Reaction of 4-Iodo-3-(2-iodoaryl)sydnones with Sodium Sulfite and Sodium Borohydride

Full text of DOI:10.1080/00304948.2016.1206436

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
ISSN: 0030-4948 (Print) 1945-5453 (Online) Journal homepage: http://www.tandfonline.com/loi/uopp20
Reaction of 4-Iodo-3-(2-iodoaryl)sydnones with
Sodium Sulfite and Sodium Borohydride
Nigel N. Chitiyo, Avafia Y. Dossa, Christopher M. Jackson, Lihong Sun &
Kenneth Turnbull
To cite this article: Nigel N. Chitiyo, Avafia Y. Dossa, Christopher M. Jackson, Lihong Sun &
Kenneth Turnbull (2016) Reaction of 4-Iodo-3-(2-iodoaryl)sydnones with Sodium Sulfite and
Sodium Borohydride, Organic Preparations and Procedures International, 48:5, 405-412, DOI:
10.1080/00304948.2016.1206436
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Date: 23 September 2016, At: 06:52

Organic Preparations and Procedures International, 48:405–412, 2016
Copyright Ó Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2016.1206436
Reaction of 4-Iodo-3-(2-iodoaryl)sydnones with
Sodium Sulfite and Sodium Borohydride
Nigel N. Chitiyo, Avafia Y. Dossa, Christopher M. Jackson,
Lihong Sun, and Kenneth Turnbull
Department of Chemistry, Wright State University, Dayton, OH 45435, USA
Sydnones (e. g. 1) are members of the class of compounds known as mesoionic1 and they
have been studied extensively.2 Previous results from our group demonstrated that the
debromination of 4-bromo-3-arylsydnones to 3-arylsydnones may be effected using
sodium borohydride,3 sodium dithionite4 or sodium sulfite.5 More recently, we have
extended the utility of the latter reagent to the selective removal of an iodine attached to
the C4 carbon of the sydnone ring in the presence of an o-aryl-attached iodine (e. g. 2a to
3a).6 The present article is a further extension of this protocol and related ones.
R
R
R
I
I
I
3
Na2SO3
1) BuLi or LDA
2) I2
N
N
N
N
N
4
N
2
5
O
O
O
O
1
O
O
1 a-g
2 a-g
3 a-g
a, R = H; b, R = 4-Br; c, R = 3-Cl; d, R = 4-Cl; e, R = 4-CH3; f, R = 4-CH3O; g, R = 3,5-diCH3O
To examine the deiodination of the diiodo species, it was necessary to prepare sev-
eral substituted analogs 2b–g. It was anticipated that the latter would be available via
modifications of our previously reported dilithiation protocol7 involving treatment of
the parent sydnone 1a with nBuLi at low temperature followed by addition of I2 to give
2a. However, it was anticipated that this approach might be problematic for any syd-
none bearing a bromine atom on the aryl ring (e. g. 1b), wherein competitive metal-hal-
ogen exchange could occur, and we were aware that the chloro-containing species (cf.
1c and 1d) might suffer a similar fate. Further, for those sydnones containing at least
one methoxy group (e. g. 1f and 1g), directed lithiation, especially of the latter com-
Received March 29, 2016; in final form May 31, 2016.
Address correspondence to Kenneth Turnbull, Department of Chemistry, Wright State Univer-
sity, Dayton, OH 45435, USA. E-mail: kenneth.turnbull@wright.edu
405

406
Turnbull et al.
pound (1g), might result in arylsydnones with different substitution patterns from the
compounds targeted.
With these caveats in mind, we first examined the dilithiation/iodination of 3-(4-
tolyl)sydnone (1e). Gratifyingly, reaction of 1e with nBuLi (3.4 eq) at ¡78ꢀC, followed
by treatment with iodine (2.2 eq), gave the corresponding diiodo species 2e in 75%
yield. Extension of the protocol to the para-chloro analog 1d afforded 2d in 54% yield.
Similar conversions of 1f (to 2f) and 1g (to 2g) were accomplished in 88% and 86%
yield, respectively, using three equivalents of both nBuLi and iodine at ¡45ꢀC. As men-
n
tioned above, for the meta-chloro species 1c the use of BuLi appeared imprudent; it
was hoped that the acidity of the aryl hydrogen flanked by both the chlorine and the syd-
none ring might be increased sufficiently to allow the removal of that proton by a non-
nucleophilic base such as lithium diisopropylamide (LDA) without inducing metal-hal-
ogen exchange. In the event, treatment of 1c with LDA (2.2 eq.) at ¡78ꢀC followed by
the addition of iodine (2.2 eq.) afforded the diiodo compound 2c in 75% yield. Unfortu-
nately but not surprisingly, extension of the LDA/I2 protocol to the para-bromo syd-
none 1b was considerably less successful; the resultant product mixture had to be
subjected to multiple column chromatography to afford the desired product 2b in only
35% yield.
With the diiodosydnones in hand, the generality of the selective removal of the syd-
none-attached iodine using sodium sulfite in methanol was explored first. We had
employed sodium sulfite previously as a reagent for the conversion of diiodosydnone
2a to monoiodo sydnone 3a.6 In all cases, treatment of the diiodosydnones 2b-2g with
aqueous sodium sulfite in methanol afforded the corresponding ortho-iodoaryl sydnones
3b-3g in good to high yields (75–95%) and high purity. The identity of the products was
confirmed by satisfactory combustion analyses, the presence of the sydnone CHO
stretching vibration at »1750 cm¡1 and the expected chemical shifts and splitting pat-
terns in their proton and carbon NMR spectra. For the latter, the most telling observa-
tion was the shift in the position of the sydnone C-4 position from ca. 54 ppm (d) to ca.
95 ppm (d), indicating the loss of an iodine from that position.
This reductive approach allows the preparation of species 3a–g, which would be dif-
ficult to prepare by other methods and, since the ortho-iodo species 3a has proven to be
an attractive template for iterative Sonogashira coupling procedures, leading to sydnone-
containing oligomeric areneynes as ligands for potential non-linear optical materials,6 we
anticipate that the present extension will greatly facilitate the preparation of the latter
species.
Further, since we had employed sodium borohydride previously as a reagent for the
facile removal of a C-sydnone-attached bromine,3 it was of interest to determine if
selective deiodination could be effected with this reagent as well. Surprisingly, when
diiodosydnone 2a was treated with sodium borohydride in methanol at room tempera-
ture, rapid (TLC evidence) removal of both iodine atoms occurred to afford 3-phenyl-
sydnone (1a) in 73% yield. The procedure proved to be rather general and exposure of
diiodosydnones 2d–2g to the reagent under the same conditions gave the corresponding
deiodinated compounds 1d–1g in 86–92% yields. While the lability of groups attached
to the sydnone 4-position is well known4,5, to the best of our knowledge this is the first
example of removal of an o-aryl attached group (in a 3-arylsydnone) by a nucleophilic
reducing agent. It is reasonable to assume that the strong electron-withdrawing effect of
the sydnone N-3 position activates the ortho-position to nucleophilic displacement, but
confirmation of this speculation will require further mechanistic studies.

4-iodo-3-(2-iodoaryl)sydnones
407
R
R
I
NaBH4
N
N
I
N
N
O
O
O
O
2 a, d-g
1 a, d-g
a, R = H; d, R = 4-Cl; e, R = 4-CH3; f, R = 4-CH3O; g, R = 3,5-diCH3O
In conclusion, the sydnone dilithiation/iodination approach7 has been extended and
modified for the preparation of a number of aryl substituted diiodosydnones 2a–g. Selec-
tive deiodination of the latter (to yield the ortho-iodo species 3a–g) may be achieved in
high yields under mild conditions. A novel, complete deiodination of 2a,d–g to 1a,d–g
has been developed.
Experimental Section
3-Phenylsydnone (1a) was synthesized from N-phenylglycine using a literature proce-
dure.8 The other starting sydnones, 3-(4-bromophenyl)sydnone (1b),9 3-(3-chlorophenyl)
sydnone (1c),10 3-(4-chlorophenyl)sydnone (1d),11 3-(4-tolyl)sydnone (1e),11 3-(4-
methoxyphenyl)-sydnone (1f)12 and 3-(3,5-dimethoxyphenyl)sydnone (1g)13 were pre-
pared according to the reported procedure.13 4-Iodo-3-(2-iodophenyl)sydnone (2a) was
prepared from 3-phenylsydnone.7 All other starting materials and reagents were pur-
chased commercially and used without purification unless otherwise noted. Melting
points were determined on a Mel-Temp melting point device and are uncorrected. The
infrared spectra were taken as KBr pellets on a Nicolet 6700 FTIR. NMR spectra were
obtained on a Bruker Avance 300 MHz NMR and are reported relative to tetramethylsi-
lane (TMS) as an internal standard. Elemental analyses were carried out by Midwest
Microlab LLC, Indianapolis, IN 46250.
3-(4-Bromo-2-iodophenyl)-4-iodosydnone (2b)
To a stirred solution of 3-(4-bromophenyl)sydnone (1b, [0.10 g, 0.42 mmol]) in dry THF
(40 mL) under an atmosphere of dry nitrogen at ¡40ꢀC LDA (1.07 M, 1.00 mL,
1.00 mmol) was added dropwise. After 0.5 h, iodine (0.224 g, 0.88 mmol) was added in
one portion and, after an additional 2.0 h, the mixture was allowed to warm to 0ꢀC where-
upon it was quenched with saturated brine (70 mL) then extracted with CH2Cl2 (2 £
50 mL). The combined layers were washed with aqueous sodium sulfite (5%, 2 £
50 mL), dried (MgSO4) and evaporated in vacuo to yield an oil, which was purified by
column chromatography (SiO2, CH2Cl2 as eluent) to afford 2b as colorless crystals
(0.071 g, 35%), mp. 170–172ꢀC. IR: 1745, 1726 (sydnone CHO), 1566, 1471 cm¡1. 1H-
NMR (DMSO-d6): d 8.46 (s, 1 H), 7.99 (d, 1 H), 7.82 (d, 1 H). 13C-NMR (DMSO-d6): d
168.77 (sydnone CHO), 141.71, 137.26, 133.02, 129.41, 126.64, 97.79, 59.70 (sydnone
C-4).

408
Turnbull et al.
Anal. Calcd. for C8H3BrI2N2O2: C, 19.50; H, 0.61; N, 5.68. Found: C, 19.39; H, 0.56;
N, 5.45.
3-(3-Chloro-2-iodophenyl)-4-iodosydnone (2c)
To a stirred solution of 3-(3-chlorophenyl)sydnone 1c [0.20 g, 1.02 mmol] in dry THF
(30 mL) under an atmosphere of dry nitrogen at ¡78ꢀC was added LDA (1.50 mL,
1.49 M, 2.24 mmol) dropwise. After 0.5 h, iodine (0.568 g, 2.24 mmol) was added and,
after 3 h in total, the reaction was warmed to 0ꢀC, quenched with saturated brine (70 mL)
then extracted with CH2Cl2 (2 £ 50 mL). The combined layers were dried (MgSO4) and
evaporated in vacuo to yield an oil, which afforded light yellow crystals upon trituration
with diethyl ether. Further purification by column chromatography (SiO2, CH2Cl2 as elu-
ent) gave 2c as colorless crystals (0.343 g, 75%), mp. 156–157ꢀC. IR: 1722 (sydnone
CHO), 1455, 1192 cm¡1. 1H-NMR (DMSO-d6): d 7.80 (m, 2 H), 7.99 (d, 1 H). 13C-NMR
(DMSO-d6): d 169.55 (sydnone C D O), 102.99, 47.05 (arom C), 140.58, 133.60, 131.91,
127.32 (arom C-H), 60.81 (sydnone C-4).
Anal. Calcd. for C8H3ClI2N2O2: C, 21.44; H, 0.67; N, 6.25. Found: C, 21.53; H, 0.65;
N, 6.05.
3-(4-Chloro-2-iodophenyl)-4-iodosydnone (2d)
To a stirred solution of 3-(4-chlorophenyl)sydnone (1d) [0.10 g, 0.51 mmol) in dry THF
n
(50mL) under an atmosphere of dry nitrogen at ¡78ꢀC was added BuLi (1.6 M in hex-
ane, 1.1 mL, 1.71 mmol) dropwise. After an additional 1 h, iodine (0.324 g, 1.28 mmol)
was added in one portion. The reaction was left overnight after which time the contents
were poured into saturated brine (100 mL) and, after the residual THF had evaporated,
the mixture was extracted with dichloromethane (3 £ 50 mL). The combined layers were
washed with aqueous sodium sulfite (50 mL, 5%), dried (MgSO4), filtered and evaporated
in vacuo to yield an oil which was subjected to column chromatography (SiO2, dichloro-
methane as eluent) and recrystallized from dichloromethane / hexanes to yield 2d as col-
1
orless crystals (0.122 g, 54%), mp.145–146ꢀC. IR: 2915, 1714 (CHO), 1589 cm¡1. H-
NMR (CDCl3): d 8.03 (s, 1 H), 7.55 (d, 1 H), 7.31 (d, 1 H). 13C-NMR (CDCl3): d 168.38
(sydnone CHO), 140.28, 139.45, 136.65, 130.13, 128.16, 94.51, 52.96 (sydnone C-4).
Anal. Calcd. for C8H3ClI2N2O2: C, 21.44; H, 0.67; N, 6.25. Found: C, 21.39; H, 0.76;
N, 5.94.
4-Iodo-3-(2-iodo-4-methylphenyl)sydnone (2e)
To a stirred solution of 3-(4-methylphenyl)sydnone (1e) [0.10 g, 0.57 mmol] in dry THF
(50 mL) under an atmosphere of dry nitrogen at ¡78ꢀC was added nBuLi (1.6 M in hex-
ane, 1.2 mL, 1.94 mmol) dropwise. After 1 h, iodine (dried over P2O5, 0.324 g,
1.28 mmol) was added. After an additional 12 h, during which time the mixture was
allowed to warm to room temperature, the mixture was poured into saturated brine
(100 mL) and, after the residual THF had evaporated, the mixture was extracted with
dichloromethane (3 £100 mL). The combined layers were washed with aqueous sodium
sulfite (50 mL, 5%), dried (MgSO4), filtered and evaporated in vacuo to yield an oil,
which upon crystallization from dichloromethane / hexanes afforded 2e as colorless crys-
tals (0.182 g, 75%), mp.188–190ꢀC. IR: 2922, 1708 (sydnone CHO), 1570, 1474 cm¡1
.
1H-NMR (CDCl3): d 7.89 (s, 1 H), 7.43 (d, 1 H), 7.23 (d, 1 H), 2.40 (s, 3 H). 13C-NMR

4-iodo-3-(2-iodoaryl)sydnones
409
(CDCl3): d 168.60 (sydnone C D O), 144.84, 141.06, 130.43, 127.01, 124.79, 93.51, 53.03
(sydnone C-4), 21.04.
Anal. Calcd. for C9H6I2N2O2: C, 25.26; H, 1.41; N, 6.55. Found: C, 25.56; H, 1.66;
N, 6.34.
4-Iodo-3-(2-iodo-4-methoxyphenyl)sydnone (2f)
To a stirred solution of 3-(4-methoxyphenyl)sydnone (1f) [0.15 g, 0.77 mmol] in dry
THF (50 mL) under an atmosphere of dry nitrogen at ¡45ꢀC was added nBuLi (1.6 M in
hexane, 1.5 mL, 2.31 mmol) dropwise. After 0.5 h, iodine (dried over P2O5, 0.586 g,
2.31 mmol) was added. After an additional 1 h, the mixture was allowed to warm to 0ꢀC
whereupon it was quenched with saturated brine (50 mL) then extracted with CH2Cl2 (3
£ 40 mL). The combined layers were washed with aqueous sodium sulfite (200 mL,
5%), dried (MgSO4), filtered and evaporated in vacuo to yield an oil, which was purified
by column chromato-graphy (SiO2, CH2Cl2 as eluent). Recrystallization from dichloro-
methane / hexane afforded 2f as colorless crystals (0.304 g, 88%), mp. 128–130ꢀC. IR:
1
2916, 1745 (sydnone CHO), 1589, 1494 cm¡1. H-NMR (CDCl3): d 7.50 (d, 1 H), 7.30
(t, 1 H), 7.10 (d, 1 H), 3.90 (s, 3 H). 13C-NMR (CDCl3): d 169.0 (sydnone C D O), 162.0,
131.0, 128.0, 122.0, 115, 94.0, 56.0, 54.0 (sydnone C-4).
Anal. Calcd. for C9H6I2N2O3: C, 24.35; H, 1.36; N, 6.31. Found: C, 24.28; H, 1.40;
N, 6.16.
4-Iodo-3-(2-iodo-3,5-dimethoxyphenyl)sydnone (2g)
To a stirred solution of 3-(3,5-dimethoxyphenyl)sydnone (1g, 0.10 g, 0.45 mmol) in dry
THF (40 mL) under an atmosphere of dry nitrogen at ¡45 ꢀC was added nBuLi (1.6 M in
hexane, 0.8 mL, 1.35 mmol) dropwise. After 0.5 h, iodine (dried over P2O5, 0.343 g,
1.35 mmol) was added. After an additional 1 h, the mixture was allowed to warm to 0ꢀC
whereupon it was quenched with saturated brine (50 mL) then extracted with CH2Cl2 (3
£ 40 mL). The combined layers were washed with aqueous sodium sulfite (150 mL,
5%), dried (MgSO4) and evaporated in vacuo to yield an oil, which was purified by col-
umn chromatography (SiO2, CH2Cl2 as eluent). Recrystallization from dichloromethane /
hexane afforded 2g as colorless crystals (0.183g, 86%), mp. 231–233ꢀC. IR: 1738 (syd-
none CHO), 1576, 1452 cm¡1. 1H-NMR (DMSO-d6): d 6.90 (d, 1 H), 7.20 (d, 1 H), 4.00
(s, 3 H), 3.90 (s, 3 H). 13C-NMR (DMSO-d6): d 169.0 (sydnone CHO), 161.0, 160.0,
139.0, 106.0, 102.0, 77.0, 59.0 (sydnone C-4), 57.0, 56.0.
Anal. Calcd. for C10H8I2N2O4: C, 25.34; H, 1.70; N, 5.91. Found: C, 25.44; H, 1.59;
N, 5.79.
Reaction of Diiodosydnones 2b–g with Sodium Sulfite. General Procedure
To a solution of diiodinated sydnone (0.12–0.45 mmol) in methanol (2–4 mL) was added
a solution of sodium sulfite (0.06–0.23 g, 0.48–1.8 mmol) in water (2–4 mL). The prog-
ress of the reaction was monitored by TLC and after all the starting material had reacted
(usually 0.5 h to 1 h), the methanol was removed under a stream of air. The residual
aqueous suspension was extracted with dichloromethane (3£10 mL) and the combined
extract was washed with water (50 mL), dried over magnesium sulfate and evaporated in
vacuo. The crude products were then purified, either by column chromatography (SiO2,
dichlorometha-ne/hexanes) or recrystallization from dichloromethane/hexanes.

410
Turnbull et al.
3-(4-Bromo-2-iodophenyl)sydnone (3b)
3-(4-Bromo-2-iodophenyl)-4-iodosydnone (2b, 0.10 g, 0.20 mmol) using the general proce-
dure gave, after recrystallization, 3b as colorless crystals (0.055 g, 75%), mp. 183–184ꢀC.
1
IR: 1726 (sydnone CHO), 1576, 1483 cm¡1. H-NMR (DMSO-d6): d 8.40 (s, 1 H), 7.94
(d, 1 H), 7.82 (d, 1 H), 7.58 (s, 1 H). 13C-NMR (DMSO-d6): d 168.2 (sydnone CHO),
141.7, 136.9, 132.7, 128.7, 126.3, 98.9 (sydnone C-4), 96.4.
Anal. Calcd. for C8H4BrIN2O2: C, 26.19; H, 1.10; N, 7.63. Found: C, 25.99; H, 1.14;
N, 7.35.
3-(3-Chloro-2-iodophenyl)sydnone (3c)
3-(3-Chloro-2-iodophenyl)-4-iodosydnone (2c, 0.20 g, 0.45 mmol) using the general pro-
cedure afforded, after recrystallization, 3c as colorless crystals (0.135 g, 93%), mp. 237–
1
239ꢀC. IR: 1749 (sydnone CHO), 1562, 1475 cm¡1. H-NMR (CDCl3): d 7.77 (d, 1 H),
7.57 (t, 1 H), 7.42 (d, 1 H), 6.58 (s, 1 H). 13C-NMR (CDCl3): d 168.5 (sydnone CHO),
141.9, 139.6, 132.8, 130.3, 124.9, 98.8, 97.7 (sydnone C-4).
Anal. Calcd. for C8H4ClIN2O2: C, 29.80; H, 1.25; N, 8.69. Found: C, 29.74; H, 1.25;
N, 8.62.
3-(4-Chloro-2-iodophenyl)sydnone (3d)
3-(4-Chloro-2-iodophenyl)-4-iodosydnone (2d, 0.112 g, 0.25 mmol) using the general
procedure yielded, after recrystallization, 3d as colorless crystals (0.07 g, 87%), mp.
179–181ꢀC. IR: 3139, 1727 (sydnone CHO), 1573, 1433 cm¡1. 1H-NMR (DMSO-d6): d
8.28 (s, 1 H), 7.94 (d, 1 H), 7.81 (d, 1 H), 7.58 (s, 1 H). 13C-NMR (DMSO-d6): d 168.2
(sydnone CHO), 139.1, 137.5, 136.5, 129.7, 128.4, 98.9 (sydnone C-4), 96.1.
Anal. Calcd. for C8H4ClIN2O2: C, 29.80; H, 1.25; N, 8.69. Found: C, 29.82; H, 1.32;
N, 8.44.
3-(2-Iodo-4-methylphenyl)sydnone (3e)
4-Iodo-3-(2-iodo-4-methylphenyl)sydnone (2e, 0.05 g, 0.12 mmol) using the general pro-
cedure gave, after column chromatography, 3e as colorless crystals (0.03 g, 85%), mp.
1
134–135ꢀC. IR: 3137, 1730 (sydnone CHO), 1590, 1447 cm¡1. H-NMR (CDCl3): d
7.87 (s, 1 H), 7.38 (d, 2 H), 7.28 (d, 2 H), 6.52 (s, 1 H), 2.45 (s, 3 H). 13C-NMR (CDCl3):
d 168.7 (sydnone CHO), 144.6, 141.3, 130.4, 127.0, 126.3, 97.7 (sydnone C-4), 91.6,
21.0.
Anal. Calcd. for C9H7IN2O2: C, 35.79; H, 2.34; N, 9.27. Found: C, 35.47; H, 2.60; N,
9.53.
3-(2-Iodo-4-methoxyphenyl)sydnone (3f)
4-Iodo-3-(2-iodo-4-methoxyphenyl)sydnone (2f, 0.056 g, 0.13 mmol) using the general
procedure afforded, after recrystallization, 3f as colorless crystals (0.036 g, 95%), mp.
139–141ꢀC. IR: 3150, 1753 (sydnone CHO), 1490, 1365 cm¡1. 1H-NMR (CDCl3): d 7.5
(d, 1 H), 7.4 (d, 1 H), 7.1 (d, 1 H), 6.5 (s, 1 H), 3.9 (s, 3 H). 13C-NMR (CDCl3): d 169
(sydnone CHO), 162, 131, 127, 126, 115, 98 (sydnone C-4), 92, 56.

4-iodo-3-(2-iodoaryl)sydnones
411
Anal. Calcd. for C9H7IN2O3: C, 33.99; H, 2.22; N, 8.81. Found: C, 34.05; H, 2.16; N,
8.79.
3-(2-Iodo-3,5-dimethoxyphenyl)sydnone (3g)
4-Iodo-3-(2-iodo-3,5-dimethoxyphenyl)sydnone (2g, 0.145 g, 0.30 mmol) using the gen-
eral procedure yielded, after recrystallization, 3g as colorless crystals (0.095 g, 91%),
mp. 194–196ꢀC. IR: 3145, 1597, 1454, 1327 cm¡1. 1H-NMR (DMSO-d6): d 7.5 (s, 1 H),
7.2 (s, 1 H), 7.1 (s, 1 H), 3.9 (s, 3 H), 3.8 (s, 3 H). 13C-NMR (DMSO-d6): d 168 (sydnone
CHO), 161, 160, 139, 105, 102, 96 (sydnone C-4), 76, 57, 56.
Anal. Calcd. for C10H9IN2O4: C, 34.50; H, 2.61; N, 8.05. Found: C, 34.44; H, 2.60;
N, 7.88.
Reaction of Diiodosydnones 2a,d–g with Sodium Borohydride. General Procedure
To a stirred solution of the diiodinated sydnone 2a,d–g (0.11–0.36 mmol) in methanol
(1–3 mL) was added sodium borohydride (0.042–0.136 g, 1.1–3.6 mmol) in three por-
tions over 15 min. The progress of the reaction was monitored by TLC and after all the
starting material had reacted (usually <0.5 h), methanol was removed under a stream of
air. The residue was treated with water (2–4 mL) and the resultant precipitate was col-
lected in vacuo and dried to yield the nearly pure products 1a,d–g.
3-Phenylsydnone (1a)
4-Iodo-3-(2-iodophenyl)sydnone (2a, 0.150 g, 0.362 mmol) using the general procedure
afforded 1a as colorless crystals (0.043 g, 73%), identical to an authentic sample.
3-(4-Chlorophenyl)sydnone (1d)
3-(4-Chloro-2-iodophenyl)-4-iodosydnone (2d, 0.104 g, 0.23 mmol) using the general
procedure yielded 1d as colorless crystals (0.039 g, 86%), identical to an authentic
sample.
3-(4-Methylphenyl)sydnone (1e)
4-Iodo-3-(2-iodo-4-methylphenyl)sydnone (2e, 0.05 g, 0.117 mmol) using the general
procedure gave 1e as colorless crystals (0.018 g, 87%), identical to an authentic sample.
3-(4-Methoxyphenyl)sydnone (1f)
4-Iodo-3-(2-iodo-4-methoxyphenyl)sydnone (2f, 0.05 g, 0.11 mmol) using the general
procedure yielded 1f as colorless crystals (0.02 g, 92%), identical to an authentic sample.
3-(3,5-Dimethoxyphenyl)sydnone (1g)
Treatment of 4-iodo-3-(2-iodo-3,5-dimethoxyphenyl)sydnone (2g, 0.143 g, 0.30 mmol)
using the general procedure led to 1g as colorless crystals (0.062 g, 92%), identical to an
authentic sample.

412
Turnbull et al.
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