Eugeniya V. Nikitina

Aromatization of IMDAF adducts in aqueous alkaline media

In this paper, we propose a simple synthesis of isoindoline-4-carboxylic acids by means of the aromatization of 3a,6-epoxyisoindoles in alkaline media. The method is facile from an experimental point of view: a short-term (0.5–2h) reflux of epoxyisoindoles in 5% aqueous solutions of alkali leads to the target products in 40–90% yields. The absence of by-products, ease of isolation of the target products and applicability to acidophobic group bearing substrates favorably distinguishes the proposed procedure from previously utilized acid-catalyzed methods. The proposed strategy has been successfully utilized for isoindole containing compounds and nuevamine-type alkaloids.

Wagner–Meerwein rearrangement in 2,6a-epoxyoxireno[e]isoindole series

A cation-catalyzed Wagner–Meerwein skeletal rearrangement in octahydro-2,6a-epoxyoxireno[e]isoindole series was studied. It was shown that the reaction proceeds ambiguously when effected by boron trifluoride etherate in acetic anhydride: the target 4,5-bis(acetoxy)-4,6-epoxycyclopenta[c]pyridines as well as the products of their further degradation, cyclopenta[c]pyridines, were isolated from the reaction mixture in 10–15% yields as single diastereomers.

Methyl (9aR*,10S*,11R*,13aS*,13bS*)-9-oxo-6,7,9,9a,10,11-hexa­hydro-5H,13bH-11,13a-ep­oxy­pyrrolo­[2′,1′:3,4][1,4]diazepino[2,1-a]isoindole-10-carboxyl­ate

The title compound, C17H18N2O4, is the methyl ester of the adduct of intramolecular Diels–Alder reaction between maleic anhydride and 1-(2-furyl)-2,3,4,5-tetrahydro-1H-pyrrolo[1,2-a][1,4]diazepine. The molecule comprises a fused pentacyclic system containing four five-membered rings (viz. pyrrole, 2-pyrrolidinone, tetrahydrofuran and dihydrofuran) and one seven-membered ring (1,4-diazepane). The pyrrole ring is approximately planar (r.m.s. deviation = 0.003 Å) while the 2-pyrrolidinone, tetrahydrofuran and dihydrofuran five-membered rings have the usual envelope conformations. The central seven-membered diazepane ring adopts a boat conformation. In the crystal, molecules are bound by weak intermolecular C—H⋯O hydrogen-bonding interactions into zigzag chains propagating in [010]. In the crystal packing, the chains are stacked along the a axis.

Methyl 4,5-diacet­oxy-1-oxo-2-phenyl­perhydro-4,6-epoxy­cyclo­penta­[c]pyridine-7-carboxyl­ate ethanol solvate

The title compound, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as an ethanol monosolvate, C20H21NO8·C2H6O. The title molecule comprises a fused tricyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) in the usual envelope conformations and one six-membered ring (piperidinone) adopting a flattened twist–boat conformation.

Crystal structure of methyl (3RS,4SR,4aRS,11aRS,11bSR)-5-oxo-3,4,4a,5,7,8,9,10,11,11a-deca-hydro-3,11b-ep-oxy-azepino[2,1-a]iso-indole-4-carboxyl-ate.

The title compound, C15H19NO4, is the a product of the esterification of the corresponding carbonic acid with methanol. The molecule comprises a fused tetracyclic system containing three five-membered rings (2-pyrrolidinone, tetrahydrofuran and dihydrofuran) and one seven-membered ring (azepane). The five-membered rings have the usual envelope conformations, with the quaternary C atom being the flap atom for the 2-pyrrolidinone ring, and the ether O atom being the common flap atom for the remaining rings. The seven-membered azepane ring adopts a chair conformation with the methine and middle methylene C atoms lying above and below the mean plane defined by the remaining five atoms. The carboxylate substituent is rotated by 77.56 (5)° with respect to the base plane of the tetrahydrofuran ring. In the crystal, the molecules are bound by weak C—H⋯O hydrogen-bonding interactions into puckered layers parallel to (001).

Dimethyl 11,13-dimethyl-16-[1,2-bis­(methoxy­carbon­yl)ethen­yl]-12-oxo-16,17-dioxa-18-aza­hexa­cyclo­[7.5.1.11,4.16,9.110,14.05,15]octa­deca-2,7-diene-2,3-dicarboxyl­ate

The title compound, C27H29NO11, is a product of the tandem ‘domino’ Diels–Alder reaction. The molecule comprises a fused hexacyclic system containing four five-membered rings (two dihydrofuran and two tetrahydrofuran) in the usual envelope conformations and two six-membered rings (tetrahydropyridinone and piperidine) adopting slightly flattened boat and chair conformations, respectively. The dispositions of the carboxylate substituents relative to each other are determined by both steric reasons and intermolecular C—H⋯O hydrogen bonding and attractive antiparallel C=O⋯C=O interactions [C⋯O = 2.995 (2) Å].

Intramolecular [4+2] cycloaddition in N-allyl- and N-propargyl-α-furyl lactams

The size of nitrogen heterocycle in N-allyl- and N-propargyl-α-furyl lactams, as well as the nature of the unsaturated substituent linked to the nitrogen atom affected the possibility of thermal intramolecular [4+2] cycloaddition between multiple bond and the furan ring. N-Allyl-γ-(α-furyl)butyrolactam was shown to be unreactive at temperatures from 140 to 230°С. Substituted δ-valero- and ε-caprolactams underwent partial Diels–Alder cyclization, forming tautomeric mixtures that contained both the initial open-chain form and the cyclic form (diastereomeric 3a,6-epoxyisoindoles fused with an aza ring) in ratios between 19:81 and 55:45. N-Propargyl-α-furyl lactams did not participate in thermal IMDAF reaction regardless of the ring size and the temperature of the synthesis.

rac-Methyl (3aR*,4S*,5R*,7aR*)-5,7a-bis-(acet-yloxy)-3-oxo-2-phenyl-octa-hydro-1H-iso-indole-4-carboxyl-ate.

The title molecule, C20H23NO7, the product of nucleophilic cleavage of the 3a,6-epoxy bridge in 1-oxo-2-phenyloctahydro-3a,6-epoxyisoindole-7-carboxylate, comprises a cis-fused bicyclic system containing a 2-pyrrolidinone ring in an envelope conformation (with the C atom bearing the carboxylate substituent as the flap) and a cyclohexane ring in a chair conformation. The carboxylate substituent occupies the equatorial position, whereas the two acetyloxy substituents are in axial positions. The N atom has a trigonal-planar geometry, the sum of the bond angles being 359.3 (3)°. The dihedral angle between the mean plane of the four planar atoms of the pyrrolidinone ring and the phenyl ring is 25.98 (6)°. In the crystal, molecules are linked into zigzag chains along the c-axis direction by C—H⋯O hydrogen bonds.

(4R*,4aR*,7aS*)-5-Oxo-6-phenyl-4a,5,6,7,7a,8-hexa­hydro-4H-furo[2,3-f]isoindole-4-carb­oxy­lic acid

The asymmetric unit of the title compound, C17H15NO4, contains two independent molecules with similar geometric parameters. In both molecules, the conformation of the cyclohexene ring is half-chair, while the pyrrolidinone ring adopts an envelope conformation with the γ-carbon atom of the α-pyrrolidinone ring as the flap. In the crystal, O—H⋯O hydrogen bonds between the carboxylic and carbonyl groups link alternate independent molecules into chains propagating in the b-axis direction. The crystal packing also features weak C—H⋯π interactions.

Methyl 7,8-diacet­oxy-11-oxo-5-(2-oxo­pyrrolidin-1-yl)-7,9-epoxy­cyclo­penta­[4,5]pyrido[1,2-a]quinoline-10-carboxyl­ate sesquihydrate

The title compound, C26H28N2O9·1.5H2O, the product of an acid-catalysed Wagner–Meerwein skeletal rearrangement, crystallizes as a sesquihydrate with the O atom of one of the two independent water molecules occupying a special position on a twofold axis. The organic molecule comprises a fused pentacyclic system containing two five-membered rings (cyclopentane and tetrahydrofuran) and three six-membered rings (piperidinone, tetrahydropyridine and benzene). The five-membered rings have the usual envelope conformations, and the central six-membered piperidinone and tetrahydropyridine rings adopt boat and sofa conformations, respectively. In the crystal, there are three independent O—H⋯O hydrogen bonds, which link the organic molecules and water molecules into complex two-tier layers parallel to (001). The layers are further linked into a three-dimensional framework by attractive intermolecular carbonyl–carbonyl interactions.