Pil Ja Seo

Total synthesis of a demethoxy-egonol fromStyrax obassia

The total synthesis of a demethoxy-egonol isolated fromStyrax obassia, 5-(3-hydroxypropyl)-2-(3′,4′-methylenedioxyphenyl)benzofuran (9), is described. The key steps involve the construction of a 2-arylbenzofuran skeleton7 from methyl 3-(4-hydroxyphenyl)propionate with 2-chloro-2-methylthio-(3′,4′-methylenedioxy)acetophenone (6) in the presence of ZnCl2 and successive desulfurization of the resulting product7.

2,5-Dimethyl-3-phenyl­sulfonyl-1-benzofuran

The title compound, C16H14O3S, was prepared by the oxidation of 2,5-dimethyl-3-phenylsulfanyl-1-benzofuran with 3-chloroperoxybenzoic acid. The phenyl ring makes a dihedral angle of 76.98 (9)° with the plane of the benzofuran fragment. The crystal structure is stabilized by π–π interactions between furan and benzene rings of neighbouring molecules [centroid–centroid distance = 3.775 (4) Å]. In addition, the crystal structure exhibits intra- and intermolecular C—H⋯O interactions.

2,5,7-Trimethyl-3-phenyl-sulfinyl-1-benzo-furan.

The title compound, C17H16O3S, was prepared by the oxidation of 2,5,7-trimethyl-3-phenylsulfanyl-1-benzofuran with 3-chloroperoxybenzoic acid. The phenyl ring exhibits a dihedral angle of 81.16 (4)° with the plane of the benzofuran fragment. The crystal structure is stabilized by π–π interactions between the furan and benzene rings of neighbouring molecules [centroid–centroid distance = 3.874 (2) Å] and by C—H⋯π interactions between a phenyl H atom of the phenylsulfonyl substituent and the furan ring of adjacent molecules. In addition, the crystal structure exhibits intra- and intermolecular C—H⋯O interactions.

5-Cyclo-hexyl-2-(4-fluoro-phen-yl)-3-methyl-sulfinyl-1-benzofuran.

In the title compound, C21H21FO2S, the cyclohexyl ring adopts a classic chair conformation. The 4-fluorophenyl ring makes a dihedral angle of 31.05 (6)° with the mean plane of the benzofuran fragment. In the crystal, molecules are linked through weak intermolecular C—H⋯O and C—H⋯π interactions.

5-Bromo-3-ethyl­sulfinyl-2-(4-fluoro­phenyl)-1-benzofuran

In the title compound, C16H12BrFO2S, the 4-fluorophenyl ring is rotated out of the benzofuran plane, as indicated by the dihedral angle of 5.94 (5)°. The crystal structure exhibits aromatic π–π interactions between the benzene ring and the 4-fluorophenyl ring of an adjacent molecule [centroid–centroid distance = 3.632 (2) Å], and a Br⋯O halogen bond with a Br⋯O distance of 3.101 (1) Å.

5-Fluoro-2-(4-fluoro-phen-yl)-3-methyl-sulfinyl-1-benzofuran.

In the title compound, C15H10F2O2S, the O atom and the methyl group of the methylsulfinyl substituent lie on opposite sides of the plane through the benzofuran fragment. The 4-fluorophenyl ring is rotated out of the benzofuran plane by a dihedral angle of 28.09 (3)°. The crystal structure is stabilized by weak intermolecular C—H⋯O and C—H⋯F hydrogen bonds.

3-(4-Fluoro­phenyl­sulfin­yl)-2,5-dimethyl-1-benzofuran

In the title compound, C16H13FO2S, the O atom and the 4-fluorophenyl group of the 4-fluorophenylsulfinyl substituent are located on opposite sides of the plane through the benzofuran fragment; the 4-fluorophenyl ring is nearly perpendicular to this plane, making a dihedral angle of 87.41 (3). The crystal structure exhibits a weak intermolecular C—H⋯O hydrogen bond.

5-Chloro-2-(4-fluoro­phen­yl)-3-phenyl­sulfinyl-1-benzofuran

In the title compound, C20H12ClFO2S, the O atom and the phenyl ring of the phenylsulfinyl substituent lie on opposite sides of the plane of the benzofuran fragment; the phenyl ring is almost perpendicular to this plane [82.44 (5)°]. The 4-fluorophenyl ring is rotated out of the benzofuran plane, making a dihedral angle of 20.83 (6)°.

5-Bromo-3-cyclopentylsulfinyl-2,7-dimethyl-1-benzofuran

In the title compound, C16H19BrO2S, the cyclohexyl ring adopts a chair conformation. In the crystal, molecules are linked by a Br⋯Br [3.5994 (5) Å] contact and a C—H⋯π interaction involving the phenyl ring of the benzofuran. The crystal structure also exhibits a slipped π–π interaction between the furan rings of neighbouring molecules [centroid–centroid distance = 3.767 (1) Å and interplanar distance of 3.452 (1) Å with a slippage of 1.508 Å].

5-Chloro-3-ethyl­sulfinyl-2-(4-fluoro­phen­yl)-1-benzofuran

The asymmetric unit of the title compound, C16H12ClFO2S, contains two independent molecules in which the benzofuran ring systems are essentially planar, with r.m.s. deviations of 0.007 (1) and 0.013 (1) Å. In the crystal, molecules are linked by weak C—H⋯O hydrogen bonds into chains extending along the b axis. These chains are further packed into stacks along the c -axis by S⋯O contacts [3.1898 (11) and 3.1361 (11) Å] involving the sulfinyl groups. In both 3-fluorophenyl rings, the F atom is disordered over two positions, with site-occupancy factors of 0.921 (2) and 0.079 (2).