Convenient synthesis of dithiooxamides from N-arylimino-1,2,3- dithiazoles

Article abstract of DOI:10.1055/s-1999-3555

Among several useful transformations of the readily available N- arylimino-1,2,3-dithiazoles 1 is their rapid conversion by lithium aluminum hydride into the rearranged N-aryldithiooxamides, ArNHCSCSNH₂, thus providing a two step synthesis of t

Full text of DOI:10.1055/s-1999-3555

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Thierry Besson,a Charles W. Rees,b Valérie Thiérya
a Laboratoire de Génie Protéique et Cellulaire, UPRES 2001, Groupe de Chimie Organique, Pôle Sciences et Technologie,
Université de La Rochelle, Avenue Marillac, F-17042 La Rochelle cedex 1, France
Fax +33(5)46458247; E-mail: vthiery@cri.univ-lr.fr; E-mail: tbesson@cri.univ-lr.fr
b Department of Chemistry, Imperial College of Science, Technology and Medicine, London, SW7 2AY, UK
Fax +44(171)5945800
5HFHLYHGꢀꢁꢀ)HEUXDU\ꢀꢂꢃꢃꢃꢄꢀUHYLVHGꢀꢁꢂꢀ0DUFKꢀꢂꢃꢃꢃ
aluminum hydride (LAH) and observed an entirely differ-
$EVWUDFWꢈꢄ Among several useful transformations of the readily
ent, unexpected, reaction which resulted in the formation
available 1-arylimino-1,2,3-dithiazoles ꢀ is their rapid conversion
of 1-aryldithiooxamides ꢃ. The reaction of iminodithiaz-
oles ꢀ in anhydrous THF under argon with LAH (1 molar
by lithium aluminum hydride into the rearranged 1-aryldithiooxa-
mides, ArNHCSCSNH2, thus providing a two step synthesis of
these unsymmetrical rubeanic acid derivatives from ArNH2 (9 ex- equiv) was rapid and exothermic to give the red or orange
amples).
crystalline 1-aryldithiooxamides ꢃ shown in the Table.
Although the yields are only modest, the reaction provides
an easy, general, two-step conversion of ArNH2
.H\ꢄ ZRUGVꢈ 1-arylimino-1,2,3-dithiazoles, aryl isothiocyanates,
cyanothioformamides, dithiooxamides, rubeanic acid
Æ
ArNHCSCSNH2. Sodium borohydride, sodium cy-
anoborohydride or sodium bis(2-methoxyethoxy)alumi-
num hydride (Red-Al) were less effective since they gave
much less dithiooxamides ꢃ but afforded cyanothioforma-
nilides ꢁ as the major product. Less than one molar equiv-
alent of LAH resulted in lower yields of ꢃ. Yields were
mostly in the 35–42% range, except where there was an R-
chloro substituent (ꢃG) or a SHUL ring nitrogen (ꢃK).
Primary aromatic amines are readily converted into the
stable arylimino-1,2,3-dithiazoles (ꢀꢉ in high yield.1
These derivatives are versatile synthetic intermediates,
undergoing a variety of reactions initiated by nucleophilic
attack at different sites on the dithiazole ring.2 Some of
these reactions transform the dithiazole ring only, whilst
others involve cyclisation onto the adjacent aromatic ring.
The former are shown in Scheme 1.
Conversion of -Aryliminodithiazoles into
Aryldithiooxamides
-
Product
Ar
Appearance
Yield
(%)
Ph
red needles
34
45
35
25
43
40
37
4-MeOC6H4
3,4,5-(MeO)3C6H2
2-CIC6H4
red needles
orange needles
red needles
Thermolysis of the imines ꢀ gave cyanoimidoyl chlorides
ꢇ and disulfur, particularly when the RUWKR-positions of
the aryl ring are substituted or when this ring has electron-
withdrawing substituents.3 Reduction of the imines ꢀ with
one equivalent of sodium hydride4 or of their hydrochlo-
ride salts with sodium cyanoborohydride5 gave the cyan-
othioformanilides ꢁ which react further with sodium
hydride, with elimination of cyanide, to give aryl isothio-
cyanates ꢂ.4 Imines ꢀ were directly converted into ꢂ by
treatment with two equivalents of sodium hydride in boil-
ing THF overnight.4 In an attempt to achieve this last re-
action more quickly, we treated the imines with lithium
3,4-F2C6H3
2-HOCH2CH2C6H4
orange needles
orange needles
red needles
8-quinolinyl
3-quinolinyl
orange needles
orange needles
16
40
Synthesis 1999, No. 8, 1345–1348 ISSN 0039-7881 © Thieme Stuttgart · New York

ꢀꢁꢂꢊ
T. Besson et al.
3$3(5
IR spectra were recorded on a Perkin-Elmer paragon 1000PC in-
strument. 1H and 13C NMR spectra were recorded on a JEOL JNM
LA (400MHz) spectrometer (Laboratoire Commun d’Analyse, Uni-
versité de la Rochelle, France) ; chemical shifts (d) are reported in
parts per million (ppm) downfield from TMS, which was used as in-
ternal standard. UV spectra were recorded on a Perkin-Elmer
Lambda 16 UV/Vis. spectrometer. Mass spectra were recorded on a
Varian MAT311 in the Centre Régional de Mesures Physiques de
l’Ouest (C.R.M.P.O.), Université de Rennes, France. Chromatogra-
phy was carried out on silica gel 60 at medium pressure with the
mixtures preadsorbed onto silica. TLC was performed on Merck
Kieselgel 60 F254 aluminium backed plates. Light petroleum ether
refers to the fraction bp 40–60°C.
The highly coloured products ꢃ are derivatives of rubeanic
acid (dithiooxamide)6 which has a long history as a chelat-
ing ligand, an analytical reagent, particularly for copper,
cobalt and nickel,7 and as a stabilizer of ascorbic acid so-
lutions.
This conversion of arylimino-1,2,3-dithiazoles ꢀ into
dithiooxamides ꢃ is unusual since, i) it is the first reaction
of ꢀ in which all the C, N, and S atoms have been retained
in the product (see Scheme 1) with no loss of sulfur in
spite of the strongly reducing conditions, and ii) the con-
nectivity of the heterocyclic ring atoms has changed, with
the original S-2 atom becoming bound to carbon, indicat-
ing a molecular rearrangement or an elimination-addition
pathway.
1ꢅꢌꢂꢅ&KORURꢅꢃ+ꢅꢀꢆꢇꢆꢁꢅGLWKLD]ROꢅꢃꢅ\OLGHQHꢉDQLOLQHVꢄꢀ
These were prepared from 4,5-dichloro-1,2,3-dithiazolium chloride
and the primary amines as previously described.1–4
Whilst we have no firm evidence for a particular mecha-
nism, it seems likely2–4 that the reduction starts by attack
at S-2 with opening of the heterocyclic ring to give the cy-
ano intermediate ꢊ (Scheme 2). The disulfide bond of ꢊ
would presumably be readily reduced to give the cyan-
othioformanilide ꢁ and its anion, together with hydrogen
sulfide and HS–. This last would then be expected to add
to the cyano group of ꢁ to give the observed thioamide ꢃ
(Scheme 2). The well known base-catalysed addition of
hydrogen sulfide to cyanides8 has already been demon-
strated for cyanothioformamides.9, 10
$U\Oꢄ'LWKLRR[DPLGHVꢄꢃD±Lꢈꢄ*HQHUDOꢄ3URFHGXUHꢄ
Under an argon atmosphere, a solution of 1-aryliminodithiazoles ꢀ
(0.7 mmol) in anhyd THF (5 mL) was treated with LiAIH4 (27 mg,
0.7 mmol) and stirred for 15 min at r.t. The reaction mixture was di-
luted with EtOAc (7 mL) and washed with satd aq NaHCO3 solu-
tion. The organic layer was dried (Na2SO4) and the solvent
evaporated. The residue was column-chromatographed on silica gel
using CH2Cl2/EtOAc as eluent, and the products were crystallised
from light petroleum/CH2Cl2.
1ꢅ3KHQ\OGLWKLRR[DPLGHꢄꢌꢃDꢉꢄ
Red needles (34%), mp 101–102°C (light petroleum/CH2Cl2) (Lit.9a
mp 99°C).
UV (EtOH): lmax (log e) = 232(4.16), 323 (4.04), 375 nm (3.66)
IR (KBr): n = 3292, 3135, 1589, 1539, 1490, 1443, 1237, 1102,
1020 cm-1.
1H NMR (400 MHz, CDCl3): d = 7.32 (t, 2 H, - = 7.45 Hz, Harom),
7.46 (t, 2 H, - = 7.55 Hz, Harom), 7.85 (br s, 1 H, NH), 8.00 (d, 1 H,
- = 8.20 Hz, Harom), 9.73 (br s, 1 H, NH), 12.00 (br s, 1 H, NH).
13C NMR (100 MHz, CDCl3): d = 121.96, 127.56, 129.09, 138.11,
179.40 (C=S), 189.55 (C=S) .
MS (EI, 70 eV) : P/] (%) = 196 (M+, 100), 136 (M+ – CSNH2, 56),
77 (89).
HRMS: P/] calc. for C8H8N2S2 196.0129, found 196.0134.
1ꢅꢌꢂꢅ0HWKR[\SKHQ\OꢉGLWKLRR[DPLGHꢄꢌꢃEꢉ
Red needles (45%); mp 138–140°C (light petroleum/CH2Cl2) (Lit.9b
mp 142–143°C).
UV (EtOH): lmax (log e) = 237 (4.18), 324 (4.05), 397 nm (3.84).
IR (KBr): n = 3322, 3221, 3028, 2835, 1594, 1547, 1506, 1450,
1242, 1171, 1033 cm–1
.
1H NMR (400 MHz, CDCl3): d = 3.01 (s, 3 H, CH3O), 6.97 (d, 2 H,
- = 8.90 Hz), 7.87 (br s, 1 H, NH), 7.95 (d, 2 H, - = 8.90 Hz), 9.77
(br s, 1 H, NH), 11.96 (br s, 1 H, NH) .
MS (EI, 70 eV): P/] (%) = 226 (M+, 100), 195 (M+ – CH3O, 17),
It is also possible, though perhaps less likely, that the
LAH reaction could be intramolecular. Thus the anion of
166 (M+ – CSNH2, 31).
HRMS: P/] calc. for C9H10N2OS2 226.0234, found 226.0238.
ꢊ (Scheme 2) could cyclise to give the dithietane11
ꢋ
1ꢅꢌꢁꢆꢂꢆꢃꢅ7ULPHWKR[\SKHQ\OꢉGLWKLRR[DPLGHꢄꢌꢃFꢉꢄ
Orange needles (35%); mp 176–178°C (light petroleum/CH2Cl2).
which should then be rapidly reduced with cleavage of the
disulfide bond to give dithiooxamide ꢃ.
UV (EtOH): lmax (log e) = 322 (3.99), 398 nm (3.79).
The simple method described here for the conversion of a
primary aromatic amine into the corresponding 1-
aryldithiooxamide ꢃ has the advantage of giving none of
the symmetrical compound, ArNHCSCSNHAr.
IR (KBr): n = 3290, 3145, 1595, 1531, 1505, 1430, 1236,
1123 cm–1.
1H NMR (400 MHz, DMSO): d = 3.66 (s, 3 H, CH3O), 3.75 (s, 6 H,
2 × CH3O), 7.45 (s, 2 H, Harom), 9.80 (br s, 1 H, NH), 10.34 (br s, 1
H, NH), 11.94 (1 H, br s, NH) .
Synthesis 1999, No. 8, 1345–1348 ISSN 0039-7881 © Thieme Stuttgart · New York

3$3(5
Convenient Synthesis of Dithiooxamides from 1-Arylimino-1,2,3-dithiazoles
ꢀꢁꢂꢋ
13C NMR (100 MHz, DMSO): d = 55.91, 60.92, 100.25, 134.51,
135.68, 152.41, 188.80 (C=S), 195.11(C=S) .
MS (EI, 70 eV : P/] (%) = 254 (M+, 100), 194 (M – CSNH2, 27),
162 (M – CSNH2 – S, 27) .
MS (EI, 70 eV): P/] (%) = 286 (M+, 100), 226 (M+ – CSNH2, 24).
HRMS: P/] calc. for C10H10N2O2S2 254.0183, found 254.0182.
HRMS: P/] calc.for C11H14N2O3S2 286.0446, found 286.0458.
1ꢅꢌ4XLQROLQꢅꢍꢅ\OꢉGLWKLRR[DPLGHꢄꢌꢃKꢉꢄ
Orange needles (16%); mp 204°C (light petroleum/CH2Cl2).
1ꢅꢌꢇꢅ&KORURSKHQ\OꢉGLWKLRR[DPLGHꢄꢌꢃGꢉꢄ
Red needles (25%); mp 152–154°C (petroleum ether/CH2Cl2)
(Lit.9c mp 154–155°C).
UV (EtOH): lmax (log e) = 242 (4.40), 287 (4.01), 332 (4.04), 390
nm (3.87).
UV (EtOH): lmax (log e) = 235 (4.11), 326 (4.01), 376 nm (3.58).
IR (KBr): n = 3285, 3128, 1594, 1528, 1489, 1420, 1324, 1081,
1027 cm–1.
IR (KBr): n = 3309, 3210, 3118,1598, 1518, 1441, 1370, 1226,
1041, 880 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.55 (dd, 1 H, - = 4.20, 8.25 Hz,
H-3), 7.63 (t, 1 H, - = 8.10 Hz, Harom), 7.76 (dd, 1 H, - = 1.20, 8.25
Hz, Harom), 7.80 (br s, 1 H, NH), 8.23 (dd, 1 H, - = 1.70, 8.25 Hz, H-
4), 9.01 (dd, 1 H, - = 1.70, 4.20 Hz, H-2), 9.68 (br s, 1 H, NH), 9.85
(dd, 1 H, - = 1.70, 7.30 Hz, Harom), 14.35 (br s, 1 H, NH).
13C NMR (100 MHz, CDCl3): d = 117.50, 122.21, 125.73, 126.51,
128.11, 134.71, 136.35, 140.58, 149.25, 178.59 (C=S), 190.42
(C=S).
1H NMR (400 MHz, CDCl3): d = 7.26 (dt, 1 H, - = 7.60 Hz, - = 1.50
Hz, Harom), 7.37 (dt, 1 H, - = 7.65, 1.50 Hz, Harom), 7.51 (dd, 1 H,
- = 8.10, 1.50 Hz, Harom), 7.75 (br s, 1 H, NH), 8.85 (dd, 1 H, - =
8.10, 1.50 Hz, Harom), 9.65 (br s, 1 H, NH), 12.48 (br s, 1 H, NH) .
13C NMR (100 MHz, CDCl3): d = 122.73, 127.16, 127.62, 128.11,
129.89, 135.19, 180.28 (C=S), 189.37 (C=S) .
MS (EI, 70 eV): P/] (%) = 230 (M+, 10), 195(M+ – Cl, 10), 170 (M+
– CSNH2, 17).
MS (EI, 70 eV): P/] (%) = 247 (M+, 28), 187 (M+ – CSNH2, 100).
HRMS: P/] calc. for C11H9N3S2 247.0238, found 247.0244.
HRMS: P/] calc. for C8H7ClN2S2 229.9739, found 229.9737.
1ꢅꢌ4XLQROLQꢅꢁꢅ\OꢉGLWKLRR[DPLGHꢄꢌꢃLꢉꢄ
Orange needles (40%); mp 212°C (light petroleum/CH2Cl2).
1ꢅꢌꢁꢆꢂꢅ'LIOXRURSKHQ\OꢉGLWKLRR[DPLGHꢄꢌꢃHꢉꢄ
Orange needles (43%); mp 137–138°C (light petroleum/CH2Cl2).
UV (EtOH): lmax (log e) = 246 (4.32), 297 (3.98), 328 (3.96), 380
1H NMR (400 MHz, CDCl3): d = 7.20–7.30 (m, 1 H, Harom), 7.50–
7.58 (m, 1 H, Harom, HF), 7.82 (br s, 1 H, NH), 8.20–8.27 (m, 1 H,
Harom., HF), 9.64 (1 H, br s, NH), 12.01 (1 H, br s, NH) .
13C NMR (100 MHz, CDCl3): d = 111.90, 112.11, 117.39, 117.57,
119.90, 119.93, 119.96, 120.00, 135.48, 135.51, 135.56, 135.60,
145.86, 145.99, 147.22, 147.25, 148.31, 148.43, 149.65, 149.79,
192.07 (C=S), 195.91 (C=S).
nm (3.69).
IR (KBr): n = 3278, 3123, 1618, 1536, 1490, 1378, 1238,
1128 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.61 (t, 1 H, - = 7.65 Hz, Harom),
7.76 (t, 1 H, - = 7.65 Hz, Harom), 7.85 (br s, 1 H, NH), 7.90 (d, 1 H,
d, - = 8.10 Hz, Harom), 8.12 (d, 1 H, - = 8.70 Hz, Harom), 9.05 (d, 1
H, - = 2.70 Hz, Harom), 9.44 (d, 1 H, - = 2.70 Hz, Harom), 9.65 (br s,
1 H, NH), 12.31 (br s, 1 H, NH).
13C NMR (100 MHz, CDCl3): d = 125.73, 127.30, 127.71, 128.30,
129.34, 129.92, 131.76, 145.56, 146.51, 180.29 (C=S), 188.85
(C=S).
MS (EI, 70 eV): P/] (%) = 232 (M+, 60), 198 (M+ – H2S, 40), 171
(M+ – HCN, – H2S, 100).
HRMS: P/] calc. for C8H6F2N2S2 231.9940, found 231.9954.
1ꢅꢌꢇꢅ+\GUR[\HWK\OSKHQ\OꢉGLWKLRR[DPLGHꢄꢌꢃIꢉꢄ
Orange needles (40%); mp 100°C (light petroleum/CH2Cl2).
MS (EI, 70eV): P/] (%) = 247 (M+, 100), 187 (M+ – CSNH2, 51),
128 (64) .
UV (EtOH): lmax (log e) = 232 (3.96), 322 nm (3.96).
IR (KBr): n = 3430, 3292, 3096, 1598, 1512, 1442, 1365, 1254,
HRMS: P/] calc. for C11H9N3S2 247.0238, found 247.0244.
1179, 1041 cm–1.
1H NMR (400 MHz, DMSO-G6): d = 2.70 (t, 2 H, - = 6.60 Hz, CH2),
3.61 (t, 2 H, - = 6.60 CH2), 4.85 (br s, 1 H, OH), 7.24–7.37 (m, 3 H,
$FNQRZOHGJHPHQW
H
arom), 7.48–7.53 (m, 1 H, Harom), 9.78 (s, 1 H, NH), 10.43 (s, 1 H,
We thank OHꢀ&RPLWpꢀGHꢀ&KDUHQWHꢅ0DULWLPHꢀGHꢀODꢀ/LJXHꢀFRQWUHꢀOH
&DQFHU for financial support, and the Wolfson Foundation for esta-
blishing the Wolfson Centre for Organic Chemistry in Medical Sci-
ence at Imperial College.
NH), 11.89 (s, 1 H, NH) .
13C NMR (100 MHz, DMSO): d = 34.38, 61.54, 126.00, 126.43,
127.53, 130.46, 135.65, 137.61, 190.23 (C=S), 193.55 (C=S).
MS (EI, 70 eV): P/] (%) = 240 (M+, 100), 222 (M+ – H2O, 42), 162
(M+ – H2O – CSNH2, 25), 128 (75), 118 (72).
5HIHUHQFHV
HRMS: P/] calc. for C10H12N2OS2 240.0362, found 240.0391.
(1) (a) Appel, R.; Janssen, H.; Siray, M.; Knoch, S. &KHPꢆꢀ%HUꢆ
ꢀꢎꢍꢃ, ꢂꢂꢇ, 1632.
(b) Review: Rees, C.W. -ꢆꢀ+HWHURF\FOꢆꢀ&KHPꢆ ꢀꢎꢎꢇ, ꢈꢃ, 639.
(2) (a) Besson, T.; Dozias, M.-J.; Guillard, J.; Rees, C.W. -ꢆꢀ
&KHPꢆꢀ6RFꢆꢀ3HUNLQꢀ7UDQVꢀꢂ ꢀꢎꢎꢍꢆꢄ3925.
1ꢅꢌꢇꢆꢁꢅ'LK\GURꢅꢀꢆꢂꢅEHQ]RGLR[DQꢅꢊꢅ\OꢉGLWKLRR[DPLGHꢄꢌꢃJꢉꢄ
Red needles (37%); mp 172°C (light petroleum/CH2Cl2).
UV (EtOH): lmax (log e) = 271 (3.92), 319 (3.97), 402 nm (3.79).
IR (KBr): n = 3296, 3152, 1603, 1537, 1502, 1321, 1285, 1246,
(b) Besson, T.; Guillaumet, G.; Lamazzi, C.; Rees, C.W.;
Thiéry, V. -ꢆꢀ&KHPꢆꢀ6RFꢆꢉꢀ3HUNLQꢀ7UDQVꢆꢀꢂ ꢀꢎꢎꢍ, 4057, and
references cited therein.
1167, 1126, 1063 cm–1.
1H NMR (400 MHz, CDCl3): d = 4.29 [s, 4 H, O(CH2)2O], 6.92 (d,
1 H, - = 8.70 Hz, H-8), 7.35 (dd, 1 H, - = 2.50, 8.80 Hz, H-7), 7.77
(br s, 1 H, NH), 7.82 (d, 1 H, - = 2.50 Hz, H-5), 9.75 (br s, 1 H, NH),
11.92 (br s, 1 H, NH).
13C NMR (100 MHz, CDCl3): d = 64.32, 64.41, 111.00, 115.74,
117.43, 131.90, 142.81, 143.33, 178.12 (C=S), 189.74 (C=S).
(3) English, R.F.; Rakitin, O. A.; Rees, C. W.; Vlasova, O.G. -ꢆꢀ
&KHPꢆꢀ6RFꢆꢉꢀ3HUNLQꢀ7UDQVꢆꢀꢂ ꢀꢎꢎꢋ, 201.
(4) Besson, T.; Guillard, J.; Rees, C. W.; Thiéry, V. -ꢆꢀ&KHPꢆꢀ6RFꢆꢉꢀ
3HUNLQꢀ7UDQVꢆꢀꢂ ꢀꢎꢎꢍ, 889.
(5) Lee, H.; Kim, K. %XOOꢆꢀ.RUHDQꢀ&KHPꢆꢀ6RF. ꢀꢎꢎꢇ, ꢂꢁ, 107.
(6) For a review, see : Rây, P.; Xavier, J. -ꢆꢀ,QGꢆꢀ&KHPꢆꢀ6RF. ꢀꢎꢊꢀ,
ꢁꢇ, 535.
Synthesis 1999, No. 8, 1345–1348 ISSN 0039-7881 © Thieme Stuttgart · New York

ꢀꢁꢂꢍ
T. Besson et al.
3$3(5
dithiazole ring and the possibility of diversion or loss of
hydrogen sulfide. The much lower yields of dithiooxamides ꢃ
produced in the sodium hydride reactions (Scheme 1) could
then result from substantial loss of hydrogen sulfide in the
boiling THF medium.
(7) Vagg, R. S. In &RPSUHKHQVLYHꢀ&RRUGLQDWLRQꢀ&KHPLVWU\;
Wilkinson, G., Gillard, R. D., Mc Cleverty, J. A.,Eds.;
Pergamon: Oxford; 1987, vol 2, p 800.
(8) Dell, C. P. Inꢀ&RPSUHKHQVLYHꢀ2UJDQLFꢀ)XQFWLRQDOꢀ*URXSꢀ
7UDQVIRUPDWLRQV; Katritzky, A.R., Meth-Cohn, O., Rees, C.
W., Eds.; Elsevier: Oxford, 1995; Vol. 5, p 579.
(11) For a review, see: Zoller, U. In &RPSUHKHQVLYHꢀ+HWHURF\FOLFꢀ
&KHPLVWU\ꢀ,,; Katritzky, A. R., Rees, C.W., Scriven, E.
F.V.,Ed,.; Elsevier Oxford, 1996; Vol. IB, Chap. 1.35.
(9) (a) Kumelj, B.; Tisler, M. 9HVWQLNꢀ6ORYHQꢆꢀ.HPLꢆꢀ'UXöWYD
ꢀꢎꢃꢍ, ꢊ, 69; &KHPꢆꢀ$EVWUꢆ ꢀꢎꢊꢏ, ꢊꢋ, 22426.
(b) Grabenko, A. D.; Pel’kis, P. S. =KXUꢆꢀ2EVKFKHLꢀ.KLPꢆ
ꢀꢎꢊꢏ, ꢁꢌ, 1222; &KHPꢆꢀ$EVWUꢆ ꢀꢎꢊꢀ, ꢊꢊ, 1484.
(c) Grabenko, A. D.; Pel’kis, P. S. =KXUꢆꢀ2EVKFKHLꢀ.KLPꢆ
ꢀꢎꢊꢀ, ꢁꢂ, 2739; &KHPꢆꢀ$EVWUꢆ ꢀꢎꢊꢇ, ꢊꢍ, 10026.
Article Identifier:
1437-210X,E;1999,0,08,1345,1348,ftx,en;P01099SS.pdf
(10) The relatively low yields observed could result from the
alternative sites available for nucleophilic attack on the
Synthesis 1999, No. 8, 1345–1348 ISSN 0039-7881 © Thieme Stuttgart · New York