Activation of a water molecule under mild conditions by ruthenacyclopentatriene: mechanism of hydrative cyclization of diynes

Yoshihiko Yamamoto, Ken Yamashita, Hisao Nishiyama
2011 Chemical Communications  
General Considerations: Column chromatography was performed on silica gel (Cica silica gel 60N) or neutral alumina (Merck Aluminum oxide 90 standardized) with mixed solvents. 1 H and 13 C NMR spectra were obtained for samples in CDCl 3 solutions at 25 ˚C. 1 H NMR chemical shifts are reported in terms of chemical shift (δ, ppm) relative to the singlet at 7.26 ppm for chloroform. Splitting patterns are designated as follows: s, singlet; d, doublet; t, triplet; q, quartet; quint, quintet; sext,
more » ... tet; sept, septet; m, multiplet. Coupling constants are reported in Hz. 13 C NMR spectra were fully decoupled and are reported in terms of chemical shift (δ, ppm) relative to the triplet at 77.0 ppm for CDCl 3 . Melting points were obtained in capillary tubes. [Cp*RuCl(cod)] (1), 1 and ruthenacyclopentatriene 3 2 were prepared according to the reports. Diyne 2, 3 ketone 5, 4 and [Cp*RuCl(dppe)] (7) 4 were known compounds. Diphenylphosphinoethane, all silver salts, and solvents were purchaced and used as received. Genral procedure for Reaction of Ruthenacycle 3 with H 2 O. (a) Reaction in the absence of additives: To a vigorously stirred solution of 3 (25.8 mg, 0.0498 mmol) in degassed THF (1.5 mL) was added degassed H 2 O (1.0 mL) under argon atmosphere. The mixture was stirred at 25 ˚C for 4 h. The solution was diluted with 20 mL of THF, dried over K 2 CO 3 , and filtrated. The residue was washed with THF and CHCl 3 (10 mL each). The combined filtrate was concentrated in vacuo to give a mixture of 3, η 5 -oxapentadiene complex 4, ketone 5, and furan 6. Crude yields were determined as unreacted 3 (0.00782 mmol, 16%), 4 (0.0268 mmol, Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2011 54%), 5 (0.00233 mmol, 5%), and 6 (0.00137 mmol, 3%) by 1 H NMR analysis with ethylbenzene (5.0 µL, 0.0410 mmol) as internal standard. (b) Reaction in the presence of a silver salt: To a vigorously stirred solution of AgNO 3 (9.35 mg, 0.0550 mmol) in degassed H 2 O (1.0 mL) was added a solution of 3 (25.9 mg, 0.0500 mmol) in degassed THF (1.5 mL) under Ar atmosphere. The reaction mixture was stirred for 1 h at 25 ˚C. After diluted with THF (20 mL), the solution was dried over K 2 CO 3 , and filtrated. The residue was washed with THF and CHCl 3 (10 mL each). The combined organic layer was concentrated in vacuo to give a mixture of 4 (0.00371 mmol, 7%) and furan 6 ( 0.0261 mmol, 52%) as analyzed by 1 H NMR analysis with ethylbenzene (5.0 mL, 0.0410 mmol) as internal standard. The crude mixture was purified with silica gel column chromatography (elution with hexane/CH 2 Cl 2 1:1 ~ 1:2) to give 6 (6.20 mg, 0.0236 mmol, 47 %) as colorless crystals ( mp. 167.5-169.5 ˚C): 1 H NMR (300 MHz, CDCl 3 ) δ 5.08 (s, 4 H), 7.26 (tt, J = 1.2, 7.4 Hz, 2 H), 7.38-7.44 (m, 4 H), 7.49-7.53 (m, 4 H); 13 C NMR (75 MHz, CDCl 3 ) δ 66.5, 123.6, 126.8, 128.3, 128.7, 130.1, 141.3; HRMS (FAB) m/z calcd for C 18 H 14 O 2 262.0994, found 262.0994 [M] + . (c) Reaction in the presence of neutral alumina: To a solution of 3 (25.9 mg, 0.0500 mmol) in degassed THF (1.5 mL) was added degassed water (1.0 mL) and Al 2 O 3 (64.8 mg, 636 mmol). The reaction mixture was flushed with argon. The mixture was stirred at 25 °C for 4 h. Then the mixture was diluted with THF (20 mL), dried over K 2 CO 3 , and filtrated. The residue was washed with THF and CHCl 3 (10 mL each). The combined solution was concentrated in vacuo. The crude mixture was purified with alumina column chromatography. The yellow band eluted with a mixed solvent (hexane/CHCl 3 1:1 ~ 0:1) was concentrated in vacuo to give 4 (18.
doi:10.1039/c0cc04345a pmid:21116535 fatcat:wtrmhjhoarf7fbzzci4ci6zbgq