Novel synthetic method for N-allylcarbamates from allyl ethers using chlorosulfonyl isocyanate

Article abstract of DOI:10.1016/S0040-4039(00)00776-0

Various allyl ethers were converted into the corresponding N- allylcarbamates using chlorosulfonyl isocyanate (CSI) via the stable allylic carbocation rather than β-lactam through [2+2] cycloaddition. The reaction of cinnamyl methyl ether with CSI afforded only methyl N-cinnamylcarbamate at 0°C, but at 20°C, it produced a mixture of methyl N-cinnamylcarbamate and methyl N-(l-phenylprop-2-enyl)carbamate in a 2.7:1 ratio. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00776-0

Tetrahedron Letters 41 (2000) 5073±5076
Novel synthetic method for N-allylcarbamates from allyl
ethers using chlorosulfonyl isocyanate
Ji Deuk Kim, Min Hee Lee, Min Jung Lee and Young Hoon Jung*
College of Pharmacy, Sungkyunkwan University, Suwon 440-746, South Korea
Received 16 March 2000; revised 19 April 2000; accepted 12 May 2000
Abstract
Various allyl ethers were converted into the corresponding N-allylcarbamates using chlorosulfonyl iso-
cyanate (CSI) via the stable allylic carbocation rather than b-lactam through [2+2] cycloaddition. The
reaction of cinnamyl methyl ether with CSI a€orded only methyl N-cinnamylcarbamate at 0ꢀC, but at
20ꢀC, it produced a mixture of methyl N-cinnamylcarbamate and methyl N-(1-phenylprop-2-enyl)carbamate
in a 2.7:1 ratio. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: chlorosulfonyl isocyanate; allyl ether; N-allylcarbamate.
To date, chlorosulfonyl isocyanate (CSI) has been used in the [2+2] cycloaddition reactions of
various substituted alkenes, especially enol ethers, to synthesize the b-lactam moiety of carbapenem
antibiotics and b-amino acids.1 7 Recently, chiral enol ethers have been used as the precursors of
chiral b-lactam compounds and chiral b-amino acids.8,9 As part of a program aimed at producing
various amino acids which can be used as a versatile building block, benzyl allyl ether was reacted
with CSI to obtain a b-lactam with a benzyloxy methyl moiety, which can be readily converted to
the acid moiety. However, rather than obtaining the b-lactam, we unexpectedly obtained the
corresponding carbamate.10 Speci®cally, instead of obtaining the expected b-lactam products
arising from formal [2+2] annulation, the corresponding N-allylcarbamates were obtained as sole
products (Scheme 1). Early examples of N-allylcarbamate formation using CSI were reported by
several groups, in which the reactions of unsaturated oxiranes or acetal moieties in sugars with
CSI were studied.11,12 Similar results of the conversion of tertiary or allyl alcohols to the corre-
sponding amines using CSI were also reported.13,14
However, no further systematic studies on these reactions have been performed. Therefore, we
investigated this novel reaction by varying solvents and temperatures to optimize the yield; the
results are summarized in Table 1.
* Corresponding author. E-mail: yhjung@skku.ac.kr
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00776-0

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Scheme 1.
Table 1
Results of the reactions of cinnamyl methyl ether (1) and CSI conducted with di€erent solvents and temperatures
From these results, the best condition was determined to involve methylene chloride at 20ꢀC.
Therefore, various allyl ethers were reacted with CSI under these conditions; the results are
shown in Table 2.
The formation of N-allylcarbamates can be rationalized in terms of the abstraction of the
alkoxy moiety by CSI to give the ClSO2±N^±CO2CH3 species and the stable allylic carbocation.
Nitrogen species may attack C(1) by avoiding steric hindrance of the phenyl ring or the dimethyl
moiety (entries 1±9 and 12). In the case of entry 11, a 1:1 mixture of the terminal and internal
carbamate was obtained due to the reduced steric hindrance.

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Table 2
Conversions of allyl ethers to the corresponding N-allylcarbamates with CSIa
A typical preparatory procedure is as follows: To a solution of Na2CO3 (2.25 equiv.) in anhydrous
methylene chloride (7 mL) was added CSI (1.5 equiv.) and a solution of cinnamyl methyl ether
(350 mg, 2.36 mmol) in methylene chloride (3 mL) at 20ꢀC. The reaction mixture was stirred for
0.5 h at 20ꢀC, quenched with H2O, then extracted with ethyl acetate (10 mL). The organic layer

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was added to a solution of Na2SO3 (25%) and KOH (10%) and the reaction mixture was stirred
overnight at 20ꢀC. It was then extracted with ethyl acetate, and after the usual work-up, column
chromatography a€orded 3 (288 mg, 63.8%) and 4 (107 mg, 23.7%).
Compound 3: 1H NMR (500 MHz, CDCl3): 3.70 (s, 3H), 3.96±3.98 (t, 2H, J=5 Hz), 4.89±4.97
(br, 1H), 6.17±6.22 (m, 1H), 6.50±6.53 (d, 1H, J=15.5 Hz), 7.22±7.37 (m, 5H). Compound 4: 1H
NMR (500 MHz, CDCl3): 3.69 (s, 3H), 5.00±5.10 (br, 1H), 5.22±5.26 (m, 2H), 5.30±5.38 (br, 1H),
5.97±6.04 (m, 1H), 7.26±7.36 (m, 5H).
In conclusion, CSI was found to react with allyl ethers at room temperature in methylene
chloride to give the corresponding N-allylcarbamates via the stable allylic carbocation. We are
actively pursuing further applications of this interesting reaction, including a more re®ned de®nition
of its reaction mechanism with an eye toward regioselectivity due to preference between cationic
stability and steric hindrance.
Acknowledgements
The authors wish to acknowledge the ®nancial support of the Korea Research Foundation
made in the program year of 1998.
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