N-CHLOROSUCCINIMIDE

1

N-Chlorosuccinimide

N

O

O

Cl

[128-09-6]

C

4

H

4

ClNO

2

(MW 133.53)

InChI = 1/C4H4ClNO2/c5-6-3(7)1-2-4(6)8/h1-2H2
InChIKey = JRNVZBWKYDBUCA-UHFFFAOYAN

(electrophilic α-chlorination of sulfides, sulfoxides, and ketones;
preparation of N-chloroamines)

Alternate Name:

1-chloro-2,5-pyrrolidinedione; NCS.

Physical Data:

mp 144–146

◦

C.

Solubility:

sol H

2

O; sl sol CCl

4

, benzene, toluene, AcOH; insol

ether.

Form Supplied in:

white powder or crystals having a weak odor

of chlorine when pure; widely available.

Purification:

the commercial reagent acquires a light yellow color

and a rather strong odor of chlorine after long storage but is
easily recrystallized from acetic acid: rapidly dissolve 200 g of
impure sample in 1 L preheated glacial AcOH at 65–70

◦

C (3–5

min); cool to 15–20

◦

C to effect crystallization; filter through a

Buchner funnel and wash the white crystals once with glacial
AcOH and twice with hexane; dry in vacuo (>85% recovery).

Analysis of Reagent Purity:

the standard iodide–thiosulfate titra-

tion method is suitable.

Handling, Storage, and Precautions:

store under refrigeration

and protect from moisture; acutely irritating solid, with toxic
effects similar to those of the free halogens; avoid inhalation;
use an efficient fume hood; perform all operations as rapidly as
possible to avoid extensive decomposition of the reagent.

Original Commentary

Scott C. Virgil
Massachusetts Institute of Technology, Cambridge, MA, USA

N

-Chlorosuccinimide is a convenient reagent for the electro-

philic substitution and addition of chlorine to organic compounds.
Other chlorinating agents of use include Chlorine, Sulfuryl Chlo-
ride, Chloramine-T, tert-Butyl Hypochlorite, and Trichloroiso-
cyanuric Acid. The primary advantages of using NCS include the
ease in handling, the mild conditions under which chlorination
proceeds, and the ease of removal of the inoffensive byproduct
succinimide.

α

α

α

-Chlorination of Carbonyl Derivatives.

Carbonyl com-

pounds can be chlorinated in the α-position by addition of NCS
directly to the lithium enolates, enoxyborinates, or more
commonly to the silyl enol ether derivatives.

1

In combination

with methods for the regiospecific generation of enolates and silyl
enol ethers, α-chloroketones of desired structure can be produced.
For example, β-ionone can be chlorinated selectively in the α

′

-

position by addition of NCS to the kinetic enolate (eq 1).

2

With the

appropriate chiral auxiliary, NCS chlorinates silyl ketene acetals
with high levels of diastereoselectivity (eq 2).

3

α

-Chloro ketones,

α

-chloro esters, and α-chloro sulfones may also be prepared by

reaction of NCS with the β-keto derivatives and in situ deacylation
in the presence of base (eq 3).

4

NCS is also an effective reagent

for the α-chlorination of acid chlorides.

5

O

(1)

O

Cl

1. LDA, THF, 0 °C
2. NCS, –70 °C

65%

O

Et

O

SO

2

NCy

2

O

O

SO

2

NCy

2

1. LDA, TMSCl
THF, –78 °C
2. NCS, –78 °C

(2)

Cl

92%

Ph

O

CO

2

Et

Ph

Cl

CO

2

Et

NCS, NaOEt

EtOH, rt

(3)

86%

Chlorination of Sulfides and Sulfoxides.

6

The reaction of

alkyl sulfides with NCS has been used extensively for the prepa-
ration of α-chloro sulfides, and NCS is generally regarded as the
reagent of choice for the preparation of these useful synthetic
intermediates (see also Trichloroisocyanuric Acid). Since
the mechanism of chlorination involves initial formation of an
S

-chlorosulfonium salt followed by a Pummerer-like rearrange-

ment, monochlorination proceeds smoothly in CCl

4

or benzene

in the absence of added acid or base.

7

The most straightfor-

ward procedure involves the addition of NCS to a solution of the
sulfide in CCl

4

at rt or reflux, followed by removal of insoluble

succinimide by filtration. The resulting α-chloro sulfides are
easily hydrolyzed and, as this is usually undesirable, α-chloro
sulfides must be prepared under strictly anhydrous conditions
and are often used without further purification. A method has
been developed for the conversion of benzylic halides to aro-
matic aldehydes (eq 4);

8

however, this transformation is more

conveniently effected in one operation with other reagents (see
Hexamethylenetetramine). Many advantages have led to the
preferred use of NCS in the Ramberg–Bäcklund rearrangement
sequence (eq 5), which has been recently reviewed.

9

t

-Bu

t

-Bu

Br

t

-Bu

CHO

t

-Bu

(4)

1. NaSPh
2. NCS, CCl

4

3. Na

2

CO

3

(aq)

85%

S

S

Cl

(5)

NCS
CCl

4

reflux

2 steps

79%

The chlorination of trimethylsilylmethyl sulfides with NCS and

trifluoroacetic acid affords the product of chlorodesilation in high
yield.

10

The degradation of carboxylic acids to ketones can be

achieved by α-sulfenation followed by reaction with NCS in the
presence of NaHCO

3

(eq 6).

11

The S-chlorosulfonium ion inter-

mediate undergoes a decarboxylative Pummerer-like rearrange-
ment to afford the ketone upon hydrolysis. α-Phenylthio esters

Avoid Skin Contact with All Reagents

2

N-CHLOROSUCCINIMIDE

and amides can be successfully α-chlorinated using NCS in CCl

4

at 0

◦

C (eq 7).

12

1,3-Dithianes are deprotected to afford ketones

by reaction with NCS alone or in combination with Silver(I)
Nitrate in aqueous acetonitrile (see also N-Bromosuccinimide,
Mercury(II) Chloride, 1,3-Diiodo-5,5-dimethylhydantoin).

13

MeO

CO

2

H

H

MeO

CO

2

H

SMe

(6)

MeO

LDA (2 equiv)

O

NCS

64%

EtOH, NaHCO

3

HMPA, THF

then MeSSMe

N

(7)

O

NCS

CCl

4

, 0 °C

SPh

N

O

SPh

Cl

100%

Sulfides can be oxidized to sulfoxides by reaction with NCS in

methanol (0

◦

C, 1 h).

14

Similarly, selenides couple with amines

when activated by NCS to form selenimide species. These have
been generated from allylic selenides in order to prepare allylic
amines and chiral secondary allylic carbamates by [2,3]-sigma-
tropic rearrangement (eq 8).

15

(8)

NCS, Cbz-NH

2

NEt

3

, MeOH, 0 °C

PhSe

Ph

Ph

NHCbz

69%

The α-chlorination of sulfoxides is generally performed in

dichloromethane in the presence of a base (either K

2

CO

3

or pyri-

dine) and proceeds more slowly than the reactions with sulfides.

16

α

-Chloro sulfoxides bearing high optical purity at sulfur are espe-

cially useful in asymmetric synthesis, but unfortunately the chlo-
rination of optically active sulfoxides is generally accompanied
by significant racemization at sulfur. Alternate procedures are
available for achieving chlorination with predominant retention
or inversion.

17

Using NCS and Potassium Carbonate the degree

of racemization is minimized and chloromethyl p-tolyl sulfoxide
can be prepared in 87% ee and 91% chemical yield (eq 9).

18

Me

S

O

Tol

S

O

Tol

(9)

:

NCS, K

2

CO

3

CH

2

Cl

2

, rt, 40 h

Cl

:

91%, 87% ee

Reaction with Vinylic and Acetylenic Derivatives. NCS is

a suitable source of chlorine for the conversion of vinylcopper
and other organometallic derivatives to the corresponding vinyl
chlorides.

19

(E)-(1-Chloro-1-alkenyl)silanes are available from

the appropriate 1-trimethylsilylalkynes by hydroalumination with
Diisobutylaluminum Hydride followed by direct treatment of the
vinylaluminum intermediate with NCS in ether at −20

◦

C (eq 10)

(the corresponding (Z)-isomer is obtained by NBS-catalyzed iso-
merization of the (E)-isomer).

20

1-Chloroalkynes can be prepared

by reaction of the corresponding lithium acetylides with NCS in
THF.

21

TMS

Bu

TMS

Al(i-Bu)

2

Bu

TMS

Cl

Bu

(10)

DIBAL

84%

– 20 °C

Et

2

O, 40 °C

NCS

Chlorination of Aromatic Compounds. NCS has also been

used for the chlorination of pyrroles and indoles; however, the
reaction is less straightforward than when NBS and N-Iodosuccin-
imide are used.

22

In the chlorination of 1-methylpyrrole, it has

been demonstrated that basic conditions (NaHCO

3

, CHCl

3

) lead

to the formation of 1-methyl-2-succinimidylpyrrole (eq 11).

23

In

the presence of catalytic amounts of perchloric acid, thiophenes
and other electron-rich aromatic compounds have been chlori-
nated with NCS.

24

(N-Chlorosuccinimide–Dimethyl Sulfide is

used for the selective o-substitution of phenols.)

N

Me

N

Me

Cl

N

Me

N

O

O

(11)

NCS, rt

+

THF
CHCl

3

, NaHCO

3

89%

–

3%

76%

Synthesis of N-Chloroamines. The conversion of secondary

amines to N-chloroamines by reaction with NCS in ether or
dichloromethane has many advantages over the use of aqueous
hypochlorite, including ease of isolation. This method has been
used repeatedly in the preparation of N-chloroamines for alkene
amination (eqs 12 and 13)

25

and other reactions.

26

1. NCS
CH

2

Cl

2

, 0 °C

2. Ag

2

O, dioxane (aq)

O

O

O

O

MeN

(12)

NH

Me

HO

59%

1. NCS
CH

2

Cl

2

, 0 °C

2. Ag

2

O, THF (aq)

(13)

BnO

BnO

NMe

H

OH

NH

Me

83%

Other Oxidation and Chlorination Reactions.

27

gem

-

Chloronitro compounds are prepared by treating nitronate
anions with NCS in aqueous dioxane, or alternatively by reac-
tion of ketoximes with NCS (eq 14).

28

Oxidative decarboxylation

of carboxylic acids with Lead(IV) Acetate and NCS has been used
effectively for the synthesis of tertiary alkyl chlorides (eq 15).

29

NCS

H

2

O, C

6

H

6

NOH

NO

2

Cl

(14)

100%

A list of General Abbreviations appears on the front Endpapers

N-CHLOROSUCCINIMIDE

3

Pb(OAc)

4

, NCS

DMF, AcOH, 50 °C

CO

2

H

Cl

(15)

95%

NCS is also regularly used for the direct oxidation of alco-

hols to ketones. The presence of Triethylamine serves to acti-
vate the reagent for rapid quantitative oxidation of catechols and
hydroquinones to o- and p-quinones, respectively, and for the oxi-
dation of benzophenone hydrazone to diphenyldiazomethane.

30

N-Chlorosuccinimide–Dimethyl Sulfide is also used in the mild
oxidation of alcohols, as well as in the conversion of allylic alco-
hols to allylic chlorides.

First Update

Terry V. Hughes
J&JPRD, Raritan, NJ, USA

α

α

α

-Chlorination of Carbonyl Derivatives. The direct chlori-

nation of β-keto esters and cyclic ketones by NCS proceeds readily
at room temperature under acid catalysis by Amberlyst-15

©

. The

reaction is general and works for acyclic, cyclic, and heterocyclic
β

-keto esters. For example, 3-oxo-3-pyridin-2-yl-propionic acid

ethyl ester was α-chlorinated in excellent yield (eq 16).

31

N

O

OEt

O

N

O

OEt

O

Cl

Amberlyst-15,

EtOAc, NCS, rt

85%

(16)

The enantioselective α-chlorination of β-keto esters was

achieved with up to 88% ee using NCS with a commercially
available TADDOL ligand.

32

The chiral bisoxazoline copper(II)

complexes have also been reported to induce the asymmetric α-
chlorination of β-keto esters when reacted with NCS.

33

The asym-

metric α-chlorination of aldehydes has been achieved using NCS
and (2R,5R)-diphenylpyrrolidine as a chiral catalyst. For example,
the enantioselective chlorination of 3-methylbutanal with NCS
proceeds in 95% yield and 94% ee (eq 17).

34

O

N
H

Ph

Ph

O

Cl

NCS, DCE, rt, 30 min

95% yield, 94% ee

(17)

The enantioselective α-chlorination reaction was also reported

to proceed for β-keto phosphonates using NCS and bisoxazoline
zinc(II) complexes in 70–91% ee.

35

Phenylselenyl chloride has

been shown to enhance the electrophilicity of NCS in chlorination
reactions. Allylic chlorination of olefins with NCS catalyzed by
PhSeCl was reported to occur with ene regiochemistry in high
yields at room temperature. For example, methyl oct-3-enoate was

smoothly converted to methyl 4-chloro-oct-2-enoate in excellent
yield with no α-chlorination to the carbonyl detected (eq 18).

36

Bu

CO

2

Me

Bu

CO

2

Me

Cl

PhSeCl, NCS, DCM, rt, 4 h

89%

(18)

Interestingly, NCS catalyzed by phenylselenyl chloride selec-

tively α-chlorinates β-keto esters in the presence of olefins with
no allylic chlorination observed (eq 19).

37

O

Ph

O

O

O

Ph

O

O

Cl

PhSeCl, NCS, MeOH, rt, 16 h

87%

(19)

Chlorination of Sulfides. The treatment of 1,3-oxathioacetals

or dithioacetals with NCS in the presence of MeOH, EtOH, 1,2-
ethanediol, or 1,3-propanediol results in the clean conversion to
the corresponding acetal or cyclic acetal. The protecting group
conversion occurs quickly and in excellent yield. For example,
the reaction of 2-phenyl-1,3-dithiolane with 1 equiv of NCS and 3
equiv of 1,2-ethanediol in dichloromethane proceeds readily to
afford 2-phenyl-1,3-dioxolane in almost quantitative yield
(eq 20).

38

S

S

O

O

NCS, 1,2-ethanediol, DCM, rt, 5 min

95%

(20)

In a similar reaction, 1,3-oxathioacetals or dithioacetals can

be deprotected with 10 mol % NCS in chloroform with 5 equiv
of DMSO to yield the corresponding carbonyl compound in
excellent yield. The reaction is chemoselective and works in the
presence of O,O-acetals.

39

Conversion of Alcohols and Thiols to Chlorides. Primary

and secondary alcohols are converted to the corresponding alkyl
chlorides with the inversion of configuration when reacted with
NCS and triphenylphosphine under Mitsunobu-type conditions.

40

The NCS and triphenylphosphine combination also transforms
certain hydroxyheterocycles to the corresponding chloroheterocy-
cle. The structural requirement for this transformation is that the
hydroxyl needs to be ortho to a nitrogen atom in the heterocycle.
For example, quinoxalin-2-ol is converted to 2-chloroquinoxaline
in good yield when treated with NCS and triphenylphosphine in
refluxing dioxane (eq 21).

41

N

N

OH

N

N

Cl

NCS, PPh

3

, dioxane, reflux

63%

(21)

Benzylic, primary, and secondary thiols are readily converted

to the corresponding alkyl chlorides when treated with NCS and
triphenylphosphine in dichloromethane. The reaction for benzylic
thiols is immediate and occurs within 24 h for secondary thiols.

Avoid Skin Contact with All Reagents

4

N-CHLOROSUCCINIMIDE

For example, α-toluenethiol is immediately converted to benzyl
chloride in 90% yield when treated with NCS and triphenylphos-
phine at room temperature (eq 22).

42

SH

Cl

NCS, PPh

3

, DCM, rt

90%

(22)

Hunsdiecker Reactions.

The Hunsdiecker reaction is the

decarboxylative halogenation of metal carboxylate salts. The
reaction of α,β-unsaturated carboxylic acids with NCS and
catalytic lithium acetate in acetonitrile–water provides the corres-
ponding β-halostyrenes in moderate yields under mild conditions.
The reaction proceeds with a good degree of stereospecificity. For
example, the reaction of 3-(4-methoxy-phenyl)-acrylic acid with
NCS with a catalytic amount of lithium acetate at room tempera-
ture provides 1-(2-chloro-vinyl)-4-methoxybenzene in good yield
(eq 23).

43

CO

2

H

MeO

Cl

MeO

NCS, LiOAc, CH

3

CN, H

2

O, rt, 6 h

65%

(23)

A modification of the Hunsdiecker reaction uses NCS

catalyzed with tetrabutylammonium trifluoroacetate (TBATFA)
and gives β-chlorostyrenes in excellent yields.

44

The use of the

NCS/TBATFA-catalyzed Hunsdiecker reaction has been extended
to various heterocyclic α,β-unsaturated carboxylic acids.

45

Aromatic Chlorination. Many aromatic and heteroaromatic

chlorinations using NCS are catalyzed by acetic acid.

46,47

Ferric

chloride and ammonium nitrite have also been used to catalyze
the chlorination of various heterocycles with NCS.

48

Although

NCS has been used for halogenation of electron-rich aromatics,
the halogenation of electron-poor aromatic systems with NCS has
been difficult to achieve. However, the chlorination of various de-
activated aromatic systems can be achieved when NCS is acid
catalyzed with boron trifluoride monohydrate. The reaction is
impressive in that even the deactivated 1-fluoro-2-nitrobenzene
is chlorinated to afford 4-chloro-1-fluoro-2-nitrobenzene in
81% yield after 18 h at 100

◦

C (eq 24).

49

NO

2

F

NO

2

F

Cl

NCS, BF

3

_

H

2

O, 100

°C, 18 h

81%

(24)

Oxidation of Alcohols. The oxidation of primary, benzylic,

and allylic alcohols to aldehydes can be selectively achieved when
the alcohol is treated with NCS catalyzed by TEMPO. Reaction
conditions are mild and do not chlorinate olefins or allylic po-
sitions. The reaction is run under typical phase-transfer condi-
tions using a dichloromethane–water mixture and TBACl as the
phase-transfer agent. The aqueous layer for the biphasic reaction is
buffered at pH 8.6 with NaHCO

3

–K

2

CO

3

. Primary alcohols were

selectively oxidized to aldehydes in the presence of secondary
alcohols and only 0–5% of the ketone resulting from oxidation
of the secondary alcohol was observed.

50

Alternatively the oxi-

dation of alcohols with NCS to the corresponding carbonyl com-
pounds can be catalyzed with N-tert-butylbenzenesulfenamide.
This reaction presumably proceeds via an initial oxidation of the
sulfur atom of the catalyst. The N-tert-butylbenzenesulfenamide-
catalyzed oxidation is selective for primary alcohols over sec-
ondary alcohols, works on a variety of substrates, and has the
advantage that it can be performed without using phase-transfer
conditions.

51

An interesting variant to the oxidation of alcohols

to carbonyl compounds with NCS is the oxidation of diols to
lactones. The reaction of 1,4-butanediol and 1,5-pentanediol with
NCS in dichloromethane at room temperature provided the corres-
ponding five- and six-membered-ring lactones in excellent yield
(eq 25).

52

HO

OH

n

n

= 2 or 3

O

O

n

n

= 1 or 2

NCS, DCM, rt, 5 h

86–88%

(25)

Miscellaneous Uses. NCS catalyzes the transesterification of

β

-keto ethyl esters with substrate alcohols under neutral condi-

tions in refluxing toluene in excellent yields. The ethanol formed
during the reaction is removed by distillation. Surprisingly, the re-
action conditions are selective and the chlorination of allylic posi-
tions or olefins is not observed. Additionally, the reaction proceeds
with only 1 equiv of the substrate alcohol allowing for complex
esters to be readily formed (eq 26).

53

MeO

OMe

OMe

O

CO

2

Et

O

O

HO

MeO

OMe

OMe

O

O

O

O

O

(26)

NCS, toluene, reflux, 7 h

81%

Oximes are converted to the corresponding carbonyl compound

when treated with NCS in CCl

4

at room temperature in excellent

yields. The workup of these deoximation reactions is especially
simple with the removal of insoluble succinimide and concentra-
tion of the solvent to afford the product carbonyl compound in high
purity. For example, 4-methoxyacetophenone oxime was readily
converted to the corresponding ketone in 4 h at room temperature
(eq 27).

54

MeO

NOH

MeO

O

NCS, CCl

4

, rt, 4 h

(27)

93%

A list of General Abbreviations appears on the front Endpapers

N-CHLOROSUCCINIMIDE

5

Alkenyl boronic acids are converted to the corresponding alkyl

chlorides when treated with NCS and TEA in good to excellent
yields. The reaction proceeds with retention of configuration at
room temperature in 30 min. For example, (E)-β-styryl boronic
acid is readily converted to (E)-β-chlorostyrene in 85% yield after
30 min at room temperature (eq 28).

55

B(OH)

2

Cl

NCS, TEA, rt, 30 min

82%

(28)

The conversion of a primary amine to the corresponding alkyl

chloride can be achieved through NCS chemistry. N-Substituted-
N

-tosylhydrazines are readily available from the reaction of

primary amines with tosyl chloride followed by subsequent
amination O-(2,4-dinitrophenyl)hydroxylamine. Treatment of N-
substituted-N-tosylhydrazines with NCS at room temperature
affords the corresponding alkyl chlorides in good yields. Solvent
choice for the reaction is critical with THF giving optimum results.
It is presumed that the chlorodeamination reaction proceeds via a
radical mechanism with the loss of nitrogen. The overall reaction
sequence for conversion of a primary amine to the corresponding
primary chloride is shown in (eq 29).

56

R

NH

2

H

2

NO

O

2

N

NO

2

R

N

Tosyl

NH

2

R

Cl

1. TosylCl

2.

NCS, THF, rt

(29)

A new synthesis of 5-chloro-1-phenyltetrazole, a useful

activating group for the hydrogenolysis of phenols, was reported
using NCS-mediated chemistry. The phase-transfer reaction of
NCS with sodium azide in chloroform generates chloroazide in
situ. The transient chloroazide reacts with phenyl isocyanide via a
1,3-dipolar cycloaddition at 0

◦

C to afford 5-chloro-1-phenyltetra-

zole in 69% yield (eq 30).

57

N

C

NCS, CHCl

3

, H

2

O, NaN

3

69%

N

N

N

N

Cl

(30)

An interesting rearrangement of cyclic dithiane alcohols to the

corresponding one-carbon ring expanded 1,2-diketones is cat-
alyzed by NCS. The reaction appears to be quite general and pro-
vides 1,2-diketones in high yields in a two-step sequence from
cyclic ketones. The two-step reaction sequence from a cyclic
ketone to a 1,2-diketone is high yielding and uses readily available
reagents (eq 31).

58

O

O

O

HO

S

S

O

O

O

n

-BuLi, 1,3-dithiane

NCS, DCM, H

2

O

74%

89%

(31)

Chlorination of dialkylphosphites with NCS affords the corres-

ponding dialkylchlorophosphate. The dialkylchlorophosphates
generated react with alcohols to give phosphonate esters. The
direct chlorination of dibenzylphosphite with NCS was used in
the synthesis of phosphate prodrugs of the anti-HIV drug 3

′

-azido-

2

′

,3

′

-dideoxythymidine (AZT) (eq 32).

59

NH

O

O

N

O

H

N

3

H

H

H

H

O

P

BnO

OBn

O

P

H

BnO

O

BnO

P

Cl

BnO

O

BnO

NCS, toluene, rt, 18h

AZT, pyridine, rt, 19 h

(32)

1.

(a) Hambly, G. F.; Chan, T. H., Tetrahedron Lett. 1986, 27, 2563. (b)
Hooz, J.; Bridson, J. N., Can. J. Chem. 1972, 50, 2387. (c) Ohkata, K.;
Mase, M.; Akiba, K., J. Chem. Soc., Chem. Commun. 1987, 1727.

2.

Vaz, A. D. N.; Schoellmann, G., J. Org. Chem. 1984, 49, 1286.

3.

Oppolzer, W.; Dudfield, P., Tetrahedron Lett. 1985, 26, 5037.

4.

Mignani, G.; Morel, D.; Grass, F., Tetrahedron Lett. 1987, 28, 5505.

5.

Harpp, D. N.; Bao, L. Q.; Black, C. J.; Gleason, J. G.; Smith, R. A., J.
Org. Chem. 1975

, 40, 3420.

6.

Dilworth, B. M.; McKervey, M. A., Tetrahedron 1986, 42, 3731.

7.

Tuleen, D. L.; Stephens, T. B., J. Org. Chem. 1969, 34, 31.

8.

Paquette, L. A.; Klobucar, W. D.; Snow, R. A., Synth. Commun. 1976,
6

, 575.

9.

Paquette, L. A., Org. React. 1977, 25, 1.

10.

Ishibashi, H.; Nakatani, H.; Maruyama, K.; Minami, K.; Ikeda, M., J.
Chem. Soc., Chem. Commun. 1987

, 1443.

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A list of General Abbreviations appears on the front Endpapers