Buchner Reaction Research Articles

Buchner and Beyond: Arene Cyclopropanation as Applied to Natural Product Total Synthesis

Buchner and Curtius first reported the cyclopropanation of arenes in 1885. Since the initial discovery, the Buchner reaction has been the subject of significant research by both physical and synthetic organic chemists. Described herein is a brief overview of the Buchner reaction and related arene cyclopropanation processes, with an emphasis on their application to natural product total synthesis.

Umpolung reactivity of indole through gold catalysis.

Umpolung reactivity of indole through gold catalysis.

Gold-catalyzed naphthalene functionalization

The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from N2C(R)CO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C–H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed.

Deactivation of Ru-benzylidene Grubbs catalysts active in olefin metathesis

In this work we explore the reactivity induced by coordination of a CO molecule trans to the Ru-benzylidene bond of a prototype Ru-olefin metathesis catalyst bearing the N-heterocyclic carbene (NHC) ligand SIMes. Static DFT calculations indicate that CO binding to the Ru center promotes a cascade of reactions with very low energy barriers that lead to the final crystallographically characterized product, in which the original benzylidene group has attacked the proximal aromatic ring of the SIMes ligand leading to a cycloheptatriene through a Buchner ring expansion. In conclusion, it consists of a carbene insertion into a mesityl group of the second generation Grubbs carbene complex. Instead of simply occupying open coordination sites, the ligand pushes the ruthenium-bound carbene into a position-selective cyclopropanation and rearrangement reaction manifold giving a cycloheptatriene ring, i.e. a Buchner reaction. The insertion may prove useful to identify carbene intermediates in enyne metathesis. Both carbon monoxide and isocyanides promote the cyclopropanation experimentally, that a computational analysis of the relevant molecular orbitals illuminates the key role of the π-acid CO coordinated trans to the Ru-benzylidene bond to promote this reactivity. Results clearly indicate that a π-acidic group, as CO, that can approach the Ru center in the sterically crowded position trans to the Ru-benzylidene bond can promote this deactivation route.

Enhancement of Enantioselection in the Copper-Catalysed Intramolecular Büchner Reaction by Variation of the Counterion

In the advanced online (e-First) publication of this manuscript, the Büchner reaction was misspelled as Buchner reaction throughout the manuscript. It has been corrected for both the print and the current online versions.

Enhancement of Enantioselection in the Copper-Catalysed Intramolecular Büchner Reaction by Variation of the Counterion

Variation of the enantioselection of the copper-catalysed intramolecular Buchner reaction of diazoketones with the nature of the counterion is reported; significantly the presence of the non-coordinating BARF anion leads to enhanced enantioselectivities when the aryl group bears electron-withdrawing halo substituents.

Facile synthesis of 2-azaazulenes from thiobenzoyl isocyanates using trimethylsilyldiazomethane

The reaction of trimethylsilyldiazomethane with thiobenzoyl isocyanates, in situ generated from thiazole-4,5-diones, yielded diazoketones, which were converted into 2-azaazulenes by the intramolecular Buchner reaction.

Enantioselective Intramolecular Büchner Reaction of α-Diazoketones

Enantioselectivities of up to 95% ee have been achieved in the intramolecular Buchner reaction catalysed by copper bis(ox-azoline) complexes, the highest asymmetric inductions reported to date for this transformation. Significantly, use of a catalyst derived from a bis(oxazoline) ligand resulted in high enantioselectivities across several substrates, indicating the possibility of developing a catalyst with general applicability.

Carbon Monoxide-Promoted Carbene Insertion into the Aryl Substituent of an N-Heterocyclic Carbene Ligand: Buchner Reaction in a Ruthenium Carbene Complex

In the presence of carbon monoxide, ruthenium carbenes give a net insertion/ring expansion (Buchner reaction) into one of the aromatic rings of the N-heterocyclic carbene ligand. In alkene metathesis applications, the N-heterocyclic carbene ligand is both robust and typically inert to reactions with the metal-bound carbene. This unique reaction is completely regioselective. The complexes obtained through ring expansion were fully characterized in the solid state using X-ray crystallography and in solution using NMR and IR spectroscopy.

Preparation of Methoxy‐Substituted Optically Active 7‐Alkoxycarbonylcycloheptatrienes and Their Acid‐Promoted Rearrangements.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ring Expansion-Annulation Strategy for the Synthesis of Substituted Azulenes and Oligoazulenes. 2. Synthesis of Azulenyl Halides, Sulfonates, and Azulenylmetal Compounds and Their Application in Transition-Metal-Mediated Coupling Reactions

A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by beta-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.

Chemoselectivity and enantiocontrol in catalytic intramolecular metal carbene reactions of diazo acetates linked to reactive functional groups by naphthalene-1,8-dimethanol

The use of chiral dirhodium(II) carboxamidate catalysts for metal carbene transformations of diazo acetates linked to a reactive functionality through naphthalene-1,8-dimethanol produces chemoselective and enantioselective reaction either at the remote functionality or by addition to the 1,2-position of the naphthalene ring; enantioselectivities up to 84% ee have been obtained for the Buchner reaction.

Stereocontrol in the intramolecular Buchner reaction of diazoamides and diazoesters

Dirhodium(II) catalysed decomposition of diazoamide 5 resulted in formation of β-lactams 6/7 by intramolecular C–H insertion, the intramolecular Buchner reaction being disfavoured for conformational reasons. The diazoamide 8, however, gave products resulting from both the intramolecular Buchner reaction and C–H insertion. Chiral diazoesters 14–16 derived from α-substituted benzyl alcohols gave cycloheptatrienes in a highly diastereoselective manner; the norcaradiene isomer of the cycloheptatrienes was readily intercepted in a Diels–Alder reaction with 4-phenyl-1,2,4-triazoline-3,5-dione to give adducts 19–21.

Rhodium(II)-Catalyzed Decomposition of 1-Diazo-4-(1- or 2-naphthyl)-2-butanones as a New Route to Rearranged Pimarane and Abietane Skeleta. Synthesis of Umbrosone

The Rh2(OAc)4-catalyzed intramolecular Buchner reaction of 1-diazo-4-(1- or 2-naphthyl)butan-2-ones was examined as a potential route to abietane and rearranged abietane derivatives. Treatment of the α-diazo ketone 26 with catalytic amount of dirhodium tetraacetate in CH2Cl2 at 0 °C furnished the tetracyclic derivative 27 in good yield. Addition of TFA to 27 (in CH2Cl2) resulted in an acid-induced opening of the cyclopropane ring to give the 4a- and 10a-methyldihydrophenanthrenones 28 and 29 in nearly equal amounts. These compounds and their analogs appear to be suitable intermediates for the synthesis of diterpenoids containing aromatic A or C rings. When the diazo ketone 34 was decomposed under Rh(II) catalysis, a 10-methyldihydroanthracenone (i.e., 36) was obtained as the main product, besides minor amounts of the expected tetracyclic ketone 35. The extension of this result to the preparation of the methoxy-substituted dihydroanthracenone 39 (52% yield) was exploited in a new total synthesis of umbroso...

A reinvestigation of the intramolecular Buchner reaction of 1-diazo-4-phenylbutan-2-ones leading to 2-tetralones

Rhodium acetate-catalysed decomposition of 1-diazo-4-(2-methoxyphenyl)butan-2-one 8 leads, after rearrangement under acidic conditions, to 5-methoxy-2-tetralone 13 and not to 8-methoxy-2tetralone 10 as reported.

The intramolecular Buchner reaction of aryl diazoketones. Synthesis and X-ray crystal structures of some polyfunctional hydroazulene lactones

The feasibility of constructing polyfunctional hydroazulenes bearing fused lactone rings via rhodium(II)-catalysed cyclisation of suitably constituted diazoketones followed by catalytic hydrogenation has been examined with respect to both direction and efficiency of cyclisation. The presence of the lactone on the aromatic precursor influences the direction of cyclisation as do substituents at the α-position on the lactone ring. Sulphur-containing substituents inhibit cyclisation. Several new unnatural hydroazulene lactones have been produced. The stereochemistry of hydrogenation of the cyclisation products in two cases has been determined by X-ray diffraction and NMR analysis. Crystals of lactone (34) are monoclinic, space group P21/a, in a cell of dimensions a= 8.625(2), b= 12.993(4), c= 12.109(2)A, β= 105.79(1)°. Crystals of lactone (42) are monoclinic, space group P21/c, in a cell of dimensions a= 12.885(2), b= 6.115(4), c= 19.417(4)A, β= 107.14(1)°. The structures were solved by direct methods and refined by full-matrix least-squares calculations; for (34), R= 0.047 for 1405 reflections with l > 3σ(I); for (42), R= 0.045 for 1 370 reflections with I > 3σ(I). The crystal structures establish the relative stereochemistry of hydrogenation of the unsaturated lactones and confirm the direction of cyclisation of the ketocarbenoid intermediates.

The intramolecular Buchner reaction of aryl diazoketones. Substituent effects and scope in synthesis

Rhodium(II) acetate-catalysed cyclisation of α-diazoketones derived from 3-arylpropionic acid produces bicyclo[5.3.0]decatrienones or 2-tetralones depending on the substitution pattern of the aryl ring in the precursor; the former products are transformed into the latter catalytically with trifluoroacetic acid. Precursors with methyl, methoxy, and acetoxy substituents have been examined, efficient cyclisation occurring in all cases. When the precursor contains a meta-methoxy substituent, 2-tetralones are obtained directly. The efficient conversion of 3-phenylpropionic acid into trans-1-methylbicyclo[5.3.0]decan-2-one is also described, partial asymmetric synthesis having been realised through the use of rhodium (S)-mandelate as the cyclisation catalyst. Cyclisations of diazoketones derived from 4-phenylbutyric acid and 5-phenylpentanoic acid have also been studied; the former provides a new entry into the bicyclo[5.4.0]undecane system whereas the latter produces a 2,3-disubstituted cyclopentanone via C–H insertion. Aspects of the cycloheptatriene-norcaradiene equilibrium in fused ring systems are discussed.

Catalytic control of reactions of dipoles and carbenes; an easy and efficient synthesis of cycloheptatrienes from aromatic compounds by an extension of Buchner's reaction

Rhodium salts from strong carboxylic acids [particularly rhodium(II) trifluoroacetate] are novel and highly efficient catalysts for the preparation of substituted cycloheptatriene carboxylates from aromatic hydrocarbons and diazo-esters, and in contrast with the classical Buchner procedures these rhodium catalysts lead specifically to the 1-isomer (3), avoiding its subsequent prototropic conversion into conjugated isomers.