. The spectral and analytical data is in
agreement with the reported data.3
Acknowledgement
Saha, N. N.; Desai, V. N.; Dhavale, D. D. J. Org. Chem. 1999,
64, 1715.
Desai, V. N.; Saha, N. N.; Dhavale, D. D. J. Chem. Soc.,
Chem. Comm. 1999, 1719.
We are thankful to IIT and TIFR Bombay for high resolution NMR
facility and to Prof. M. S. Wadia for helpful discussions. Financial
support from the DRDO (project no. RDR-PX-34/ERD-1004.03) is
gratefully acknowledged.
(10) Dhavale, D. D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi,
A. J. Org. Chem., 1989, 54, 4100.
Dhavale, D. D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi,
A. Tetrahedron Lett. 1988, 47, 6163.
Ireland, R. E.; Norbeck, D. W. J. Am. Chem. Soc. 1985, 107,
3279.
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