First efficient synthesis of (±)-erythro-roccellic acid

Article abstract of DOI:10.1039/b104105n

An easy, four-step route to (±)-erythro-2-dodecyl-3-methylbutanedioic acid (roccellic acid, 9) with 60% overall yield has been described. Wittig reaction of the citraconimide-TPP adduct with dodecanal furnished the mixture of (E)- and (Z)-isomers 3 and 4,

Full text of DOI:10.1039/b104105n

View Article Online / Journal Homepage / Table of Contents for this issue
First efficient synthesis of ( )-erythro-roccellic acid†
Sivaprakasam Mangaleswaran and Narshinha P. Argade*
Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411 008,
India. E-mail: argade@dalton.ncl.res.in; Fax: ϩ 91-20-5893153
1
Received (in Cambridge, UK) 4th May 2001, Accepted 19th June 2001
First published as an Advance Article on the web 9th July 2001
An easy, four-step route to ( )-erythro-2-dodecyl-3-methylbutanedioic acid (roccellic acid, 9) with 60% overall
yield has been described. Wittig reaction of the citraconimide–TPP adduct with dodecanal furnished the mixture of
(E)- and (Z)-isomers 3 and 4, which, on base-catalysed exocyclic to endocyclic double bond isomerisation, yielded
maleimide 5. Catalytic cis-hydrogenation of 5 using Adam’s platinum dioxide catalyst followed by acid-catalysed
hydrolysis of formed succinimide 8 gave desired ( )-erythro-roccellic acid 9.
Introduction
(ϩ)-Roccellic acid [(2R,3S)-2-dodecyl-3-methylbutanedioic
acid, 1] occurs in lichens1,2 and it was first isolated in 1898. In
the past century it has been isolated from the following lichen
species: Roccella capensis,3 R. fuciformis,4,5 R. hypomecha,6
R. gayana,7 R. fucoides,7,8 R. condensata,9 R. montagnei,10,11
Dirinaria aegialita,12 D. applanata,12 D. confusa saxicola,12 D.
consimilis,12 D. leopoldii,12 Pyxine berteriana,12 P. caesiopru-
inosa,12 P. pungens,12 Lobodirina cerebriformes,13 L. mahuiana,14
Acarospora chlorophana,15 Lecanora riparia,16 L. rupicola,17,18
L. sordida,19,20 Lepraria latebrarum,21 L. aeruginosa,22 Dirina
lutosa,23 Crocynea membranacea24,25 and more recently from
Haematomma nemetzii26 and Tornabena scutellifera26 with
a major contribution from Siegfried Huneck’s group. The
structural assignment of roccellic acid 1 has been made on
the basis of analytical and spectral data.17,19,24,26 Its absolute
configuration was established by Åkermark by degrading 1 to
its two isomeric monomethyl esters.24,27 Roccellic acid 1
possesses antituberculosis activity28–30 and concentration-
dependent plant growth promoter31–33/inhibitor33,34 activity. It
is also used for (i) the synthesis of structural analogues of the
antibiotic actinonin,35 (ii) the precipitation of human serum
albumin36 and (iii) the preparation of coloured metal
complexes.37 To date, two syntheses38,39 of unnatural ( )-threo-
roccellic acid (major) are known starting from diethyl malonate
and during these studies a small amount (25 mg) of ( )-erythro-
roccellic acid has been obtained by an 8-step synthesis with
0.026% overall yield.38 The provision of facile synthetic
approaches to this bioactive natural product roccellic acid is
a challenging task of current interest. Recently we have
reported40 the first coupling reaction of the citraconimide 2 and
triphenylphosphine (TPP) adduct41 with aliphatic aldehydes
and used it for the synthesis of the recently isolated bioactive
natural products chaetomellic acid A,40 ( )-piliformic acid,42
and tyromycin A.43 We herein report yet another useful applic-
ation of this coupling reaction to complete the first efficient
synthesis of ( )-erythro-roccellic acid 9 by the cis-reduction of
Scheme 1 Reagents, conditions and yields: (i) TPP, AcOH, dodecanal,
reflux, 10 h (82%); (ii) TEA, THF, reflux, 48 h (98%); (iii) (a) KOH,
THF, MeOH, H2O, reflux, 2 h; (b) Hϩ/HCl (98%); (iv) Adam’s catalyst,
petroleum spirit, H2, rt, 10 h (9: 60%; 8: 95%); (v) CF3COOH, conc.
HCl, reflux, 48 h (98%); (vi) CH2N2, Et2O, rt, 2 h, (98%).
maleimide 5 to succinimide 8 employing a catalytic hydrogen-
ation reaction with Adam’s catalyst (Scheme 1).
Results and discussion
A mixture of equimolar amounts of citraconimide 2 and TPP
on refluxing with 1.5 equivalents of dodecanal in glacial acetic
acid for 10 h yielded a combination of geometric isomers 3 and
† NCL Communication No. 6609.
1764
J. Chem. Soc., Perkin Trans. 1, 2001, 1764–1766
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b104105n

View Article Online
4 in 82% yield by a Wittig reaction. The integration values for
the vinylic protons in the H NMR spectra of this mixture of
phine and dodecanal were obtained from Aldrich Chemical
Co. Petroleum spirit refers to the fraction with distillation range
1
geometric isomers (E)-3 and (Z)-4 revealed that they are
formed in an 85 : 15 ratio. The mixture of exo-isomers 3 and 4
on refluxing with triethylamine–THF (1 : 1) for 48 h, underwent
a smooth exocyclic to endocyclic carbon–carbon double bond
isomerisation to yield dodecylmethylmaleimide 5 in 98% yield.
On alkaline hydrolysis followed by acidification, the maleimide
5 gave the desired dodecylmethylmaleic anhydride 6 in 98%
yield. We systematically studied the catalytic cis-hydrogenation
reactions of maleimide 5 and disubstituted maleic anhydride 6
to obtain succinimide derivative 8 and succinic anhydride
derivative 7 respectively. In our hands, the anhydride 6 and
imide 5, when subjected to catalytic hydrogenation with
palladium on charcoal as catalyst in methanol, remained com-
pletely unreacted for 12 h at 50 psi pressure of hydrogen. The
anhydride 6 in petroleum spirit on treatment with Adam’s
platinum dioxide catalyst at 50 psi pressure of hydrogen for 10 h
followed by filtration, concentration and recrystallisation with
acetone gave the desired ( )-erythro-roccellic acid 9 in 60%
yield. We were unable to isolate the intermediate anhydride 7
under the present set of reaction conditions. The maleimide
5 underwent a very smooth catalytic cis-hydrogenation at rt in
petroleum spirit with Adam’s platinum dioxide catalyst at 50
psi hydrogen pressure in 10 h to yield the desired cis-
succinimide derivative 8 in 95% yield. The reaction of male-
imide 5 to succinimide 8 was much cleaner and more efficient
compared to the conversion of 6 to 9 via 7. The cis-succinimide
derivative 8 on hydrolysis using refluxing mixture of acetic acid
plus conc. hydrochloric acid (1 : 1) gave a mixture of erythro-
and threo-isomers of roccellic acid, in a 2 : 1 ratio (by 1H NMR,
from the integration values of the methine protons) in 48 h with
98% yield. The cis-succinimide derivative 8 on hydrolysis in
refluxing mixture of trifluoroacetic acid and conc. hydrochloric
acid (1 : 1) gave a mixture of the desired erythro- and undesired
threo-isomers with a much better proportion of the erythro-
60–80 ЊC.
( )-(E/Z)-2-Dodecylidene-3-methyl-N-(p-tolyl)succinimides 3
and 4
A mixture of citraconimide 2 (3.01 g, 15 mmol), TPP (3.93 g,
15 mmol) and dodecanal (4.14 g, 22.5 mmol) in glacial acetic
acid (50 mL) was refluxed with stirring for 10 h. Acetic acid was
distilled off in vacuo at 50 ЊC and the residue was dissolved
in ethyl acetate (60 mL). The organic layer was washed succes-
sively with water (30 mL), brine (20 mL) and dried over
Na2SO4. Concentration of the organic layer in vacuo followed
by silica gel column purification of the residue using petroleum
spirit–ethyl acetate (9 : 1) gave a mixture of 3 and 4 (3 : 4 =
1
85 : 15 by H NMR) (4.54 g, 82%); mp 49–52 ЊC; IR (Nujol)
νmax 1717, 1458 cmϪ1; 1H NMR δH 0.88 (t, J 6 Hz, 3 H), 1.27 (br
s, 16 H), 1.45–1.60 (m, 2 H), 1.48 (d, J 6 Hz, 0.45 H, Z-isomer),
1.52 (d, J 6 Hz, 2.55 H), 2.20–2.36 (m, 1.7 H), 2.38 (s, 3 H),
2.74–2.92 (m, 0.3 H, Z-isomer), 3.34–3.59 (m, 1 H), 6.23 (dt, J 8
and 3 Hz, 0.15 H, Z-isomer), 6.92 (dt, J 8 and 3 Hz, 0.85 H),
7.20 (d, J 8 Hz, 2 H), 7.28 (d, J 8 Hz, 2 H); MS m/z 369 (Mϩ,
85%), 354 (4), 340 (4), 270 (5), 256 (8), 242 (100), 229 (28), 216
(47), 203 (80), 186 (8), 170 (4), 157 (4), 144 (4), 132 (12), 118
(18), 107 (46), 95 (62), 91 (29), 81 (55), 68 (82), 55 (9) (Calc. for
C24H35NO2: C, 78.00; H, 9.55; N, 3.80. Found: C, 78.16; H,
9.39; N, 3.92%).
2-Dodecyl-3-methyl-N-(p-tolyl)maleimide 5
A solution of the mixture of 3 and 4 (3.3 g) in THF (15 mL)
and triethylamine (15 mL) was refluxed for 48 h with stirring.
The reaction mixture was then allowed to reach rt, and was
concentrated in vacuo; silica gel column chromatographic
purification of the residue using petroleum spirit–ethyl acetate
(9 : 1) gave pure 5 (3.23 g, 98%), mp 68–69 ЊC; IR (Nujol) νmax
1710, 1690, 1650 cmϪ1; 1H NMR δH 0.89 (t, J 8 Hz, 3 H), 1.27
(br s, 18 H), 1.50–1.75 (m, 2 H), 2.05 (s, 3 H), 2.38 (s, 3 H), 2.46
(t, J 8 Hz, 2 H), 7.10–7.40 (m, 4 H); 13C NMR (CDCl3, 50
MHz) δC 8.7, 14.0, 21.0, 22.6, 23.8, 28.1, 29.3, 29.6 (6 × CH2),
31.9, 125.6, 129.5, 137.1, 137.2, 141.4, 159.7, 170.7, 171.1; MS
m/z 369 (Mϩ, 85%), 256 (6), 228 (10), 215 (100), 203 (8), 107
(48), 91 (29), 81 (41), 67 (20), 55 (10) (Calc. for C24H35NO2: C,
78.00; H, 9.55; N, 3.80. Found: C, 77.72; H, 9.78; N, 3.71%).
1
isomer (93 : 7, by H NMR, from the integration values of the
methine protons) in 48 h with 98% yield. Recrystallisation of
the above mixture of erythro- and threo-isomers (93 : 7) from
acetone gave the desired ( )-erythro-roccellic acid 9 in 80%
yield. The formed acid 9 was further characterised as its di-
methyl ester 10. The analytical and spectral data obtained for
( )-erythro-roccellic acid 9 and its corresponding dimethyl ester
10 were in complete agreement with reported data.2,17,38 The
asymmetric catalytic hydrogenation44–46 of maleimide 5 will
provide an elegant route to the desired naturally occurring
bioactive (ϩ)-(2R,3S)-roccellic acid 1.
In summary, we have demonstrated the first efficient four-
step synthesis of ( )-erythro-roccellic acid 9 with 60% overall
yield, starting from citraconimide 2 by a catalytic cis-
hydrogenation pathway and the present strategy will be useful
for obtaining several 2,3-dialkyl substituted succinic acid
derivatives.
2-Dodecyl-3-methylmaleic anhydride 6
To the solution of imide 5 (1.11 g, 3 mmol) in a THF–methanol
mixture (1 : 2, 18 mL) was added 30% aqueous KOH solution
(10 mL) and the reaction mixture was refluxed for 2 h with
stirring. The reaction mixture was concentrated in vacuo and
the residue was acidified with dilute HCl, extracted with diethyl
ether (3 × 50 mL) and the organic layer was washed with water
(20 mL), brine (20 mL) and dried over Na2SO4. Concentration
of the organic layer in vacuo followed by silica gel column
chromatographic purification of the residue using petroleum
spirit–ethyl acetate (9 : 1) furnished pure 6 as a thick oil (0.82 g,
Experimental
Melting points were taken on a Büchi melting point B-540
apparatus and are uncorrected. The 1H NMR spectra were
recorded in CDCl3 with TMS as an internal standard on a
Bruker AC 200 NMR spectrometer (200 MHz) and for roccellic
acid 9 in pyridine-d5 with TMS as an internal standard on a
Bruker DRX 500 NMR spectrometer (500 MHz). The 13C
NMR spectra were recorded on Bruker AC 200 (50 MHz),
Bruker MSL 300 (75 MHz) and Bruker DRX 500 NMR
spectrometers (125 MHz). Mass spectra were recorded on a
Finnigan Mat 1020 ЊC mass spectrometer at 70 eV. The FT-IR
spectra were recorded on an FT-IR-8300 Shimadzu spec-
trometer and microanalyses were carried out on a Carlo-Erba
instrument; column chromatographic separation was per-
formed with ACME silica gel (60–120 mesh). Triphenylphos-
98%); IR (Nujol) νmax 1823, 1767, 1674, 1466 cmϪ1; H NMR
1
δH 0.88 (t, J 6 Hz, 3 H), 1.26 (br s, 18 H), 1.45–1.70 (m, 2 H),
2.07 (s, 3 H), 2.46 (t, J 6 Hz, 2 H); 13C NMR (CDCl3, 50 MHz)
δC 9.2, 13.9, 22.5, 24.3, 27.4, 29.3, 29.5 (6 × CH2), 31.8, 140.3,
144.6, 165.7, 166.1; MS m/z 281 (MHϩ, 10%), 262 (18), 252
(12), 235 (13), 207 (20), 196 (14), 178 (42), 168 (29), 150 (15),
139 (10), 126 (95), 109 (12), 98 (26), 81 (33), 67 (30) (Calc. for
C17H28O3: C, 72.82; H, 10.06. Found: C, 73.05; H, 9.93%).
( )-erythro-2-Dodecyl-3-methyl-N-(p-tolyl)succinimide 8
A mixture of maleimide 5 (1.1 g, 3 mmol) and Adam’s catalyst
(25 mg) in petroleum spirit (50 mL) was subjected to hydrogen-
ation at 50 psi hydrogen pressure for 10 h at rt. The reaction
J. Chem. Soc., Perkin Trans. 1, 2001, 1764–1766
1765

View Article Online
2 S. Huneck, J. Schmidt and A. Porzel, Z. Naturforsch., B: Chem. Sci.,
1994, 49, 561.
3 S. Huneck, J. Jakupovic and G. Follmann, Z. Naturforsch., B: Chem.
Sci., 1991, 46, 969.
4 S. Huneck, Phytochemistry, 1972, 11, 1489.
5 S. Huneck, A. Mathey and G. Trotet, Z. Naturforsch., B: Anorg.
Chem. Org. Chem., 1967, 22, 1367.
6 S. Huneck and G. Follmann, Ber. Dtsch. Bot. Ges., 1968, 81, 125
(Chem. Abstr., 1969, 70, 35025j).
7 S. Huneck and G. Follmann, Z. Naturforsch., B: Anorg. Chem. Org.
Chem., 1967, 22, 1369.
8 S. Huneck, G. Follmann, A. W. William and G. Trotet, Z.
Naturforsch., B: Anorg. Chem. Org. Chem., 1967, 22, 671.
9 S. Huneck and G. Follmann, Z. Naturforsch., B: Anorg. Chem. Org.
Chem., 1967, 22, 1185.
10 V. Subba Rao and T. R. Seshadri, Proc. Indian Acad. Sci., Sect. A,
1940, 12, 466.
11 V. Subba Rao and T. R. Seshadri, Proc. Indian Acad. Sci., Sect. A,
1941, 13, 199.
12 S. Huneck, M. A. Morales and K. Kalb, J. Hattori Bot. Lab., 1987,
62, 331 (Chem. Abstr., 1988, 108, 19191h).
13 W. Quilhot, J. A. Garbarino and V. Gambaro, J. Nat. Prod., 1983,
46, 593.
14 W. Quilhot, J. Redon, E. Zuniga and S. Vidal, Phytochemistry, 1975,
14, 1865.
15 S. Huneck, Lichenologist, 1980, 12, 239.
16 S. Huneck, Phytochemistry, 1972, 11, 1493.
17 J. P. Devlin, C. P. Falshaw, W. D. Ollis and R. E. Wheeler, J. Chem.
Soc. (C), 1971, 1318.
18 C. H. Fox and S. Huneck, Phytochemistry, 1969, 8, 130.
19 G. Kennedy, J. Breen, J. Keane and T. J. Nolan, Sci. Proc. R. Dublin
Soc., 1937, 21, 557.
20 O. Hesse, J. Prakt. Chem., 1898, 58, 497.
21 K. Soviar, Acta Fac. Pharm. Univ. Comenianae, 1971, 20, 27 (Chem.
Abstr., 1972, 76, 123969z).
22 K. Soviar, M. Bachrata, D. Georch and L. Krasnec, Farm. Obz.,
1967, 36, 161 (Chem. Abstr., 1969, 70, 44812r).
23 S. Huneck and G. Follmann, Z. Naturforsch., B: Anorg. Chem. Org.
Chem., 1964, 19, 658.
24 B. Åkermark, Acta Chem. Scand., 1962, 16, 599.
25 B. Åkermark, H. Erdtman and C. A. Wachtmeister, Acta Chem.
Scand., 1959, 13, 1855.
mixture was filtered through Celite and the filtrate was concen-
trated in vacuo. The silica gel column purification of the residue
using petroleum spirit–ethyl acetate (9 : 1) gave succinimide 8
(1.05 g, 95%), mp 67–68 ЊC (from methanol); IR (Nujol) νmax
1774, 1709, 1516, 1470 cmϪ1 1H NMR (CDCl3, 200 MHz)
;
δH 0.91 (t, J 6 Hz, 3 H), 1.29 (br s, 20 H), 1.35 (d, J 6 Hz, 3 H),
1.60–1.95 (m, 2 H), 2.39 (s, 3 H), 2.85–3.20 (m, 2 H), 7.16 (d, J 8
Hz, 2 H), 7.28 (d, J 8 Hz, 2 H); 13C NMR (CDCl3, 50 MHz)
δC 11.6, 13.9, 21.0, 22.6, 26.5, 27.6, 29.3, 29.5 (6 × CH2), 31.8,
38.6, 43.8, 126.1, 129.6, 138.2, 138.4, 178.4, 179.3; MS m/z 371
(Mϩ, 24%), 265 (4), 216 (29), 203 (80), 175 (7), 134 (12), 107
(20), 91 (12), 69 (18) (Calc. for C24H37NO2: C, 77.58; H, 10.03;
N, 3.77. Found: C, 77.76; H, 10.14; N, 3.53%). Similarly, on
catalytic hydrogenation, anhydride 6 (0.56 g, 2 mmol) furnished
( )-erythro-roccellic acid 9 (0.36 g, 60%).
( )-erythro-Roccellic acid 9
Succinimide 8 (0.74 g, 2 mmol) was dissolved in trifluoroacetic
acid–conc. hydrochloric acid (1 : 1, 15 mL) and the reaction
mixture was refluxed for 48 h. The reaction mixture was kept
aside at rt for 12 h and the white precipitate of roccellic acid was
filtered in vacuo to obtain 9 (0.59 g, 98%) (erythro : threo =
93 : 7, proved by 1H NMR). The mixture of erythro- and threo-
roccellic acid (0.50 g, 93 : 7) was recrystallised from acetone
(30 mL) to obtain pure ( )-erythro-roccellic acid 9 (0.40 g,
80%), mp 141–142 ЊC (from acetone); IR (Nujol) νmax 1693,
1
1464, 1271, 1202 cmϪ1; H NMR (pyridine-d5, 500 MHz) δH
0.86 (t, J 5 Hz, 3 H), 1.20 (br s, 16 H), 1.30–1.45 (m, 2 H), 1.62
(d, J 10 Hz, 3 H), 1.53–1.75 (m, 2 H), 1.92–2.03 (m, 1 H), 2.10–
2.23 (m, 1 H), 3.17–3.33 (m, 2 H); 13C NMR (pyridine-d5, 125
MHz) δC 14.2, 16.2, 22.8, 28.2, 29.5, 29.8 (6 × CH2), 31.7, 32.0,
43.4, 50.0, 177.0, 177.7; MS m/z 282 (Mϩ, 1%), 254 (2), 227 (7),
209 (3), 170 (10), 156 (17), 132 (35), 97 (33), 83 (28), 69 (54)
(Calc. for C17H32O4: C, 67.96; H, 10.73. Found: C, 67.85; H,
10.65%).
26 S. Huneck, U. Himmelreich, J. Schmidt, J. Volker and U. Zeybek,
Z. Naturforsch., B: Chem. Sci.,, 1994, 49, 1561.
27 B. Åkermark, Acta Chem. Scand., 1970, 24, 1456.
28 V. C. Barry and P. A. McNally, Nature, 1945, 156, 48.
29 V. C. Barry, J. G. Belton, R. M. Kelly and D. Twomey, Nature, 1950,
166, 303.
30 F. M. Pereira, J. de sa and S. S. Bhatnagar, Indian J. Pharm., 1953,
15, 287.
31 C. F. Garcia, G. A. Espinoza, S. G. Coltantes, V. V. Rios and P. W.
Quilhot, J. Hattori Bot. Lab., 1982, 53, 443 (Chem. Abstr., 1982, 97,
212854j).
32 P. W. Quilhot, V. J. Thompson, B. S. Vidal and P. G. Campos,
J. Hattori Bot. Lab., 1981, 49, 273 (Chem. Abstr., 1981, 95, 1773c).
33 S. Huneck and K. Schreiber, Phytochemistry, 1972, 11, 2429.
34 K. Schreiber, Environ. Qual. Saf. Suppl., 1975, 3, 483 (Chem. Abstr.,
1976, 85, 105260t).
35 J. P. Devlin, W. D. Ollis and J. E. Thorpe, J. Chem. Soc., Perkin
Trans. 1, 1975, 846.
36 W. McD. Armstrong, Proc. R. Ir. Acad., Sect. B, 1956, 58, 71.
37 I. K. Iskandar and J. K. Syers, J. Soil Sci., 1972, 23, 255.
38 B. Åkermark and N. G. Johansson, Ark. Kemi, 1967, 27, 1.
39 V. C. Barry and D. Twomey, Proc. R. Ir. Acad., Sect. B, 1947, 51,
137.
Dimethyl ester of ( )-erythro-roccellic acid 10
A solution of ( )-erythro-roccellic acid 9 (0.30 g, 1 mmol) in
ether (10 mL) was treated with a solution of diazomethane in
ether at 0 ЊC, until the complete consumption of the starting
material (2 h). The excess of diazomethane was quenched with
acetic acid and the reaction mixture was concentrated in vacuo.
Silica gel column chromatographic purification of the residue
using petroleum spirit and ethyl acetate mixture (9 : 1) gave
pure 10 as a thick oil (0.32 g, 98%); IR (neat) νmax 1740, 1464,
1
1435, 1195 cmϪ1; H NMR (CDCl3, 200 MHz) δH 0.87 (t, J 6
Hz, 3 H), 1.13 (d, J 6 Hz, 3 H), 1.23 (br s, 18 H), 1.30–1.50 (m,
2 H), 1.50–1.75 (m, 2 H), 2.58–2.78 (m, 2 H), 3.68 (s, 3 H), 3.69
(s, 3 H); 13C NMR (CDCl3, 75 MHz) δC 14.0, 15.1, 22.7, 27.5,
29.4, 29.6 (6 × CH2), 30.7, 31.9, 42.1, 48.6, 51.4, 51.7, 174.6,
175.3; MS m/z 328 (Mϩ, 1%), 298 (24), 267 (7), 242 (100), 184
(16), 170 (18), 160 (88), 128 (66), 111 (17), 101 (32), 91 (68), 81
(29), 69 (68), 55 (92) (Calc. for C19H36O4: C, 69.47; H, 11.04.
Found: C, 69.54; H, 11.23%).
40 S. B. Desai and N. P. Argade, J. Org. Chem., 1997, 62, 4862.
41 E. Hedaya and S. Theodoropulos, Tetrahedron, 1968, 24, 2241.
42 S. Mangaleswaran and N. P. Argade, J. Chem. Soc., Perkin Trans. 1,
2000, 3290.
43 S. Mangaleswaran and N. P. Argade, J. Org. Chem., 2001, 66, 5259.
44 H. Muramatsu, H. Kawano, Y. Ishii, M. Saburi and Y. Uchida,
J. Chem. Soc., Chem. Commun., 1989, 769.
Acknowledgements
S. M. thanks C.S.I.R., New Delhi, for the award of a fellowship.
We thank Dr K. N. Ganesh, Head of the Division of Organic
Chemistry (Synthesis), for constant encouragement.
45 M. Kitamura, M. Tokunaga and R. Noyori, J. Org. Chem., 1992, 57,
4053.
References
46 M. V. Berg, A. J. Minnaard, E. P. Schudde, J. V. Esch, A. H. M. Vries,
J. G. Varies and B. L. Feringa, J. Am. Chem. Soc., 2000, 122, 11539.
1 The Merck Index, 12th Edition, 1996, p. 1419.
1766
J. Chem. Soc., Perkin Trans. 1, 2001, 1764–1766