Isomerization of 7-Oxabenzonorbornadienes into Naphthols Catalyzed by [RuCl2(CO)3]2

Reactive Processing of Furan-Based Monomers via Frontal Ring-Opening Metathesis Polymerization for High Performance Materials

Frontal ring-opening metathesis polymerization (FROMP) presents an energy-efficient approach to produce high-performance polymers, typically utilizing norbornene derivatives from Diels-Alder reactions. This study broadens the monomer repertoire for FROMP, incorporating the cycloaddition product of biosourced furan compounds and benzyne, namely 1,4-dihydro-1,4-epoxynaphthalene (HEN) derivatives. A computational screening of Diels-Alder products is conducted, selecting products with resistance to retro-Diels-Alder but also sufficient ring strain to facilitate FROMP. The experiments reveal that varying substituents both modulate the FROMP kinetics and enable the creation of thermoplastic materials characterized by different thermomechanical properties. Moreover, HEN-based crosslinkers are designed to enhance the resulting thermomechanical properties at high temperatures (>200 °C). The versatility of such materials is demonstrated through direct ink writing (DIW) to rapidly produce 3D structures without the need for printed supports. This research significantly extends the range of monomers suitable for FROMP, furthering efficient production of high-performance polymeric materials.

Access to Naphthoic Acid Derivatives through an Oxabenzonorbornadiene Rearrangement

Herein, the synthesis of 1-hydroxy-2-naphthoic acid esters through an unexpected Lewis-acid-mediated 1,2-acyl shift of oxabenzonorbornadienes is reported. Using this methodology, novel substitution patterns for 1-hydroxy-2-naphtoic acid esters can be obtained. A mechanistic proposal and rationale for this transformation, the products of which had been previously incorrectly characterized, is given.

Iridium-catalyzed hydroacylation reactions of C1-substituted oxabenzonorbornadienes with salicylaldehyde: an experimental and computational study

An experimental and theoretical investigation on the iridium-catalyzed hydroacylation of C₁-substituted oxabenzonorbornadienes with salicylaldehyde is reported. Utilizing commercially available [Ir(COD)Cl]₂ in the presence of 5 M KOH in dioxane at 65 °C, provided a variety of hydroacylated bicyclic adducts in up to a 95% yield with complete stereo- and regioselectivity. The mechanism and origins of selectivity in the iridium-catalyzed hydroacylation reaction has been examined at the M06/Def2TZVP level of theory. The catalytic cycle consists of three key steps including oxidative addition into the aldehyde C–H bond, insertion of the olefin into the iridium hydride, and C–C bond-forming reductive elimination. Computational results indicate the origin of regioselectivity is involved in the reductive elimination step.

Palladium-Catalyzed Rearrangement Reaction to Access 1-Phenanthrol Derivatives

This manuscript describes an unusual Pd-catalyzed rearrangement reaction. It provides efficient access to 1-phenanthrol derivatives using allyloxy-tethered aryl iodides. This rearrangement process involves the cleavage of C-I bond, C-O bond...

Recent Advances on Diels-Alder-Driven Preparation of Bio-Based Aromatics

The preparation of high value-added chemicals from renewable resources is a crucial approach towards a sustainable economy. One prominent alternative to the production of petroleum-based chemicals from fossil resources is through the sequential Diels-Alder/aromatization reactions of biomass-derived furan platforms. This Concept is focused on the recent boom in bio-based furan DA strategies for aromatization of bio-based platform chemicals, particularly that of furfurals, ranging from indirect use and activation strategies to recent examples of direct DA reaction of these electron-withdrawing biomass-derived furans.

Size-Driven Inversion of Selectivity in Esterification Reactions: Secondary Beat Primary Alcohols

Relative rates for the Lewis base-mediated acylation of secondary and primary alcohols carrying large aromatic side chains with anhydrides differing in size and electronic structure have been measured. While primary alcohols react faster than secondary ones in transformations with monosubstituted benzoic anhydride derivatives, relative reactivities are inverted in reactions with sterically biased 1-naphthyl anhydrides. Further analysis of reaction rates shows that increasing substrate size leads to an actual acceleration of the acylation process, the effect being larger for secondary as compared to primary alcohols. Computational results indicate that acylation rates are guided by noncovalent interactions (NCIs) between the catalyst ring system and the DED substituents in the alcohol and anhydride reactants. Thereby stronger NCIs are formed for secondary alcohols than for primary alcohols.

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes

Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate, which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers, which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

[(1R*,3S*,4S*)-3-(2-Hydroxybenzoyl)-1,2,3,4-tetrahydro-1,4-epoxynaphthalen-1-yl]methyl 4-nitrobenzoate

The relative stereo- and regiochemistry of the title compound, C₂₅H₁₉O₇N, were determined by the X-ray analysis.

The relative stereo- and regiochemistry of the racemic title compound, C₂₅H₁₉NO₇, were established from the crystal structure. The fused benzene ring forms dihedral angles of 77.3 (1) and 60.3 (1)° with the hy­droxy-substituted benzene ring and the nitro-substituted benzene ring, respectively. The dihedral angle between the hy­droxy-substituted benzene ring and the nitro-substituted benzene ring is 76.4 (1)°. An intra­molecular O—H⋯O hydrogen bond closes an S(6) ring. In the crystal, weak C—H⋯O hydrogen bonds connect the mol­ecules, forming layers parallel to (100). Within these layers, there are weak π–π stacking inter­actions with a ring centroid–ring centroid distance of 3.555 (1) Å.

Transition metal-catalyzed coupling of heterocyclic alkenes via C–H functionalization: recent trends and applications

Heterocyclic alkenes and their derivatives are an important class of reactive feedstock and valuable synthons. This review highlights the transition-metal-catalyzed coupling of heterocyclic alkenes via a C–H functionalization strategy.

One-pot generation of benzynes from 2-aminophenylboronates via a Rh(ii)-catalyzed N–H amination/oxidation/elimination cascade process

Rh(ii)-Nitrene-mediated N–H amination of 2-aminophenylboronates triggered a cascade of oxidation/elimination processes resulting in the generation of benzynes.

Palladium-Catalyzed syn-Stereocontrolled Ring Opening of Oxabicyclic Alkenes with Arylsulfonyl Hydrazides

A novel palladium-catalyzed ring-opening reaction of oxabicyclic alkenes with arylsulfonyl hydrazides was first developed. In this work, we provide an efficient one-pot reaction to afford the corresponding cis-2-aryl-1,2-dihydronaphthalen-1-ols and 2-aryl-naphthalenes in moderate to excellent yields (up to 95%) under an open-air condition. Various types of functional groups attached to the substrates were tolerated well in this method. Among them, the cis-1,2-configuration of product 3ag was confirmed by X-ray crystallographic analysis. In addition, a plausible mechanism for ring opening was also proposed.

Three-Component Cycloaddition To Synthesize Aziridines and 1,2,3-Triazolines

An efficient three-component cycloaddition of oxa(aza)bicyclic alkenes/norbornene in the presence of NaN₃ and arylsulfonyl chlorides was developed, affording the corresponding aziridine products in good yields (up to 82%) with moderate to good endo/exo selectivities (up to >99:1 endo/exo). Further studies showed that the cycloaddition of oxa(aza)bicyclic alkenes in the presence of NaN₃ and chloroalkanes could afford the exo-cycloadduct 1,2,3-triazolines in good to excellent yields (up to 95%). Compared with the existing methodologies, the current protocol demands very simple and mild reaction conditions and is a metal-free catalyzed reaction. In addition, a plausible mechanism for the cycloaddition reaction was also proposed.

Palladium/Lewis Acid Cocatalyzed Ring-Opening Reactions of Unsymmetrical Oxabenzonobornadienes with Oximes

The palladium/Lewis acid cocatalyzed ring-opening reaction of various C₁-substituted unsymmetrical oxabenzonorbornadienes (OBD) with oxime nucleophiles was investigated. The effects of various C₁ substituents were explored. Moderate to excellent yields and excellent regioselectivities were obtained for electron-withdrawing groups. The presence of electron-donating alkyl groups leads to isomerization of the corresponding OBD to afford the substituted naphthol derivatives. Additionally, a mechanism for the formation of C₂ regioisomeric ring-opened products has been proposed.

1-[(1R*,2R*)-1,2-Dihydroxy-1,2-dihydronaphthalen-1-yl]ethan-1-one

The crystal structure of the centrosymmetic title compound, C12H12O3, confirms the relative stereochemistry. The 1,2-dihydrobenzene ring is in a flattened half-chair conformation. In the crystal, O—H...O hydrogen bonds link the molecules into layers lying parallel to (001).

Regioselective arene homologation through rhenium-catalyzed deoxygenative aromatization of 7-oxabicyclo[2.2.1]hepta-2,5-dienes

A facile approach to PAHs with an arm-chair edge via regioselective bromination, Diels–Alder reaction, and rhenium-catalyzed deoxygenative aromatization is described.

Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl₂(CH₃CN)₂ in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases.

Synthetic transformation of 1,3-diarylisobenzofuran-DMAD adducts: a facile preparation of tri-substituted α-naphthols

1,3-Diarylisobenzofuran-DMAD adducts upon reaction with BF₃·OEt₂ in DCM at room temperature underwent a regiospecific 1,2-aryl migration followed by the Krapcho decarboxylation to give tri-substituted α-naphthols in good yields.

Iridium-Catalyzed Asymmetric Ring-Opening of Oxabenzonorbornadienes with N-Substituted Piperazine Nucleophiles

Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]₂ and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i.

Syntheses of arnottin I and arnottin II

Short total syntheses of arnottin I and II were accomplished in 5 and 6 steps, respectively. A sesamol-benzyne cycloaddition with a 3-furyl-benzoate followed by regiospecific lactonization provided rapid, large-scale access to the core of arnottin I. Saponification of arnottin I and hypervalent iodide mediated spirocyclization provided an efficient and direct preparation of racemic arnottin II.

A new synthetic route to substituted tetracenes and pentacenes via stereoselective [4+2] cycloadditions of 1,4-dihydro-1,4-epoxynaphthalene and isobenzofuran

Substituted tetracene and pentacene were efficiently prepared by stereoselective [4+2] cycloadditions of 1,4-dihydro-1,4-epoxynaphthalenes and isobenzofurans.

Synthesis and evaluation of 9-deoxy analogues of (-)-thysanone, an inhibitor of HRV 3C protease

9-Deoxy analogues of the HRV 3C protease inhibitor (-)-thysanone display better inhibitory properties than the natural product, inferring the C9-OH hinders binding to the enzyme.

Platinum-catalyzed anti-stereocontrolled ring-opening of oxabicyclic alkenes with Grignard reagents

A new platinum-catalyzed anti-stereocontrolled ring-opening of oxabicyclic alkenes with various Grignard reagents was reported, which afforded the corresponding anti-2-substituted-1,2-dihydronaphthalen-1-ol products with moderate to good yields in the presence of a catalytic amount of Pt(PPh3)4 (2.5 mol%) under mild conditions. The effects of catalyst loading, solvent and temperature on the yield were also investigated. Furthermore, the trans-configuration of the product 5i was confirmed by X-ray diffraction analysis.

Tetra-tert-butyl 13,14-dioxapentacyclo[8.2.1.14,7.02,9.03,8]tetradeca-5,11-diene-5,6,11,12-tetracarboxylate

The stereochemistry of the title compound, C₃₂H₄₄O₁₀, at the cyclo­butane ring is cis-anti-cis. The mol­ecule lies across an inversion center. In the crystal, weak C—H⋯O hydrogen bonds connect mol­ecules into chains along [100], forming R₂²(6) rings.

Tetramethyl 1,4-dimethyl-13,14-dioxapentacyclo[8.2.1.14,7.02,9.03,8]tetradeca-5,11-diene-5,6,11,12-tetracarboxylate

In the title compound, C₂₂H₂₄O₁₄, the relative stereochemistry at the cyclo­butane ring is cis-anti-cis and the methyl groups in the bicyclic rings are syn to each other. The two carboxyl­ate groups attached to the same —C=C— bond are disordered over two sets of sites in a 0.603 (2):0.397 (2) ratio. In the crystal, weak C—H⋯O hydrogen bonds connect mol­ecules into C(12) chains along [001] incorporating R₂²₂(10) rings.

Hexamethyl 13,14-dioxapentacyclo[8.2.1.14,7.02,9.03,8]tetradeca-5,11-diene-1,4,5,6,11,12-hexacarboxylate

In the title compound, C₂₄H₂₄O₁₄, the stereochemistry at the cyclo­butane ring is cis-anti-cis and the –COOMe groups in the bicyclic rings are syn to each other. The mol­ecule lies on a twofold rotation axis. In the crystal, weak C—H⋯O hydrogen bonds connect mol­ecules into chains along [001], forming R₂²(10) rings.