A new, chiral aminoanthracene for the Diels–Alder/retro-Diels–Alder sequence in lactam and butenolide synthesis

Diels-Alder Reactivity of a Chiral Anthracene Template with Symmetrical and Unsymmetrical Dienophiles: A DFT Study

In this work, we used Density Functional Theory calculations to assess the factors that control the reactivity of a chiral anthracene template with three sets of dienophiles including maleic anhydrides, maleimides and acetoxy lactones in the context of Diels-Alder cycloadditions. The results obtained here (at the M06-2X/6-311++G(d,p) level of theory) suggest that the activation energies for maleic anhydrides and acetoxy lactones are dependent on the nature of the substituent in the dienophile. Among all studied substituents, only -CN reduces the energy barrier of the cycloaddition. For maleimides, the activation energies are independent of the heteroatom of the dienophile and the R group attached to it. The analysis of frontier molecular orbitals, charge transfer and the activation strain model (at the M06-2X/TZVP level based on M06-2X/6-311++G(d,p) geometries) suggest that the activation energies in maleic anhydrides are mainly controlled by the amount of charge transfer from the diene to the dienophile during cycloaddition. For maleimides, there is a dual control of interaction and strain energies on the activation energies, whereas for the acetoxy lactones the activation energies seem to be controlled by the degree of template distortion at the transition state. Finally, calculations show that considering a catalyst on the studied cycloadditions changes the reaction mechanism from concerted to stepwise and proceed with much lower activation energies.

Evaluating hydrogen bonding control in the diastereoselective Diels-Alder reactions of 9-(2-aminoethyl)-anthracene derivatives

Several 9-(2-aminoethyl)anthracene derivatives were prepared with different nitrogen substitutents including alkyl, acetamide, trifluoroacaeamide and t-butyl carbamate. The selectivity in Diels-Alder cyclodaddition reaction with N-methyl maleimide was evaluated through single crystal X-ray analysis of the products. Models for the change in selectivity with hydrogen bond acceptor are proposed, supported by DFT level calculations.

9,10-Dihydroanthracenyl structures: original ligands for the synthesis of polymetallic complexes through selective π-coordination

N-Phenylsuccinimides and the corresponding pyrrolidines containing 9,10-dihydroanthracenyl skeletons were used for exploring their ability to coordinate RuCp(+) moieties through the aromatic rings. Electronic and steric tuning of ligands led to mono-, bi- and tri-metallic complexes. A full structural study was carried out in order to characterize the ruthenium organometallic compounds, proving the different coordination modes both in solution (NMR) and in solid state (X-ray diffraction). A modelling study (at DFT level) was completed with the aim to understand the selective π-coordination observed for mono- and bi-metallic complexes.

Ionic liquid promoted Diels-Alder Reaction between anthrone and maleimides

Ionic liquids (IL) are gaining importance as green solvents. Imidazolium ionic liquid [bmim]+[Cl]−, an environmentally benign solvent, was found to promote the Diels-Alder reaction between anthrone and maleimides at room temperature with excellent yields. The ionic liquid played a dual role as solvent and catalyst.

Enantioselective syntheses of candenatenins B and C using a chiral anthracene auxiliary

An asymmetric synthesis of two anticancer natural products, candenatenins B and C, is described, leading to a revision of the originally assigned stereochemistry. The synthesis follows a Diels-Alder/retro-Diels Alder strategy using a chiral anthracene auxiliary to access both targets with 90% ee. The inherent structural qualities of the auxiliary allow for both regio- and diastereoselective transformations.

Enantioselective synthesis of the R-enantiomer of the feeding deterrent (S)-ypaoamide

The enantioselective synthesis of the R-enantiomer of the marine natural product (S)-ypaoamide (5) is reported. The synthesis features both a flexible racemization-free approach to the 5-substituted 3-pyrrolin-2-one segment, and a lipase (CCL)-promoted deacetylation reaction to reach the orthogonal deprotection. Through this work the absolute configuration of the natural ypaoamide was determined as S.

Synthesis of alpha,beta-unsaturated gamma-lactams via asymmetric iridium-catalysed allylic substitution

Syntheses of alpha,beta-unsaturated gamma-lactams are described that are based on ring-closing metathesis in combination with enantioselective Ir-catalysed allylic amination using N-Boc-N-(but-2-enoyl)-amine as a pronucleophile. As an example application, the synthesis of a Baclofen analogue is presented.

Chiral Bicyclic Guanidine-Catalyzed Enantioselective Reactions of Anthrones

Chiral bicyclic guanidine 1 was found to be an excellent catalyst for reactions between anthrones and various dienophiles. The catalyst can tolerate a range of substituents and substitution patterns, making several anthrone derivatives suitable for this reaction. Both Diels-Alder and Michael adducts were obtained in excellent yields, high regioselectivities, and high enantioselectivities. This is the first case of a highly enantioselective base-catalyzed anthrone Diels-Alder reaction.

Highly diastereoselective Diels–Alder cycloadditions of 9R-(1-methoxyethyl)anthracene with p-benzoquinone

Diels-Alder cycloadditions of p-benzoquinone with 9R-(1-methoxyethyl)anthracene provides a 60:40 ratio of cycloadducts when heated at reflux in xylene. Mechanistic studies to explore the origins of this selectivity have shown that at lower temperatures the kinetic product predominates, giving a 96:4 ratio of cycloadducts.

N-Alkyl oxazolidines as stereocontrol elements in asymmetric Diels–Alder cycloadditions of 9-substituted anthracene derivatives

Chiral 9-oxazolidinyl anthracene derivatives have been prepared as single diastereoisomers by condensation of 9-anthraldehyde with the appropriate N-alkyl amino alcohol. Asymmetric Diels-Alder cycloadditions of these with N-methyl maleimide proceeds in good yield and in good diastereoselectivity, the sense of which may be controlled by judicious choice of the N-alkyl group.

Reactivity of cyclic sulfamidates towards sulfur-stabilised enolates. Stereocontrolled synthesis of functionalised lactams

A structurally representative series of 1,2- and 1,3-cyclic sulfamidates react with enolates derived from methyl alpha-phenylthioacetate 9b to give 5- and 6-substituted alpha-phenylthio lactams 20-24. These products provide, via the corresponding sulfoxides, an entry to alpha,beta-unsaturated lactams e.g. 12, 27, 29 and their alpha-phenylthio analogues e.g. 26 and 30. With the enantiomerically pure 1,2-cyclic sulfamidates 10, 15 and 17, these reactions all proceed with no detectable loss of stereochemical integrity.

Chiral anthracene and anthrone templates as stereocontrolling elements in Diels–Alder/retro Diels–Alder sequences

The development of chiral anthracene templates for use in Diels-Alder/retro Diels-Alder sequences is described. A summary of past results and new progress is reported.