Diels-Alder/Ene Reactivities of 2-(1'-Cycloalkenyl)thiophenes and 2-(1'-Cycloalkenyl)benzo[b]thiophenes with N-Phenylmaleimides: Role of Cycloalkene Ring Size on Benzothiophene and Dibenzothiophene Product Distributions.

Scaffolds of thiophene and benzothiophene are the important class of bioactive compounds found abundant in nature. The Diels-Alder reactions of 2-(1'-cycloalkenyl)thiophenes and 2-(1'-cycloalkenyl)benzo[b]thiophenes having the alkene groups present in five-, six-, seven-, eight-, and twelve-membered rings with substituted N-phenylmaleimides are characterized. The size of the cycloalkene rings plays a critical role in dictating the product distributions of expected and isomerized Diels-Alder adducts. 2D NMR studies indicate that the isolated isomers for 2-(1'-cycloalkenyl)thiophenes having five-, six-, and seven-membered rings are aromatized benzothiophene products, whereas eight- and twelve-membered rings are un-rearranged adducts. In addition, the product of subsequent ene-reaction with the N-phenylmaleimide is isolated for the five- and six-membered ring cases. Interestingly, in the 2-(1'-cycloalkenyl)benzo[b]thiophene having five-, six-, seven-, eight-, and twelve-membered rings, the un-rearranged dibenzothiophene Diels-Alder adduct is isolated in every instance. Molecular mechanics and density functional theory (M06-2X and PBE0-D3) calculations are performed to understand the differential reactivity of the various dienes for both the initial Diels-Alder reaction and a possible, subsequent ene reaction.

Crystal structure of (±)-(3aR,5R,8bR)-5-hydroper-oxy-2-phenyl-6-tosyl-4,5,6,8b-tetra-hydro-pyrrolo-[3,4-e]indole-1,3(2H,3aH)-dione.

The title compound, C23H20N2O6S, crystallizes as a racemate in the space group P-1, with an overall L- or J-shape to each mol-ecule. Centrosymmetric pairs of mol-ecules are tandem hydrogen bonded between the hydro-per-oxy H atom and carbonyl O atom. A different centrosymmetric pairing has stacked S-tolyl rings, and a third pairing is L,J-inter-locked by the short leg. Except for stacked tolyl pairs, neighboring π-systems are much closer to orthogonal than coaxial. The title compound is the first example of a hydro-peroxide obtained from the autoxidation of a Diels-Alder adduct of a 2-vinyl-pyrrole.

Crystal structure of (1S,2R,6R,7R,8S,12S)-4,10,17-triphenyl-15-thia-4,10-diaza-penta-cyclo[5.5.5.0(1,16).0(2,6).0(8,12)]hepta-deca-13,16-diene-3,5,9,11-tetrone p-xylene hemisolvate.

The title tetrone compound, C32H22N2O4S· 0.5C8H10, is the major product (50% yield) of an attempted Diels-Alder reaction of 2-(α-styr-yl)thio-phene with N-phenyl-male-imide (2 equivalents) in toluene. Recrystallization of the resulting powder from p-xylene gave the title hemisolvate; the p-xylene mol-ecule is located about an inversion center. In the crystal, the primary tetrone contacts are between a carbonyl O atom and the four flagpole H atoms of the bi-cyclo-[2.2.2]octene core, forming chains along [001].

Four polymorphs (polytypes) of 5,6-dimethylbenzofurazan 1-oxide.

5,6-Dimethylbenzofurazan 1-oxide (Me2BF), C(8)H(8)N(2)O(2), occurs in four polymorphic forms that are polytypes of each other. Each polymorph of Me2BF contains molecules disordered about pseudo-twofold axes and arranged head-to-tail in ribbons, with the ribbons forming approximately planar layers held together by weak C-H···N and C-H···O interactions. Adjacent layers interact in different ways in the different polymorphs. In addition to twinning in the individual polymorphs, four examples of allotwining, that is, oriented overgrowths between different polymorphs, were found.

3,5-Di-bromo-4-carbamoyl-benzoic acid 2-propanol monosolvate.

In the title solvated crystal, C8H5Br2NO3·C3H8O, the acid mol-ecules form inversion dimers by pairwise N-H⋯O hydrogen bonds between carbamoyl groups and the carboxyl and carbamoyl groups link to form head-to-tail inversion dimers. The 2-propanol hydroxyl group inter-poses between adjacent head-tail pairs, resulting in C 3 3(10) chains of hydrogen bonds propagating along [100]. The mol-ecules of 2-propanol are disordered over two sets of sites in a 0.598 (8):0.402 (8) ratio. The best-fit planes of the carbamoyl group and benzene ring are inclined by 88.26 (11)°. This is a greater inclination than was previously reported with CH3, Cl, F or H in place of the Br atoms, although those analogues did not have a para carboxyl group.

Fe-Catalyzed Domino Intramolecular Nucleophilic Substitution of 4-Hydroxychromen-2-one and Pyran-2-one/Ring Opening of Activated Arene: An Easy Access to 2,3-Disubstituted Furo[3,2,-c]coumarins and Furo[3,2,-c]pyran-4-ones via Nonsymmetric Triarylmethanes.

A one-pot synthesis of functionalized 2,3-disubstituted furo[3,2,-c]coumarins and furo[3,2,-c]pyran-4-ones under hydrated ferric sulfate catalysis was performed. It was revealed that the reaction proceeds with intramolecular cyclofunctionalization of nonsymmetric triarylmethanes via ring opening of 2-methylfuran followed by recyclization, resulting in the selective formation of desired products. The versatility of this method was demonstrated via the succinct synthesis of an anticoagulant agent analogue and 2,3-disubstituted benzofurans.

Crystal structure of 2,3,5,6-tetra-bromo-tereph-thalo--nitrile.

The title crystal (systematic name: 2,3,5,6-tetra-bromo-benzene-1,4-dicarbonitrile), C8Br4N2, is the first bromo analog in a study of cyano-halo (C≡N⋯X) non-bonded contacts in crystals of halogenated di-cyano-benzenes. The complete mol-ecule is generated by a crystallographic center of symmetry. In the extended structure, each Br atom accepts one C≡N⋯Br inter-action, and each N atom is bis-ected by two. This contact network forms a nearly planar sheet structure propagating in the (01) plane, similar to that reported in hexa-methyl-benzene co-crystals of the tetra-chloro analog.

5-Iodobenzofurazan 1-oxide: polymorphs, pseudosymmetry and disorder.

5-Iodobenzofurazan 1-oxide (systematic name: 5-iodobenzo-1,2,5-oxadiazole 1-oxide), C(6)H(3)IN(2)O(2), occurs in two polymorphic forms, both monoclinic in P2(1)/c with Z' = 2. The intermolecular interactions in the two polymorphs are quite different. In polymorph (I), there are strong intermolecular I...O interactions, with I...O distances of 3.114 (8) and 3.045 (8) A. In polymorph (II), there are strong intermolecular I...N interactions, with I...N distances of 3.163 (4) and 3.175 (5) A. In (I), there is about 15% disorder in one molecule and about 5% in the other. In both polymorphs, there are pseudosymmetric relationships between the crystallographically independent molecules.

Crystal structures of methyl 3,5-di-bromo-4-cyano-benzoate and methyl 3,5-di-bromo-4-iso-cyano-benzoate.

The title crystals, C9H5Br2NO2, are the first reported 2,6-dihalophenyl cyanide-isocyanide pair that have neither three- nor two-dimensional isomorphism. Both crystals contain contacts between the carbonyl O atom and a Br atom. In the crystal of the cyanide, R22(10) inversion dimers form based on C≡N⋯Br contacts, a common packing feature in this series of crystals. In the isocyanide, the corresponding N≡C⋯Br contacts are not observed. Instead, the iso-cyano C atom forms contacts with the meth-oxy C atom. RNC was refined as a two-component pseudo-merohedral twin.

Crystal structures of 2,4,6-tri-iodo-benzo-nitrile and 2,4,6-tri-iodo-phenyl isocyanide.

The title crystals, C7H2I3N, are isomorphous. Both mol-ecules lie across two crystallographic mirror planes and a twofold axis. The principal supra-molecular inter-action is centric R22(10) CN/NC⋯I short contacts involving both ortho I atoms, with two contacts bis-ecting each cyano and iso-cyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzo-nitriles, in which I atoms give the strongest CN⋯X and NC⋯X inter-actions (X = F, Cl, Br, I).

A 2:1 co-crystal of 3,5-di-bromo-4-cyano-benzoic acid and anthracene.

The title co-crystal, C8H3Br2NO2·0.5C14H10, was self-assembled from a 2:1 mixture of the components in slowly evaporating di-chloro-methane. The mol-ecules adopt a sheet structure parallel to (1-12) in which carb-oxy hydrogen-bonded dimers and anthracene mol-ecules stagger in both dimensions. Within the sheets, six individual cyano acid mol-ecules surround each anthracene mol-ecule. Cyano acid mol-ecules form one of the two possible R22(10) rings between neighboring cyano and bromo groups. Compared to the di-chloro analog [Britton (2012 ▸). J. Chem. Crystallogr.42, 851-855], the dihedral angle between the best-fit planes of acid and anthracene mol-ecules has decreased from 7.1 to 0.9 (2)°.

Crystal structures of 2,6-di-bromo-4-methyl-benzo-nitrile and 2,6-di-bromo-4-methyl-phenyl isocyanide.

In the title crystals, C8H5Br2N, which are isomorphous, the steric bulk of the methyl group causes neighboring mol-ecules to become mutually inclined. This prevents the formation of planar or nearly planar sheets, which were observed in the tri-chloro and tri-bromo analogs. Instead of CN/NC⋯Br contacts, tetra-meric Br⋯Br contacts are observed. These contacts form tetra-gonally puckered sheets parallel to (001). The CN/NC and methyl groups are grouped at the peaks and troughs. Both mol-ecules lie across crystallographic mirror planes; thus, the methyl H atoms are disordered over two sets of sites with equal occupancy. The title nitrile is a redetermination. The refinement converged at R[F2 > 2σ(F2)] = 0.020, whereas the original determination [Gleason & Britton, (1976 ▸). Cryst. Struct. Commun.5, 229-232] had R = 0.112.

Two new polytypes of 2,4,6-tri-bromo-benzo-nitrile.

Three polymorphs of 2,4,6-tri-bromo-benzo-nitrile (RCN), C7H2Br3N, two of which are novel and one of which is a redetermination of the original structure first determined by Carter & Britton [(1972). Acta Cryst. B28, 945-950] are found to be polytypic. Each has a layer structure which differs only in the stacking of the layers. Each layer is composed of mol-ecules associated through C N⋯Br contacts which form R (2) 2(10) rings. Two such rings are associated with each N atom; one with each ortho-Br atom. No new polytypes of 1,3,5-tri-bromo-2-iso-cyano-benzene (RNC) were found but a re-determination of the original structure by Carter et al. [(1977). Cryst. Struct. Commun. 6, 543-548] is presented. RNC was found to be isostructural with one of the novel polytypes of RCN. Unit cells were determined for 23 RCN samples and 11 RNC samples. Polytypes could not be distinguished based on crystal habits. In all four structures, each mol-ecule of the asymmetric unit lies across a mirror plane.

Crystal structure of rac-3-[2,3-bis-(phenyl-sulfan-yl)-3H-indol-3-yl]propanoic acid.

The title compound, C23H19NO2S2, was obtained as an unexpected regioisomer from an attempted synthesis of an inter-mediate for a substituent-effect study on ergot alkaloids. This is the first report of a 1H-indole mono-thio-ating at the 2- and 3-positions to give a 3H-indole. In the crystal, the acid H atom is twisted roughly 180° from the typical carb-oxy conformation and forms centrosymmetric O-H⋯N hydrogen-bonded dimers with the indole N atom of an inversion-related mol-ecule. Together with a weak C-H⋯O hydrogen bond involving the carbonyl O atom, chains are formed along [100].

Crystal structure of rac-(3a'R,9a'R)-3a'-(indol-3-yl)-1',2',3',3a',4',9a'-hexa-hydro-spiro-[cyclo-pentane-1,9'-penta-leno[1,2-b]indole] p-xylene hemisolvate.

The title compound, C26H26N2·0.5C8H10, is the first reported characterized 2:2 product from acid-catalyzed condensation of indole with cyclo-penta-none and no other 2:2 products were observed. Recrystallization from p-xylene gave the title hemisolvate with the p-xylene mol-ecule located about an inversion center. The terminal penta-lene ring is envelope-flap disordered at the C atom farthest from the skeletal indole unit, with a refined occupancy ratio of 0.819 (4):0.181 (4). The major component has this C atom bent away from the spiro-fused cyclo-pentane ring. In the crystal, mol-ecules are connected by N-H⋯π inter-actions, forming chains along [100], and N-H⋯π and C-H⋯π inter-actions, forming chains along [001], which results in the formation of slabs parallel to (010).

Structure Determination of the Products from the Acid-Catalyzed Condensation of Indole with Acetone.

Four of the previously reported compounds obtained from the acid-catalyzed condensation of indole with acetone are now assigned the following structures: cis-4,4a,9,9a-tetrahydro-2-(1H-indol-3-yl)-4,4-dimethyl-3H-carbazole (2a), 1,1',4,4'-tetrahydro-1,1,1',1'-tetramethyl-3,3'(2H,2'H)-spirobi[cyclopent[b]indole] (4), 4,4a-dihydro-2-(3-1H-indolyl)-4,4-dimethyl-3H-carbazol-4a-ol (7), and 5-(2-aminophenyl)-1,3,4,5-tetrahydro-1,1,4,4-tetramethylcyclopent[kl]acridine (8). The structure of the novel rearrangement product 8 was solved by an X-ray crystal structure determination. The two previously reported autoxidation products of 4 are now assigned the following structures: 1,3',4,4'-tetrahydro-1,1,4',4'-tetramethyl-cis-dispiro[cyclopent[b]indole-3(2H),2'(5'H)-furan-5',3"-[3H]-indol]-2"(1"H)-one (5) and 1,4-dihydro-1,1,5',5'-tetramethylspiro[cyclopent[b]indole-3(2H),3'(4'H)-1-benzazocine]-2'(1'H),6'(5'H)-dione (6).

Reactivity of nitrovinylquinones with cyclic and acyclic enol ethers.

The nitrovinyl-substituted quinones 2-(2-nitrovinyl)-1,4-benzoquinone and 2-(2-nitrovinyl)-1,4-naphthoquinone react with a variety of cyclic and acyclic enol ethers via two competing pathways. In one pathway, the nitrovinylquinone acts as an inverse electron-demand [4 + 2] diene. This gives quinoid carbocycles, which readily tautomerize to their hydroquinone form. The other pathway involves conjugate (Michael) addition of the enol ether to the nitrovinylquinone, followed by ring closure. This gave dihydrobenzofurans, which can eliminate an alcohol to give benzofurans. Hindered enol ethers tended to favor the conjugate addition pathway, while less hindered enol ethers favored cycloaddition.

Five (1H-pyrrol-2-yl)pyridines.

The title (1H-pyrrol-2-yl)pyridines, C(9)H(8)N(2), substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen-bonded arrangements with geometrically similar, nearly linear, N(pyrrole)-H...N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(2)(2)(10), C(6), C(7), C(7), and R(4)(4)(28), respectively.