Synthesis of the Trans-Syn-Trans Perhydrobenzo[f]chromene Ring System

<p>A stereoselective synthesis of the <i>trans</i>-<i>syn</i>-<i>trans </i>perhydrobenzo[<i>f</i>]chromene skeleton is presented. The target compound <b>3 </b>was achieved in six steps starting from the (<i>S</i>)-(+)-Wieland-Miescher ketone. Key steps include the sp² alkylation at the a-carbon of an unsaturated ketone, Birch-type reductive alkylation, and an acid-catalyzed cyclization. </p>

Synthesis of the Trans-Syn-Trans Perhydrobenzo[f]chromene Ring System

<p>A stereoselective synthesis of the <i>trans</i>-<i>syn</i>-<i>trans </i>perhydrobenzo[<i>f</i>]chromene skeleton is presented. The target compound <b>3 </b>was achieved in six steps starting from the (<i>S</i>)-(+)-Wieland-Miescher ketone. Key steps include the sp² alkylation at the a-carbon of an unsaturated ketone, Birch-type reductive alkylation, and an acid-catalyzed cyclization. </p>

Visible Light Mediated Synthesis of 6H-Benzo[c]chromenes: Transition-Metal-Free Intramolecular Direct C-H Arylation

A synthetic approach towards 6H-benzo[c]chromene ring under visible light and transition-metal-free conditions has been developed. Benzochromenes are synthesized from the corresponding (2-halobenzyl) phenyl ethers or (2-halophenyl) benzyl ethers using KOtBu...

Using Sodium Hydride and Potassium Carbonate as Bases in Synthesis of Substituted 2-Amino-4-aryl-7-propargyloxy-4H-chromene-3-carbonitriles

Aims and Objective: 1-Alkynes are the important precursors for the CuAAC click chemistry. The hybrid of 1,2,3-triazole ring to the chromene ring and sugar moiety could bring some remarkable biological properties. Propargyl derivatives are usually used in the click chemistry. This article reported the synthesis of 2-amino-4-aryl-7-propargyloxy-4-aryl-4H-chromene-3-carbonitriles using propargyl bromide as alkylation agent and the use of potassium carbonate and sodium hydride as bases in the conversion of 2-amino-4-aryl-7- hydroxy-4-aryl-4H-chromene-3-carbonitriles into corresponding propargyl ethers in Williamson’s ether synthesis. Materials and Methods: The use of CTAB for the synthesis of benzylidene malononitriles and anhydrous potassium carbonate as a catalyst in absolute ethanol in the synthesis of 2-amino-7-hydroxy-4H-chromene-3- carbonitriles is an efficient and simple synthetic method. Propargyl ether compounds of these 4H-chromene-3- carbonitriles were obtained from the alkylation reaction by propargyl bromide. Two procedures were applied: K2CO3 as a base in acetone solvent (Procedure A) and NaH as a base in DMF solvent (Procedure B). The single-crystal X-ray structure of propargyl ether 5e has been studied. Results: The use of K2CO3 and NaH as bases in the Williamson’s ether synthesis from 2-amino-7-hydroxy-4Hchromene- 3-carbonitriles showed that Procedure B was the better route and gave ethers in the higher yields. 2- Amino-4-aryl-7-propargyloxy-4-aryl-4H-chromene-3-carbonitriles were obtained from corresponding 7- hydroxy-4H-chromene-3-carbonitriles. Yields of ethers 5a-i were 70−89% and 80−96%, respectively depending on the used procedures. Conclusion: The described methods are simple, clean and environmentally friendly alternatives for the preparation of 2-amino-4-aryl-7-hydroxy-4H-chromene-3-carbonitriles. The conditions for the transformation of these compounds into propargyl ethers include dried DMF as a solvent, NaH as a base and reaction time of 2 h at the room temperature. A series of 2-amino-4-aryl-7-hydroxy-4-aryl-4H-chromene-3-carbonitriles were obtained based on investigated reaction condition.

The crystal structures of two new coumarin derivatives: 2-(4-{2-[(2-oxo-2H-chromen-4-yl)oxy]acetyl}piperazin-1-yl)acetamide and N-(2,4-dimethoxybenzyl)-2-[(2-oxo-2H-chromen-4-yl)oxy]acetamide

The title compounds, 2-(4-{2-[(2-oxo-2H-chromen-4-yl)oxy]acetyl}piperazin-1-yl)acetamide, C17H19N3O5, (I), and N-(2,4-dimethoxybenzyl)-2-[(2-oxo-2H-chromen-4-yl)oxy]acetamide, C20H19NO6, (II), are new coumarin derivatives. In compound (I), the six-membered piperazine adopts a chair conformation. The dihedral angles between the mean planes of the chromene ring and amide plane is 82.65 (7)° in (I) and 26.2 (4)° in (II). The dihedral angles between the mean planes of the chromene ring and the four planar C atoms of the piperazine ring in (I) and the benzene ring in (II) are 87.66 (6) and 65.0 (4)°, respectively. There are short intramolecular contacts in both molecules forming S(5) ring motifs, viz. N—H...N and C—H...O in (I), and N—H...O and C—H...N in (II). In the crystals of both compounds, molecules are linked by N—H...O hydrogen bonds, forming chains along [1\overline{1}0] in (I) and [010] in (II). The chains are linked by C—H...O hydrogen bonds, forming layers parallel to the ab plane in the crystals of both compounds. In the crystal of (I), there are also C—H...π and offset π–π interactions [intercentroid distance = 3.691 (1) Å] present within the layers. In the crystal of (II), there are only weak offset π–π interactions [intercentroid distance = 3.981 (6) Å] present within the layers. The intermolecular contacts in the crystals of both compounds have been analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots.

Methyl (6R*,6aR*,12bR*)-2,4-dimethyl-6-(2-methylphenyl)-1,3-dioxo-2,3,4,6a,7,12b-hexahydro-1H,6H-chromeno[4′,3′:4,5]pyrano[2,3-d]pyrimidine-6a-carboxylate

In the title compound, C24H24N2O6, the mean planes of the pyran rings (AandB) are inclined to one another by 69.2 (1)°, while the aromatic ring (D) of the chromene ring system makes dihedral angles of 63.42 (11) and 66.81 (12)° with the pyrimidine (C) and benzene (E) rings, respectively. Pyran ringAhas an half-chair conformation, while pyran ringBhas an envelope conformation, with the spiro C atom as the flap. In the crystal, molecules are linked by C—H...O hydrogen bonds, forming a supramolecular three-dimensional network. There are also a number of C—H...π interactions present.

9-Fluoro-2,4,4a,6-tetrahydrospiro[benzo[c]chromene-3,2′-[1,3]dioxolane]

In the title compound, C15H15FO3, the dihedral angle between the mean plane through all the non-H atoms of the dioxolane ring with those of the rest of the atoms of the chromene ring system, including the substituent F atom, is 81.1 (1)°. The pyran ring has an envelope conformation with the O atom as the flap. The cyclohexene ring has a half-chair conformation, while the dioxolane ring has a twisted conformation on an –O—CH2– bond. In the crystal, molecules are linkedviaC—H...O hydrogen bonds, forming chains along [100]. The chains are linked by C—H...π interactions, involving the fluorobenzene ring, forming layers parallel to theacplane.

(6-Fluoro-2-oxo-2H-chromen-4-yl)methyl diethylcarbamodithioate

The title compound, C15H16FNO2S2, crystallizes with two independent molecules (AandB) in the asymmetric unit. They differ essentially in the orientation of the ethyl groups. The chromene rings are planar (r.m.s. deviations = 0.013 Å for both molecules), with the maximum deviation from the ring planes being 0.014 (2) and 0.018 (2) Å for atoms C9Aand C9B, respectively. The mean plane of the chromene ring makes dihedral angles of 80.01 (7) and 76.97 (8)° with the carbamodithioate moiety [(N—C(=S)—S] of moleculesAandB, respectively. In the crystal, the two molecules are linked by C—H...S hydrogen bonds, forming a ladder-like arrangement propagating along thea-axis direction. Within the ladders there are offset π–π interactions involving the coumarins rings of theBmolecules [intercentroid distances vary from 3.705 (2) to 3.860 (1) Å]. Neighbouring ladders are linkedviaoffset π–π interactions involving the coumarins rings of theAmolecules [intercentroid distances vary from 3.539 (1) to 3.601 (1) Å]. These latter interactions lead to the formation of layers parallel to theacplane.

4-[(4-Hydroxymethyl-2H-1,2,3-triazol-2-yl)methyl]-6-isopropyl-2H-chromen-2-one

In the title compound, C16H17N3O3, the chromene ring is planar, with a maximum deviation of 0.017 (4) Å for the ring O atom. The triazole and the chromene rings, bridged by a methylene C atom, are inclined to one another by 78.3 (2)°. In the crystal, methylene–triazole C—H...N hydrogen bonds lead to the formation of helical supramolecular chains along thebaxis. The sample was refined as an inversion twin. The terminal methylhydroxy group is disordered over two sets of sites [site occupancy = 0.610 (13) for the major component].