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DOI: 10.1055/s-2004-822907
Cyclisation of Unsaturated N-Chloroamines under Acidic Conditions: A Polar Reaction via Chloronium Ions
Publikationsverlauf
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.
Key words
cyclisation - heterocycles - addition reactions - aminations
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References
We have performed the reaction in deuterated acetic acid and detected the intermediate by NMR.
9Reaction 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.
10In the proposed radical-type cyclisations of chloroamines by Somfai, borontrifluoride etherate was found to be the superior Lewis acid too (see ref. 3).