Synlett 2004(6): 1110-1112  
DOI: 10.1055/s-2004-822907
LETTER
© Georg Thieme Verlag Stuttgart · New York

Cyclisation of Unsaturated N-Chloroamines under Acidic Conditions: A Polar Reaction via Chloronium Ions

Michael Noack, Stefanie Kalsow, Richard Göttlich*
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstr. 40, 48149 Münster, Germany
e-Mail: gottlir@uni-muenster.de;
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Publikationsverlauf

Received 15 January 2004
Publikationsdatum:
08. April 2004 (online)

Abstract

Unsaturated N-chloroamines cyclise under acidic conditions without addition of a starter for a radical reaction. Therefore it can be concluded that, under the conditions published to date in the literature, the reaction at least partially proceeds via a polar reaction mechanism rather than via free radicals.

6

We have performed the reaction in deuterated acetic acid and detected the intermediate by NMR.

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Reaction conditions: To a solution of 2 mmol chloroamine in 5 mL CH2Cl2 4 mmol BF3·ΟEt2 was added at -78 °C and the reaction stirred at this temperature for 1 h. Then 10 mL aq KOH (10%) was added and the mixture was allowed to warm to r.t. The organic phase was separated and the aquous layer washed twice with 10 mL CH2Cl2 each. The combined organic layers were dried over Na2SO4, the solvent removed in vacuo and the product obtained from the residue by flash-chromatography. NMR-data of 2a (d 6-benzene): 1H NMR (300 MHz): δ = 0.90 (s, 3 H), 0.91 (t, 3 H, J = 7.1 Hz), 1.06 (s, 3 H), 1.18-1.45 (m, 4 H), 1.50 (dd, 1 H, J = 12.6 and 6.3 Hz), 1.72 (dd, 1 H, J = 12.6 and 8.7 Hz), 1.91 (d, 1 H, J = 9.0 Hz), 2.08 (m, 1 H), 2.51 (m, 1 H), 2.65 (m, 1 H), 2.73 (d, 1 H, J = 8.4 Hz), 3.21 (dd, 1 H, J = 10.5 and 8.4 Hz), 3.44 (dd, 1 H, J = 10.5 and 3.6 Hz). 13C NMR (75 MHz): δ = 14.1, 20.7, 28.1, 29.5, 31.5, 36.3, 45.0, 47.9, 54.7, 66.4, 68.1. Exact mass spectrometry: C11H22NCl, calcd: 203.14358; found: 203.14426.

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In the proposed radical-type cyclisations of chloroamines by Somfai, borontrifluoride etherate was found to be the superior Lewis acid too (see ref. 3).