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Synlett 2007(17): 2733-2737  
DOI: 10.1055/s-2007-991071
LETTER
© Georg Thieme Verlag Stuttgart · New York

Electrocyclization Reactions of Annulated 1,2-Diazahepta-2,4-dien-6-ynyl Anions

Volodymyr Lyaskovskyy, Roland Fröhlich, Ernst-Ulrich Würthwein*
Organisch Chemisches Institut, Westfälische Wilhelms-Universität and International NRW Graduate School of Chemistry, Münster, Corrensstraße 40, 48149 Münster, Germany
Fax: +49(251)8339772; e-Mail: wurthwe@uni-muenster.de;
Further Information

Publication History

Received 10 July 2007
Publication Date:
25 September 2007 (online)

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Abstract

Hydrazones 12a,b,f furnish annulated indenone derivatives (6-azafulvenes) 13a-d upon deprotonation with t-BuOK in DMF at 50 °C. In contrast, deprotonation of a similar N-methyl ­hydrazone 12d unexpectedly leads to the isoquinoline derivative 15. Mechanisms for both transformations are proposed, supported by quantum chemical density functional theory (DFT) and ab initio calculations.

Key words

anionic electrocyclic reactions - indenes - heterocycles - hydrazones - quinolines - 6-azafulvenes

    References and Notes

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7

Preparation of 1-[2-(Hex-1-ynyl)benzylidene]-2-phenyl-hydrazine (12a): A mixture of 2-(1-hexynyl)benz-aldehyde (0.93 g, 5.00 mmol) and phenylhydrazine (0.54 g, 5.00 mmol) in anhyd CH2Cl2 (20 mL) was stirred in the presence of molecular sieves (4 Å) at r.t. for 16 h. Molecular sieves were removed by filtration through Celite and washed with CH2Cl2 (20 mL). The solvent was removed in vacuo to afford the hydrazone 12a (1.10 g, 4.00 mmol, 80%) as a yellow oil. The obtained hydrazone was pure enough to be used without further purification. FTIR (film): 3313 (br, w), 2931 (s), 2871 (s), 2862 (m), 2225 (m), 1575 (m), 1494 (s), 1448 (m), 1257 (s), 1145 (m) cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.98 (t, J = 7.3 Hz, 3 H), 1.47-1.68 (m, 4 H), 2.48 (t, J = 7.4 Hz, 2 H), 6.87 (tt, J = 7.3, 1.2 Hz, 1 H), 7.11-7.14 (m, 2 H), 7.19 (dd, J = 7.4, 1.4 Hz, 1 H), 7.25-7.30 (m, 3 H), 7.38 (dm, J = 7.8 Hz, 1 H), 7.72 (br s, 1 H, NH), 8.04 (dm, J = 8.0 Hz, 1 H), 8.19 (s, 1 H, CH=N). 13C NMR (100 MHz, CDCl3): δ = 13.7, 19.4, 22.2, 30.9, 78.1, 95.7, 112.8, 120.2, 122.4, 124.5, 127.8, 127.9, 129.3, 132.6, 136.0, 136.1, 144.6. HRMS (ESI): m/z calcd for C19H20N2H: 277.1705; found: 277.1699. Anal. Calcd for C19H20N2: C, 82.57; H, 7.29; N, 10.14. Found: C, 82.87; H, 7.48; N, 9.57.

8

Preparation of 1-(2-Butyl-1 H -inden-1-ylidene)-2-phenylhydrazine (13a): Hydrazone 12a (0.28 g, 1.00 mmol) was added under argon to the solution of t-BuOK (0.22 g, 2.00 mmol) in DMF (5 mL) and the mixture was stirred at 50 °C until all starting hydrazone had disappeared (approx. 5 h, TLC monitoring). H2O (20 mL) was added and the mixture was extracted with Et2O (3 × 20 mL). The combined organic extracts were dried with MgSO4 and the residue was purified by flash chromatography (Et2O-pentane-Et3N, 0.5:10:0.2) giving 13a (0.07 g, 0.25 mmol, 25%) as a yellowish oil. FTIR (film): 2956 (s), 2927 (s), 1600 (s), 1566 (s), 1504 (s), 1494 (s), 1255 (s), 1207 (s), 1168 (s), 1151 (w), 1122 (m), 1093 (w) cm-1. 1H NMR (500 MHz, CDCl3): δ = 1.00 (t, J = 7.1 Hz, 3 H), 1.43-1.52 (m, 2 H), 1.68-1.75 (m, 2 H), 2.66-2.69 (m, 2 H), 6.56 (s, 1 H), 7.03 (tt, J = 7.3, 1.0 Hz, 1 H), 7.17-7.40 (m, 7 H), 7.68 (d, J = 7.2 Hz, 1 H), 8.92 (s, 1 H). 13C NMR (125 MHz, CDCl3): δ = 14.1, 22.7, 26.2, 31.4, 113.6, 121.0, 121.8, 122.7, 124.9, 126.1, 127.4, 128.8, 129.4, 143.9, 144.0, 144.1, 144.3. HRMS (ESI): m/z calcd for C19H20N2H: 277.1705; found: 277.1699. Anal. Calcd for C19H20N2: C, 82.57; H, 7.29; N, 10.14. Found: C, 82.64; H, 7.54; N, 9.62.

9

CCDC 658782 contains the supplementary crystallographic data of picrate 13d·2,4,6-(O 2 N) 3 C 6 H 2 ( OH). These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(1223)336033, E-mail: deposit@ccdc.cam.ac.uk].

10

Preparation of 3-Butylisoquinoline (15): Hydrazone 12d (0.21 g, 1.00 mmol) was added under argon to the solution of t-BuOK (0.22 g, 2.00 mmol) in DMF (5 mL) and the mixture was stirred at r.t. until all starting hydrazone had disappeared (approx. 0.5 h, TLC monitoring). H2O (20 mL) was added and the mixture was extracted with Et2O (3 × 20 mL). The combined organic extracts were dried with MgSO4 and the residue was purified by flash chromatography (tert-butyl methyl ether) giving 15 (0.09 g, 0.47 mmol, 47%) as a yellow oil. All spectroscopic and physical data were in accordance with published data (see ref. 11).