Concomitant Desulfurization and Transesterification of Alkyl Thionocarbamates

Article abstract of DOI:10.1081/SCC-120027235

Alkyl carbamate (such as 1) reacts with triphosgene at the nitrogen atom, whereas the analogous thionocarbamates (5) react at the sulfur. Subsequent treatment with various phenols or alcohols leads to the corresponding aryl carbamates or alkyl carbamates

Full text of DOI:10.1081/SCC-120027235

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Concomitant Desulfurization and Transesterification
of Alkyl Thionocarbamates
Uday M. Joshi a b , Laxmikant N. Patkar a & Srinivasachari Rajappa a
a Division of Organic Chemistry (Synthesis) , National Chemical Laboratory , Pune, India
b Laboratoire de Synthèse Organique , 2, rue la Houssinière, BP 92208, 44322, Nantes
cedex 03, France
Published online: 16 Aug 2006.
To cite this article: Uday M. Joshi , Laxmikant N. Patkar & Srinivasachari Rajappa (2004) Concomitant Desulfurization
and Transesterification of Alkyl Thionocarbamates, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:1, 33-39, DOI: 10.1081/SCC-120027235
To link to this article: http://dx.doi.org/10.1081/SCC-120027235
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 1, pp. 33–39, 2004
Concomitant Desulfurization and
Transesterification of Alkyl
Thionocarbamates
1
Uday M. Joshi,1,2, Laxmikant N. Patkar,
*
and Srinivasachari Rajappa1
1Division of Organic Chemistry (Synthesis), National Chemical
Laboratory, Pune, India
2
`
Laboratoire de Synthese Organique,
Nantes, France
ABSTRACT
Alkyl carbamate (such as 1) reacts with triphosgene at the nitrogen atom,
whereas the analogous thionocarbamates (5) react at the sulfur.
Subsequent treatment with various phenols or alcohols leads to the
corresponding aryl carbamates or alkyl carbamates (6) respectively. The
process thus involves both desulfurization and transesterification.
Key Words: Alkyl carbamate; Aryl carbamate; Thionocarbamate;
Sulfur.
*
`
Correspondence: Uday M. Joshi, Laboratoire de Synthese Organique, 2, rue la
`
Houssiniere, BP 92208, 44322, Nantes cedex 03, France; E-mail: uday.joshi@chimie.
univ-nantes.fr.
33
DOI: 10.1081/SCC-120027235
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

34
Joshi, Patkar, and Rajappa
INTRODUCTION
We had earlier disclosed a strategy for converting alkyl carbamates to aryl
carbamates.[1–3] This was based on the use of phosphorus oxychloride in a
modified Vilsmeier reaction, during which the counter ion (Cl2), attacked the
alkyl group resulting in alkyl–oxygen cleavage.
This reaction was successfully developed into a process for the industrial
production of several aryl carbamate pesticides.[4] In a detailed exploration of
the scope and mechanism of the reaction we have now investigated the use of
reagents other than POCl3 for effecting this transformation. Earlier reports in
the literature have indicated that phosgene or oxalyl chloride may also bring
about the conventional Vilsmeier reaction.[5,6] However the former possess
serious problems in storage and handling; a better substitute would be
bis(trichloromethyl)carbonate i.e., triphosgene.[7,8] We now describe the
results on the reaction on alkyl carbamate such as 1 and alkyl thiono-
carbamates with oxygen nucleophiles in the presence of triphosgene in an
attempt to extend the scope of the transesterification.
A. Reaction of Methyl N-Methyl Carbamate (1) with
Triphosgene: Products Obtained on Treatment of the
Complex with Phenols and Benzyl Alcohol
Methyl N-methylcarbamate (1) (0.089 g, 1 mmol) was treated with
triphosgene (0.099 g, 0.33 mmol) and pyridine (0.079 g, 1 nmol) in
dichloromethane at 2108C. The resulting complex was then treated with
phenol (0.094 g, 1 mmol). Purification of the crude product by column
chromatography led to the isolation of a colorless liquid, which showed the
1
presence of both an OMe and an NMe in the H NMR spectrum. It was
therefore not the desired phenyl N-methylcarbamate, but either (2a) or (3a).
Other substituted phenols reacted similarly. The products were ultimately
shown to be the aryl esters (2) of N-methylimidodicarbonic acid methyl ester
by X-ray crystallographic analysis of the 4-bromo phenyl derivative (2c).[9] It
was thus obvious that the ambident nucleophile (1) had reacted with POCl3 at
the oxygen,[1–3] but when the electrophilic reagent was triphosgene (or the
derived phosgene analogue obtained in situ from triphosgene and pyridine)[7,8]
the site of attack was the nitrogen atom (Sch. 1). Earlier, our attempt at
converting methyl N-methylcarbamate (1) to benzyl N-methylcarbamate
using POCl3 as the reagent had proved abortive; the sole product obtained was
benzyl chloride. The use of triphosgene instead of POCl3 in this reaction again
led to the attack at nitrogen, similar to the reaction with phenols as described
above, to afford the bis carbamate (4).

Alkyl Thionocarbamates
35
Scheme 1.
B. Reaction of Alkyl Thionocarbamates with Triphosgene:
Transesterification with Phenols and Alcohols
It thus transpired that when triphosgene was the “Vilsmeier reagent,” the
initial attack on alkyl carbamates was at the nitrogen and not on the oxygen. In
the hope of changing the site of electrophilic attack, it was decided to
investigate the reactivity of alkyl thionocarbamates under the same
conditions; it was expected that in this case, the sulfur of the thiocarbonyl
group would be the preferred nucleophilic site. Earlier, it had been shown that
reaction of methyl N-methylthionocarbamate (5a) with POCl3, followed by
treatment with a-naphthol, led to carbaryl in 32% yield.[1]
Scheme 2.

36
Joshi, Patkar, and Rajappa
Table 1. Carbamates from thionocarbamates.
RNHCOOR0 (6)
R0
Entry no.
R
Yield
Reference
[2]
[2]
1
2
CH3
CH3
CH3
n-Bu
n-Bu
n-Bu
C6H5
32
16
20
39
54
45
38
61
43
54
32
68a
52
35
65a
4-ClC6H4
4-MeC6H4
C6H5
[2]
3
[10]
[10]
[11]
[10]
[10]
[12]
[2]
4
5
4-ClC6H4
4-MeC6H4
C6H5
6
7
PhCH2
PhCH2
PhCH2
CH3
8
4-ClC6H4
4-MeC6H4
PhCH2
;;
HC C–CH2
t-Bu
9
10
11
12
13
14
15
[13]
[14]
[15]
[16]
[17]
CH3
CH3
n-Bu
n-Bu
n-Bu
PhCH2
;;
HC C–CH2
t-Bu
aYield by GC.
In the event, reaction of thionocarbamates with triphosgene and pyridine
followed by addition of phenols afforded, after purification by columnchro-
matography, the corresponding aryl carbamates (6) as shown in Scheme 2
(entries 1–9 in Table 1). The most significant difference between POCl3 and
triphosgene in this series emerged during attempted transesterification of alkyl
thionocarbamates with other alcohols instead of phenols.
Reaction of methyl N-methylthionocarbamate (5a) with POCl3, followed
by treatment with benzyl alcohol still resulted in the exclusive formation of
benzyl chloride; no transesterified product could be detected. In contrast,
thionocarbamates (5) (1 mmol) when treated with triphosgene (0.099 g,
0.33 mmol) and pyridine (0.079 g, 1 mmol) in dichloromethane at 2108C
followed by alcohols (1 mmol), led to the desired alkyl carbamates (6) (entries
10–15).
EXPERIMENTAL
1H NMR spectra were recorded in CDCl3 solution on a Bruker AC200
spectrometer at 200 MHz and chemical shifts are reported in ppm downfield
from tetramethylsilane. 13C NMR spectra were recorded in CDCl3 solution on

Alkyl Thionocarbamates
37
a Bruker AC 200 or MSL 300 MHz instrument. Chemical shifts are reported in
ppm relative to the center line of CDCl3 (77.0 ppm). Infrared spectra were
recorded on a Perkin–Elmer Infracord spectrophotometer Model 599-B using
sodium chloride optics. Mass spectra were recorded on a Perkin–Elmer Q-
Mass 910 Mass spectrometer. Melting points were determined on a
Thermonik Campbell melting point apparatus and are uncorrected.
Microanalyses were performed on a Carlo-Erba CHNS-O 1108 elemental
analyzer. Dichloromethane was distilled over P2O5 under argon and pyridine
was distilled over KOH under argon. Silica gel (SD’s 60–120 mesh) was used
for column chromatography.
N-Methoxycarbonyl-N-phenoxycarbonyl methylamine (2a). Yield:
1
35%; colourless oil; H NMR (CDCl3): d3.40 (3H, s, NCH3), 3.85 (3H, s,
OCH3), 7.15–7.45 (5H, m, Ar); 13C NMR: d633.54, 53.73, 121.27, 125.78,
129.21, 150.59, 151.93, 153.85; IR (neat): 1760, 1700, 1590, 1490,
1450 cm21; MS (m/z, %): 209 (Mþ, 0.66), 116 (10), 39 (100); Anal. Calcd.
for C10H11NO4: C, 57.41; H, 5.30; Found: C, 57.82; H, 5.20%.
N-(4-Chlorophenoxycarbonyl)-N-methoxycarbonyl methylamine (2b).
Yield: 46%; mp 678C; 1H NMR (CDCl3): d3.35 (311, s, NCH3), 3.85 (3H, s,
OCH3), 7.11 (2H, d, J ¼ 8.8 Hz, Ar), 7.36 (2H, d, J ¼ 8.8 Hz, Ar); 13C NMR:
d33.84, 54.15, 122.87, 129.46, 131.41, 149.12, 151.99, 155.26; IR (nujol):
2900, 1750, 1720, 1440 cm21; (m/z, %): 243 (Mþ, 2), 116 (16), 18 (100);
Anal. Calcd. for C10H10ClNO4: C, 49.30; H, 4.14; N, 5.75; Found: C, 49.55;
H, 4.22; N, 5.66%.
N-(4-Bromophenoxycarbonyl)-N-methoxycarbonyl methylamine (2c).
Yield: 58%; mp 79–808C; 1H NMR (CDCl3): d 3.35 (3H, s, NCH3), 3.90 (3H,
s, OCH3), 7.05 (2H, d, J ¼ 9 Hz, Ar), 7.50 (2H, d, J ¼ 9 Hz, Ar); 13C NMR:
d 33.79, 54.05, 119.02, 123.17, 132.36, 149.63, 151.77, 153.87; IR (nujol):
2900, 1750, 1720, 1440 cm21; MS (m/z, %): 288 (Mþ, 4), 116 (56), 59 (100);
Anal. Calcd. for C10H10BrNO4: C, 41.69; 11, 3.50; N, 4.86; Found: C, 41.80;
11, 3.55; N, 4.70%.
N-Methoxycarbonyl-N-(4-nitrophenoxycarbonyl) methylamine (2d).
1
Yield: 30%; mp 758C; H NMR (CDCl3): d 3.40 (3H, s, NCH3), 3.90 (3H, s,
OCH3), 7.35 (2H, d, J ¼ 9.3 Hz, Ar), 8.30 (2H, d, J ¼ 9.3 Hz, Ar); 13C NMR:
d 33.80, 54.15, 122.27, 125.03, 145.31, 151.05, 153.54, 155.12; IR (nujol):
2900, 1760, 1730, 1440, 1340 cm21; MS (m/z, %): 122 (Mþ 2132, 0.66), 116
(8.5), 30 (100); Anal. Calcd. for C10H10N2O6: C, 47.25; 11,3.97; N, 11.02;
Found: C, 47.16; 11,3.89; N, 10.75%.
N-Methoxycarbonyl-N-(4-methylphenoxycarbonyl) methylamine (2e).
1
Yield: 32%; mp 588C; H NMR (CDCl3): d 2.40 (3H, s, ArCH3), 3.40 (3H,
s,NCH3), 3.90 (3H, s, OCH3), 7.04 (2H, d, J ¼ 8.6 Hz, Ar), 7.18 (2H, d,
J ¼ 8.6 Hz, Ar); 13C NMR: d20.52, 33.54, 53.75, 120.90, 129.67, 135.38,
148.36, 152.15, 153.95; IR (nujol): 2900, 1760, 1720, 1460 cm21; MS (m/z,

38
Joshi, Patkar, and Rajappa
%): 223 (Mþ, 5), 116 (10), 18 (100); Anal. Calcd. for C11H13NO4: C, 59.19;
11, 5.83; N, 6.27; Found: C, 59.19; 11, 6.00; N, 6.08%.
N-Benzyloxycarbonyl-N-methoxycarbonyl methylamine (4). Yield:
1
33%; colourless oil; H VNMR (CDCl3): d 3.25 (3H, s, NCH3), 3.84 (3H, s,
OCH3), 5.25 (2H, s, CH2), 7.30–7.45 (5H, m, Ar); 13C NMR: d 32.97, 53.30,
67.98, 127.56, 127.87, 128.14, 135.31, 153.10, 153.79; IR (neat): 2900, 1760,
1700, 1300 cm21; MS (m/z, %): 224 (Mþ þ 1, 0.15), 107 (0.35), 91 (100);
Anal. Calcd. for C11H13NO4: C, 59.19; 11, 5.83; N, 6.28; Found: C, 59.02; 11,
6.28; N, 6.49%.
ACKNOWLEDGMENTS
We thank CSIR for financial support (to SR) under the Emeritus Scientist
Scheme and for the grant of a Research Associateship (to LNP) and an SRF (to
UMJ). We are thankful to Mrs. Puranik of NCL for the X-ray structure
determination of compound (2c). We thank Ubichem, UK and Excel Ind.,
India for generous gifts of triphosgene.
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Received in the USA July 15, 2003