S. Sivakumar

Domino reactions in water: diastereoselective synthesis of densely functionalized indolyldihydrofuran derivatives†

A library of trans-5-aroyl-2-(indol-3-yl)-4-aryl-4,5-dihydrofuran-3-carbonitriles was diastereoselectively synthesized in excellent yields from the reaction of 2-(3-indolylcarbonyl)-3-aryl-2-propenenitriles with (2-aryl-2-oxoethyl)pyridinium bromides in the presence of triethylamine via a simple, user-friendly domino process carried out in water. Extraction and chromatographic steps were avoided, since the final products could be simply filtered from the aqueous reaction medium and recrystallized. This one-pot transformation generates one C–C and one C–O bond and presumably proceeds by a domino sequence involving the generation of a pyridinium ylide, a Michael addition and a final annulation via intramolecular nucleophilic substitution.

Four-component domino strategy for the combinatorial synthesis of novel 1,4-dihydropyrano[2,3-c]pyrazol-6-amines.

An efficient one-pot four-component domino protocol for the combinatorial synthesis of novel 1,4-dihydropyrano[2,3-c]pyrazol-6-amines has been achieved. This transformation presumably occurs via cyclization-Knoevenagel condensation-Michael addition-tautomerism-intramolecular O-cyclization-elimination sequence of reactions. The significant features of this reaction include expedient one-pot process, short reaction time, no column chromatographic purification, excellent yield, and readily available starting materials.

A one-pot three-component domino protocol for the synthesis of penta-substituted 4H-pyrans

A library of novel 2-(1H-indol-3-yl)-6-(methylamino)-5-nitro-4-aryl-4H-pyran-3-carbonitriles and 6-(methylamino)-4-(aryl)-5-nitro-2-phenyl-4H-pyran-3-carbonitriles were synthesized in excellent yields via domino one-pot three-component reactions of 3-(1H-indol-3-yl)-3-oxopropanenitrile or benzoylacetonitrile, aromatic aldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine respectively. This reaction presumably occurs via domino Knoevenagel condensation–Michael addition–intramolecular O-cyclization sequence of reactions. The significant advantages of this reaction include one-pot process, simple work-up procedure, excellent yields and no column chromatographic purification.

4-(4-Fluoro­phen­yl)-6-methyl­amino-5-nitro-2-phenyl-4H-pyran-3-carbo­nitrile

In the title compound, C19H14FN3O3, the central pyran ring adopts a boat conformation with the O atom and the quaternary C atom diagonally opposite displaced by 0.068 (1) and 0.075 (1) Å, respectively, above the mean plane defined by the other four ring atoms. The co-planar atoms of the pyran ring and the fluorophenyl ring are nearly perpendicular, as evidenced by the dihedral angle of 87.11 (1)°. The amine group forms an intramolecular N—H⋯O(nitro) hydrogen bond. In the crystal, molecules are linked into parallel chains along [100] by weak N—H⋯N and C—H⋯N(nitro) hydrogen bonds, generating C(8) and C(9) graph-set motifs, respectively.

5-Amino-6-benzoyl-8-nitro-2,3-di­hydro-1H-spiro­[imidazo[1,2-a]pyridine-7,3′-indolin]-2′-one dimethyl sulfoxide monosolvate

In the title compound C21H17N5O4·C2H6OS, the central six-membered ring derived from 1,4-dihydropyridine adopts a distorted boat conformation with a small puckering amplitude of 0.127 (3) Å. The sums of bond angles around the pyridine N atom [358.7 (2)°] and the other imidazolidine N atom [60 (2)°] indicate that these atoms are in sp2 hybridization, leading to an essentially planar imidazolidine ring. The last heterocycle, an oxindole moiety, is also nearly planar with an r.m.s. deviation of 0.0185 (1) Å. The amine NH2 group forms an intramolecular hydrogen bond with the benzoyl group, giving a S(6) motif. In the crystal, N—H⋯O hydrogen bonds lead to the formation of chains along the c-axis direction. Within the chains there are further N—H⋯O and C—H⋯O hydrogen bonds enclosing R 2 2(14) ring motifs. The chains are linked via N—H⋯O and C—H⋯O hydrogen bonds involving the dimethyl sulfoxide solvent molecule which acts as both an acceptor and a donor..

N—H...O and N—H...N interactions in three pyran derivatives

The three pyran structures 6-methylamino-5-nitro-2,4-diphenyl-4H-pyran-3-carbonitrile, C19H15N3O3, (I), 4-(3-fluorophenyl)-6-methylamino-5-nitro-2-phenyl-4H-pyran-3-carbonitrile, C19H14FN3O3, (II), and 4-(4-chlorophenyl)-6-methylamino-5-nitro-2-phenyl-4H-pyran-3-carbonitrile, C19H14ClN3O3, (III), differ in the nature of the aryl group at the 4-position. The heterocyclic ring in all three structures adopts a flattened boat conformation. The dihedral angle between the pseudo-axial phenyl substituent and the flat part of the pyran ring is 89.97 (1)° in (I), 80.11 (1)° in (II) and 87.77 (1)° in (III). In all three crystal structures, a strong intramolecular N-H···O hydrogen bond links the flat conjugated H-N-C=C-N-O fragment into a six-membered ring. In (II), molecules are linked into dimeric aggregates by N-H··· O(nitro) hydrogen bonds, generating an R2(2)(12) graph-set motif. In (III), intermolecular N-H···N and C-H···N hydrogen bonds link the molecules into a linear chain pattern generating C(8) and C(9) graph-set motifs, respectively.

5′′-(4-Meth­oxy­benzyl­idene)-7′-(4-meth­oxy­phen­yl)-1′′-methyl-5′,6′,7′,7a'-tetra­hydro­dispiro­[acenaphthene-1,5′-pyrrolo­[1,2-c][1,3]thia­zole-6′,3′′-piperidine]-2,4′′-dione

In the title compound, C37H34N2O4S, the piperidine ring adopts a half-chair conformation. The thiazole ring adopts a slightly twisted envelope conformation and the pyrrole ring adopts an envelope conformation; in each case, the C atom linking the rings is the flap atom. An intramolecular C—H⋯O interaction is noted. The crystal structure is stabilized by C—H⋯O and C—H⋯π interactions.

Crystal structure of 5-benzoyl-2,4-di­phenyl-4,5-di­hydro­furan-3-carbo­nitrile

In the title compound, C24H17NO2, the carbonyl O atom of the benzoyl group is cis with respect to the furanyl O atom, and the associated O—C—C—O torsion angle is 4.62 (19)°. The puckering of the dihydrofuran ring is close to twisted (4 T 5), with parameters Q = 0.1856 (16) Å and φ = 313.5 (5)°. Molecules are interconnected via a C—H⋯N and a C—H⋯O hydrogen bond, leading to layers parallel to the (200) plane and characterized by R 4 4(28) and R 4 4(36) graph-set motifs. The furan O atom does not participate in intermolecular hydrogen bonding. The crystal lattice encompasses a solvent-accessible void of 24.7 (8) Å3.

Crystal structure of 5-amino-5'-chloro-6-(4-chloro-benzo-yl)-8-nitro-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indolin]-2'-one including an unknown solvent mol-ecule.

The asymmetric unit of the title compound, C21H15Cl2N5O4, contains two independent molecules (A and B) having similar conformations. The amine (NH2) group forms an intramolecular hydrogen bond with the benzoyl group, giving an S(6) ring motif in both molecules. The central six-membered rings adopt sofa conformations and the imidazole rings are planar (r.m.s deviations = 0.0150 and 0.0166 Å). The pyridine and imidazole rings are inclined to one another by 3.54 (1) and 3.03 (1)° in molecules A and B, respectively. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming chains along the a axis which enclose R 2 2(16) ring motifs. The rings are linked by weak N—H⋯O and C—H⋯O hydrogen bonds and C—H⋯π interactions forming sheets lying parallel to (001). A region of disordered electron density, most probably disordered solvent molecules, occupying voids of ca 753 Å3 for an electron count of 260, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Their formula mass and unit-cell characteristics were not taken into account during refinement.

5-Amino-5'-bromo-6-(4-methyl-benzo-yl)-8-nitro-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indolin]-2'-one including an unknown solvate.

In the title compound, C22H18BrN5O4, the central six-membered ring, derived from 1,4-dihydropyridine, adopts a distorted boat conformation with a puckering amplitude of 0.197 (3) Å, the imidazole ring adopts a twisted conformation with a puckering amplitude of 0.113 (3) Å, and the oxindole moiety is planar with an r.m.s. deviation of 0.0125 Å. Two intramolecular N—H⋯O hydrogen bonds are formed, each closing an S(6) loop. In the crystal, strong N—H⋯O hydrogen bonds lead to the formation of zigzag chains along the c axis. These are consolidated in the three-dimensional crystal packing by weak N—H⋯O hydrogen bonding, as well as by C—H⋯O, C—H⋯Br and C—H⋯π interactions. A small region of electron density well removed from the main molecule was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155] following unsuccessful attempts to model it as a plausible solvent molecule. The unit-cell characteristics do not take into account this feature of the structure.