R. Sivasakthikumaran

Lewis Acid/Brönsted Acid Mediated Benz-Annulation of Thiophenes and Electron-Rich Arenes

A facile preparation of benz-annulated heterocycles were achieved at rt involving a Lewis acid/Brönsted acid mediated annulation of heterocycles using 2,5-dimethoxytetrahydrofuran as a four-carbon synthon. The benz-/naphth-annulation was found to be successful with electron-rich arenes as well.

Synthesis of annulated arenes and heteroarenes involving Lewis acid-mediated regioselective annulation of unsymmetrical 1,2-(diaryl/diheteroarylmethine)dipivalates.

A ZnBr(2)-mediated regioselective annulation of unsymmetrical 1,2-diarylmethinedipivalates in DCM at room temperature led to the formation of annulated arenes and heteroarenes. The annulation of the dipivalate proceeds through the intermediacy of benzylic carbocations followed by intramolecular cyclization and subsequent aromatization to give the annulated products. The annulation methodology is highly efficient for the syntheses of anthracene as well as naphtho[b]thiophene analogues.

[2-(2-Meth­oxy-1-naphtho­yl)phen­yl](1-naphth­yl)methanone

The title compound, C29H20O3, adopts an ‘S’ conformation with a dihedral angle of 68.5 (2)° beween the two acetone planes. The central phenyl ring forms dihedral angles of 83.8 (4) and 84.5 (4)° with the naphthalene and methoxy-substituted naphthalene mean planes, respectively. Both carbonyl-group O atoms deviate significantly from the naphthalene moiety and the methoxy-substituted naphthalene moiety [0.574 (1) and −1.053 (1) Å, respectively]. The crystal packing is stabilized by C—H⋯O intermolecular interactions, generating C(7) chain and R 2 2(10) graph-set motifs.

(2-Benzoyl­phen­yl)(3,4-dimethyl­phen­yl)methanone

In the title compound, C22H18O2, the central benzene ring forms dihedral angles of 76.0 (1) and 73.1 (1)° with the phenyl ring and dimethyl-substituted benzene ring, respectively. The carbonyl-group O atoms deviate significantly from the phenyl ring and the dimethyl-substituted benzene ring [−0.582 (12) and 0.546 (12) Å, respectively]. The crystal packing is stabilized by C—H⋯π interactions.

[2-(3,4-Dimethyl-benzo-yl)phen-yl](4-meth-oxy-phen-yl)methanone.

The title molecule, C23H20O3, is disordered with a 180° rotation about an axis normal to the length of the molecule, with the major and minor components in a 0.545 (5):0.455 (5) ratio. In the major component, the central benzene ring forms dihedral angles of 72.34 (3) and 69.46 (3)° with the dimethyl-substituted and methoxy-substituted benzene rings, respectively. Moreover, the central benzene ring forms dihedral angles of 50.86 (5) and 58.43 (4)° with the mean planes of the ketone groups. In the minor component, the corresponding dihedral angles between the benzene rings are 71.36 (4) and 67.94 (4)° and the dihedral angles between the benzene ring and the ketone groups are 56.44 (9) and 55.51 (8)°. In the crystal, C—H⋯O interactions generate a C(9) chain along the a-axis direction.

6-Phenyl­benzo[d]naphtho­[2,3-b]thio­phene

In the title compound, C22H14S, the r.m.s. deviation from the mean plane of the four-fused-ring naphthothiophene unit is 0.056 Å. The dihedral angle between the naphthothiophene plane and the pendant phenyl ring is 67.24 (6)°. In the crystal, weak C—H⋯π and π–π stacking [minimum centroid–centroid separation = 3.7466 (10) Å] interactions are observed, which together lead to (010) sheets.

6-(4-Meth-oxy-phen-yl)naphtho[2,3-b][1]benzothio-phene.

The asymmetric unit of the title compound, C23H16OS, contains two independent molecules with opposite orientations of the methoxy groups bonded to the benzene rings. The napthobenzothiophene group in the two molecules is separated by an average distance of 3.912 Å. In both molecules, the napthobenzothiophene unit is almost planar, with r.m.s deviations of 0.0522 and 0.0143 Å. The methoxyphenyl ring makes dihedral angles of 67.0 (6)° and 70.4 (6)° with respect to the napthobenzothiophene ring system in the two molecules. The crystal packing features C—H⋯S, π–π [centroid–centroid distances = 3.666 (10) and 3.658 (10) Å] and C–H⋯π interactions, forming a sheet running along the b-axis direction.

9-(4-Meth-oxy-phen-yl)anthracene.

In the title compound, C21H16O, the dihedral angle between the anthracene ring system and the benzene ring is 74.3 (5)°. The anthracene ring system is essentially planar (r.m.s. deviation = 0.0257 Å) and the methoxy group lies in the plane of the benzene ring [C1—O1—C2—C7 torsion angle = 0.5 (2)°]. The crystal structure features π–π [centroid–centroid distance = 3.9487 (12) Å] and C–H⋯π interactions, forming a sheet running along the a-axis direction.

(2-Benzoyl­phen­yl)(2-meth­oxy-1-naphth­yl)methanone

In the title compound C25H18O3, the central benzene ring forms dihedral angles of 87.4 (5) and 85.4 (4)° with the phenyl ring and the naphthalene ring system, respectively. The carbonyl O atoms deviate significantly from the phenyl ring and the methoxy-substituted naphthalene ring system [by 0.508 (1) and 0.821 (1) Å, respectively]. The crystal packing is stabilized by C—H⋯O hydrogen bonds, which generate C(6) chains, and C—H⋯π interactions.

(2-Benzoyl-phen-yl)(naphthalen-1-yl)methanone.

In the title compound, C24H16O2, the naphthalene ring system makes dihedral angles of 78.5 (6) and 65.5 (7)° with the terminal and central benzene rings, respectively. The dihedral angle between the benzene rings is 74.5 (8)°. In the crystal, neighbouring molecules are interlinked through two C—H⋯π interactions, which construct a two-dimensional supramolecular framework extending infinitely along (010).