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Synlett 2010(1): 97-100  
DOI: 10.1055/s-0029-1218575
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Sequential Catalytic Reactions for the Synthesis of Benzofulvenes Using an Iridium Complex with Dual Function

Kyoji Tsuchikama, Mitsugu Kasagawa, Kohei Endo, Takanori Shibata*
Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, Okubo, Shinjuku, Tokyo, 169-8555, Japan
Fax: +81(3)52868098; e-Mail: tshibata@waseda.jp;
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Publication History

Received 21 October 2009
Publication Date:
11 December 2009 (online)

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Abstract

The cationic iridium complex ([Ir(cod)2]OTf + rac-­BINAP) efficiently catalyzed a sequential process of ortho-C-H bond functionalization, cyclization and dehydration, leading to a concise preparation of 1-methylene indene (benzofulvene) derivatives. The iridium complex operated as a catalyst in the ortho-C-H bond alkenylation of aryl ketones with alkynes and as a Lewis acid catalyst in the cyclization of the alkenylated product and the subsequent dehydration.

Key words

catalysis - cyclization - C-H bond functionalization - ­indenes - iridium

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10

Typical experimental procedure (Table  [¹] , entry 1):
[Ir(cod)2]OTf (10.9 mg, 20 µmol), rac-BINAP (12.6 mg, 20 µmol), and diphenylacetylene (1a; 37.7 mg, 0.21 mmol) were placed in an oven-dried Schlenk tube, which was then evacuated and backfilled with argon (× 3). To the reaction vessel were added 2-methoxyacetophenone (2b; 60.1 mg, 0.40 mmol) and PhCl (0.2 mL, pretreated by argon bubbling for 30 s) before the solution was stirred at 135 ˚C for 24 h. The resultant mixture was cooled to room temperature and filtered through a silica pad. After evaporation of the solvent, the crude products were purified by thin-layer chromatog-raphy (hexane-EtOAc, 10:1) to yield analytically pure product 3ab (62.4 mg, 95%). Yellow solid; mp 95 ˚C. ¹H NMR (400 MHz): δ = 3.98 (s, 3 H), 5.84 (d, J = 1.5 Hz, 1 H), 6.73 (d, J = 1.5 Hz, 1 H), 6.86 (d, J = 8.3 Hz, 1 H), 7.01 (d, J = 7.6 Hz, 1 H), 7.18-7.28 (m, 11 H); ¹³C NMR (100 MHz): δ = 55.3, 109.0, 113.5, 119.8, 121.5, 126.8, 127.2, 127.9, 128.1, 129.0, 129.6, 130.9, 134.6, 134.7, 138.2, 140.7, 144.6, 146.5, 156.2; IR (KBr): 1599, 1442, 1260, 1083, 700 cm-¹; HRMS (FAB+): m/z calcd for C23H18O: 310.1358; found: 310.1351.

12

The geometry was determined by NOESY measurement.