Download PDF
Synlett 2011(4): 529-534  
DOI: 10.1055/s-0030-1259530
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Simple and Regioselective Synthesis of Dihydropyrido[2,3-c]carbazoles via Iodocyclization

Rama Raju Jella, Rajagopal Nagarajan*
School of Chemistry, University of Hyderabad, Hyderabad 500046, India
Fax: +91(40)23012460; e-Mail: rnsc@uohyd.ernet.in;
Further Information

Publication History

Received 29 November 2010
Publication Date:
08 February 2011 (online)

    Permissions and Reprints All articles of this category

Abstract

An efficient and simple method for the synthesis of various iodo-substituted dihydropyridocarbazole derivatives has been developed via iodocyclization of N-propargylated 3-aminocarbazoles.

Key words

iodocyclization - 3-aminocarbazole - dihydropyridocarbazole

12

The CCDC deposition number for compound 6a is 800159. Formula: C30H25IN2O2S. Unit cell parameters: a = 9.8829 (15), b = 10.3179 (13), c = 14.554 (2), α = 80.103 (11), β = 72.103 (13), γ = 68.283 (13), space group P-1. The CCDC deposition number for compound 7a is 800160. Formula: C23H17IN2. Unit cell parameters: a = 11.4798 (19), b = 10.4089 (15), c = 15.3963 (18), α = 90.00, β = 91.647 (12), γ = 90.00, space group P-1.

13

Preparation of 7-Ethyl-2-iodo-(4-methylphenylsulfonyl)-1-phenyl-4,7-dihydro-3 H -pyrido[2,3- c ]carbazole (6a) To a mixture of 9-ethyl-3-[4-methylphenyl(3-phenylpropyl)-
sulfonamido]-9H-carbazole (5a, 0.5 g, 1 mmol), iodine (0.8 g, 3 mmol), and NaHCO3 (0.36 g, 2 mmol) was added MeCN (20 mL) at r.t. The reaction mixture was stirred for 4 h. The reaction mixture was then diluted with EtOAc, washed with sat. aq Na2S2O3 (20 mL). The organic layer was separated, and the aqueous layer was extracted with EtOAc (25 mL). The combined organic layers were dried over Na2CO3, filtered, and concentrated under the reduced pressure. Product was purified by column chromatography on silica gel (eluent: hexane-EtOAc) afforded 6a (0.48 g, 80%).
Mp 172-174 ˚C. IR (KBr): 3043, 2976, 2926, 1608, 1593, 1440, 1346, 1163, 1087, 883 cm-¹. ¹H NMR (400 MHz, TMS, CDCl3): δ = 8.16 (1 H, d, J = 8.8 Hz, ArCH), 7.55 (4 H, d, J = 7.2 Hz, ArCH), 7.26-7.16 (4 H, m, ArCH), 7.08 (2 H, m, ArCH), 6.95-6.93 (2 H, m, ArCH), 6.60-6.57 (2 H, m, ArCH), 5.00 (2 H, br s, CH2), 2.15 (3 H, s, CH3), 1.44 (3 H, t, J = 6.8 Hz, CH3). ¹³C NMR (100 MHz, TMS, CDCl3): δ = 143.5, 141.0, 140.0, 139.8, 139.4, 135.6, 130.6, 129.9, 129.2, 128.1, 127.7, 127.1, 126.1, 125.2, 124.2, 124.0, 121.8, 118.4, 118.3, 109.2, 107.9, 91.7 (arom. C), 59.8, 37.5, 21.3, 13.6 (aliph. C). MS (positive mode): m/z = 604 [M + H]. Anal. Calcd (%) for C30H25IN2O2S: C, 59.61; H, 4.17; N, 4.63. Found: C, 59.58; H, 4.10; N, 4.56.

14

Preparation of 7-Ethyl-2-iodo-1-phenyl-7 H -pyrido[2,3- c ]carbazole (7a) In a round-bottom flask equipped with a magnetic stirring bar, 7-ethyl-2-iodo-(4-methylphenylsulfonyl)-1-phenyl-4,7-dihydro-3H-pyrido[2,3-c]carbazole (6a, 0.5 mmol) was dissolved in a mixture of THF (20 mL) and MeOH (10 mL) at r.t. Cs2CO3 (1.5 mmol) was added to the clear solution. The resulting mixture was stirred at 50 ˚C, and the progress of the reaction was monitored. When the reaction was complete (12 h), the mixture was evapourated under vacuum. To the residue was added H2O (20 mL), and the mixture was stirred at r.t. for 10 min. Then the aqueous layer was extracted with EtOAc (3 × 20 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure. Product was purified by column chromatography on silica gel (eluent: hexane-EtOAc) afforded 7a (0.2 g, 60%).
Mp 178-180 ˚C. IR (KBr): 3126, 3055, 2972, 1614, 1591, 1504, 1444, 1379, 1253, 952 cm-¹. ¹H NMR (400 MHz, TMS, CDCl3): δ = 9.27 (1 H, s, ArCH), 8.21 (1 H, d, J = 8.0 Hz, ArCH), 7.95 (1 H, d, J = 8.0 Hz, ArCH), 7.58-7.40 (6 H, m, ArCH), 7.27 (1 H, t, J = 8.0 Hz, ArCH), 6.64 (1 H, t, J = 8.0 Hz, ArCH), 5.78 (1 H, d, J = 8.0 Hz, ArCH), 4.5
(2 H, q, J = 8.0 Hz, CH2), 1.48 (3 H, t, J = 4.0 Hz, CH3). ¹³C NMR (100 MHz, TMS, CDCl3): δ = 153.2, 148.4, 145.5, 144.6, 138.8, 138.7, 131.2, 129.4, 129.0, 128.9, 125.8, 124.6, 124.1, 123.4, 118.9, 114.5, 114.1, 108.2, 100.1 (arom. C), 37.6, 14.1 (aliph. C). MS (positive mode): m/z = 449
[M + H]. Anal. Calcd (%) for C23H17IN2: C, 61.62; H, 3.82; N, 6.25. Found: C, 61.31; H, 3.78; N, 6.31.