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Synlett 2011(11): 1515-1518  
DOI: 10.1055/s-0030-1260769
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Efficient Brønsted Acid Catalyzed Hydrations and Hydroaminations of (Dicyclopropylmethylene)cyclopropane

Lutz Ackermann*a, Sergei I. Kozhushkova, Dmitry S. Yufitb, Ilan Marekc
a Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
Fax: +49(551)396777; e-Mail: lutz.ackermann@chemie.uni-goettingen.de;
b Department of Chemistry, University of Durham, Durham, South Rd., DH1 3LE, UK
c Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
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Publication History

Received 28 February 2011
Publication Date:
01 June 2011 (online)

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Abstract

(Dicyclopropylmethylene)cyclopropane underwent efficient Brønsted acid catalyzed hydrations and hydroaminations with H2O and basic amines, respectively, occurring with conservation of all three cyclopropane rings.

Key words

Brønsted acids - catalysis - hydroaminations - methy­lenecyclopropanes - ring conservation

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However, traces (<5%) of a ring-opened product were detected in the ¹H NMR spectrum of crude product 7b.

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General Procedure for the Preparation of Benzyl(tricyclopropylmethyl)amine (7a), Phenethyl(tricyclopropylmethyl)amine (7b) and n -Octyl(tricyclopropylmethyl)amine (7c): A flame-dried Schlenk flask was cooled and charged with 1, (402.6 mg, 442.1 µL, 3.0 mmol), the corresponding amine (1.0 equiv) and NH4Cl (16.0 mg, 10 mol%) in anhyd 1,4-dioxane (3.0 mL) under Ar. After stirring the reaction mixture for 48 h at 120 ˚C, Et2O (50 mL) was added at ambient temperature, and the reaction mixture was extracted with aq HCl (0.1 N, 2 × 80 mL). The combined aqueous phases were washed with Et2O (2 × 50 mL) and, after addition of aq NaOH (1 N, 25 mL), extracted with CH2Cl2 (3 × 40 mL). The combined organic phases were dried over K2CO3 and concentrated under reduced pressure. The residue was dissolved in MeOH (20 mL), stirred with charcoal (2.0 g) at ambient temperature overnight, quickly filtered through a thin pad of silica gel and concentrated in vacuo. Amines 7a-c (1.0 mmol) were dissolved in CH2Cl2 (5.0 mL), and a solution of p-TsOH˙H2O (190.2 mg, 1.0 mmol, 1.0 equiv) in MeOH (2.0 mL) was added in one portion at ambient temperature. After an additional stirring for 10 min, the reaction mixture was evaporated, and the corresponding p-toluenesulfonate was purified by slow evaporation of its solution in CH2Cl2-octane (7a˙p-TsOH: 92% yield, and 7c˙p-TsOH: 94% yield) or in THF-octane (7b˙p-TsOH: 95% yield) at +4 ˚C. Compound 7a: colorless oil. ¹H NMR (250 MHz, CDCl3):
δ = 7.21-7.38 (m, 5 H), 3.98 (s, 2 H), 1.53 (br s, 1 H), 0.69-0.71 (m, 3 H), 0.48-0.53 (m, 6 H), 0.29-0.35 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 142.3 (C), 128.0 (CH), 127.8 (CH), 126.6 (CH), 52.9 (C), 46.7 (CH2), 15.9 (CH), 0.0 (CH2). Compound 7a×p-TsOH: colorless crystals; mp 137-139 ˚C. ¹H NMR (250 MHz, CDCl3): δ = 8.34 (br s, 2 H), 7.65 (d, J = 8.0 Hz, 2 H), 7.52-7.56 (m, 2 H), 7.20-7.26 (m, 3 H), 7.16 (d, J = 8.0 Hz, 2 H), 4.29 (t, J = 5.6 Hz, 2 H), 2.37 (s, 3 H), 0.65-0.75 (m, 9 H), 0.40-0.47 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 142.4 (C), 139.9 (C), 132.4 (C), 130.2 (CH), 128.6 (CH), 128.5 (CH), 128.4 (CH), 125.9 (CH), 67.0 (C), 46.5 (CH2), 21.3 (Me), 11.5 (CH), 1.8 (CH2). Compound 7b: colorless oil. ¹H NMR (250 MHz, CDCl3): δ = 7.17-7.29 (m, 5 H), 3.05 (t, J = 7.3 Hz, 2 H), 2.75 (t, J = 7.3 Hz, 2 H), 1.53 (br s, 1 H), 0.51-0.60 (m, 3 H), 0.36-0.42 (m, 6 H), 0.20-0.32 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 140.6 (C), 128.7 (CH), 128.1 (CH), 125.8 (CH), 52.9 (C), 43.8 (CH2), 37.5 (CH2), 15.6 (CH), 0.0 (CH2). Compound 7b˙p-TsOH: colorless crystals; mp 149-150 ˚C. ¹H NMR (250 MHz, CDCl3): δ = 8.48 (br s, 2 H), 7.80 (d, J = 8.0 Hz, 2 H), 7.12-7.26 (m, 7 H), 3.25-3.41 (m, 4 H), 2.38 (s, 3 H), 0.72-0.75 (m, 9 H), 0.41-0.46 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 142.8 (C), 140.0 (C), 137.8 (C), 129.0 (CH), 128.8 (CH), 128.5 (CH), 126.6 (CH), 125.8 (CH), 65.2 (C), 43.9 (CH2), 32.7 (CH2), 21.3 (Me), 11.0 (CH), 1.4 (CH2). Compound 7c: colorless oil. ¹H NMR (250 MHz, CDCl3): δ = 2.75 (t, J = 7.0 Hz, 2 H), 1.65 (br s, 1 H), 1.35-1.51 (m, 2 H), 1.27 (m, 10 H), 0.88 (t, J = 6.5 Hz, 3 H), 0.54-0.63 (m, 3 H), 0.37-0.45 (m, 6 H), 0.23-0.30 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 42.4 (C), 31.8 (CH2), 31.4 (CH2), 29.6 (CH2), 29.3 (CH2), 27.5 (CH2), 26.4 (CH2), 22.6 (CH2), 15.7 (CH), 14.1 (Me), 0.0 (CH2). Compound 7c˙p-TsOH: colorless crystals; mp 159-161 ˚C. ¹H NMR (250 MHz, CDCl3): δ = 8.18 (br s, 2 H), 7.71 (d, J = 8.3 Hz, 2 H), 7.14 (d, J = 8.3 Hz, 2 H), 3.03 (m, 2 H), 2.35 (s, 3 H), 1.92 (m, 2 H), 1.22 (m, 10 H), 0.88 (t, J = 6.5 Hz, 3 H), 0.73-0.75 (m, 9 H), 0.42-0.50 (m, 6 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 143.0 (C), 139.6 (C), 128.6 (CH), 125.7 (CH), 64.8 (C), 42.3 (CH2), 31.8 (CH2), 29.4 (CH2), 29.2 (CH2), 27.4 (CH2), 26.4 (CH2), 22.6 (CH2), 21.3 (Me), 14.1 (Me), 11.0 (CH), 1.4 (CH2).

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CCDC 821336 (7a˙p-TsOH), CCDC 821337 (7b˙p-TsOH) and CCDC 821338 (7c˙p-TsOH) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK; fax: +44 (1223)336033; or deposit@ccdc.cam.ac.uk].