Vinylogous Position Research Articles

Synthesis of Heterocycles by HNTf2-Catalyzed C–H Functionalization of Vinyldiazo Compounds with 3-Phenyl-3-hydroxyisoindolinone

AbstractA Brønsted acid catalyzed C–H functionalization of vinyldiazoacetates with 3-hydroxyisoindolinone is developed. This methodology provides a general access to E-substituted isoindolinone vinyldiazo compounds in good yields and excellent diastereoselectivities with broad substrate generality under mild conditions, and with 4-substituted 2-diazo-3-butenoates produces fused bicyclic pyrrolidines. The reaction generally involves addition of the N-acyl ketiminium electrophile, formed from the 3-hydroxyisoindolinone, to the vinylogous position of the vinyldiazo compound resulting in vinyldiazonium ion intermediates that undergo deprotonation to new vinyldiazo compounds or ring closure to fused bicyclic pyrrolidines.

HNTf2-Catalyzed Formal [3 + 2] Cycloaddition of Vinyldiazoacetates to Indole-Substituted Diazo Compounds and Their Conversion to Carbazoles.

Triflimide catalysis of the [3 + 2]-cycloaddition of 3-indolymethanols with vinyldiazoacetates provides general access to β-tetrahydrocyclopenta[b]indol-substituted α-diazoesters. Initiated by addition of the in situ generated vinylogous iminium electrophile from 3-indolymethanol to the vinylogous position of the vinyldiazo compound and completed by intramolecular cyclization from the vinyldiazonium ion intermediate, this transformation occurs in good yields and excellent diastereoselectivity with a broad substrate scope under mild conditions. The resulting α-diazoesters undergo Rh2(OAc)4-catalyzed substrate-dependent 1,2-migration to form multisubstituted carbazoles in high yields.

Rhodium(I)-Catalyzed Direct Enantioselective C-H Functionalization of Indoles.

A highly regiospecific vinylogous carbene insertion protocol for direct asymmetric C-H functionalization of indoles with arylvinyldiazoacetates has been developed. Under the catalysis of simple Rh(I)/chiral diene complexes, the reaction occurs solely at the vinylogous position of the vinylcarbenoid with exceptional E selectivity and enantiocontrol. It provides an efficient way to obtain an interesting class of chiral indole scaffolds bearing an α,β-unsaturated ester unit and a gem-diaryl carbon stereocenter in good yields (≤99%) with excellent enantioselectivities (≤96%) at room temperature.

Intramolecular Interception of the Remote Position of Vinylcarbene Silver Complex Intermediates by C(sp3 )-H Bond Insertion.

The trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp3 )-H bond has been achieved for the first time during a silver-catalyzed carbene/alkyne metathesis (CAM) process. A Tpx -containing silver complex first promotes the generation of a donor-acceptor silver carbene which triggers CAM, generating a subsequent donor-donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp3 )-H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C-H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step.

Intramolecular Interception of the Remote Position of Vinylcarbene Silver Complex Intermediates by C(sp3)−H Bond Insertion

AbstractThe trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp3)−H bond has been achieved for the first time during a silver‐catalyzed carbene/alkyne metathesis (CAM) process. A Tpx‐containing silver complex first promotes the generation of a donor‐acceptor silver carbene which triggers CAM, generating a subsequent donor‐donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp3)−H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C−H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step.

Intermolecular [5 + 1]-Cycloaddition between Vinyl Diazo Compounds and tert-Butyl Nitrite to 1,2,3-Triazine 1-Oxides and Their Further Transformation to Isoxazoles.

1,2,3-Triazine 1-oxides are formed by nitrosyl addition from tert-butyl nitrite to the vinylogous position of vinyl diazo compounds. This transformation, which is a formal intermolecular [5 + 1] cycloaddition, occurs under mild conditions, with high functional group tolerance and regioselectivity, and can be employed for late-stage functionalization. Upon heating at refluxing chlorobenzene temperature, these triazine-N-oxides undergo dinitrogen extrusion to form isoxazoles in very high yields.

Enantioselective Gold(I)-Catalyzed Vinylogous [3 + 2] Cycloaddition between Vinyldiazoacetates and Enol Ethers

The reaction of vinyldiazoacetates with enol ethers catalyzed by the binuclear gold complex (R)-DTBMSegphos(AuCl)2 activated by silver hexafluoroantimonate results in a highly enantioselective [3 + 2] cycloaddition. The [3 + 2] cycloaddition proceeds with dynamic kinetic resolution when the enol ether is a 4-substituted 1-(methoxymethylene)cyclohexane. The reaction is initiated by nucleophilic attack of the vinyl ethers at the vinylogous position of the gold vinylcarbene intermediate.

ChemInform Abstract: Alkynoate Synthesis Through the Vinylogous Reactivity of Rhodium(II) Carbenoids.

Siloxy group migration: A rhodium(II) carbenoid approach has been developed for the synthesis of alkynoates. This transformation combines the addition of enol ethers at the vinylogous position of β-siloxy-substituted vinyldiazo derivatives with a siloxy group migration to give the products as single diastereomers.

Alkynoate synthesis through the vinylogous reactivity of rhodium(II) carbenoids.

Siloxy group migration: A rhodium(II) carbenoid approach has been developed for the synthesis of alkynoates. This transformation combines the addition of enol ethers at the vinylogous position of β-siloxy-substituted vinyldiazo derivatives with a siloxy group migration to give the products as single diastereomers.

Rh2(S-biTISP)2-Catalyzed Asymmetric Functionalization of Indoles and Pyrroles with Vinylcarbenoids

Asymmetric functionalization of N-heterocycles by vinylcarbenoids in the presence of catalytic amounts of Rh(2)(S-biTISP)(2) has been successfully developed. This bridged dirhodium catalyst not only selectively enforces the reaction to occur at the vinylogous position of the carbenoid but also affords high levels of asymmetric induction.

Convenient method for the functionalization of the 4- and 6-positions of the androgen skeleton.

The preparation and reactivity of steroidal vinyldiazo compounds is reported, providing a convenient, substituent tolerant, chemo- and stereoselective entry into 4- and 6-substituted androgen analogues from a common precursor. Under dirhodium catalysis, O-H insertion occurs at the carbenoid site, leading to 4-substituted steroids, but under silver catalysis, O-H insertion occurs at the vinylogous position, leading to 6-substituted steroids.

Rhodium carbenoid approach for introduction of 4-substituted (Z)-pent-2-enoates into sterically encumbered pyrroles and indoles.

An unusual rhodium carbenoid approach for introduction of 4-substituted (Z)-pent-2-enoates into sterically encumbered pyrroles and indoles is described. These studies show that (Z)-vinylcarbenoids have a greater tendency than (E)-vinylcarbenoids to react at the vinylogous position of the carbenoid rather than at the carbenoid center.

Diradical‐Promoted Two‐Carbon Ring‐Expansion Reactions by Thermal Isomerization: Synthesis of Functionalized Macrocyclic Ketones

AbstractA new method for the smooth and highly efficient preparation of functionalized macrocyclic ketones has been developed. Pyrolysis of medium‐ and large‐ring 3‐vinylcycloalkanones by dynamic gas‐phase thermo‐isomerization (DGPTI) at 600–630° yielded, under insertion of a previously attached vinyl side chain by means of a 1,3‐C shift, the corresponding γ,δ‐unsaturated cycloalkanones. The yield of the two‐carbon ring‐expanded ketones greatly depended on the relative ring strains of substrate and product (5–87%, cf. Table 5). The formation of minor amounts of one‐carbon ring‐expanded cycloalkenes (<10%) can be ascribed to a subsequent decarbonylation step. A reaction mechanism involving initial cleavage of the weakest single bond in the molecule has been established (cf. Scheme 6). Recombination within the generated diradical intermediate in terminal vinylogous position led to the observed products, while reclosure gave recovered starting material. Substituents on the vinyl moiety were transferred locospecifically into the ring‐expanded products. An isopropenyl group did not significantly affect the isomerization process, whereas substrates bearing a prop‐1‐enyl group in β‐position enabled competing intramolecular H‐abstraction reactions, leading to acyclic dienones (cf. Schemes 9–11). DGPTI of the 13‐membered analogue directly yielded 4‐muscenone, which, upon hydrogenation, led to the valuable musk odorant (±)‐muscone. Increasing the steric hindrance on the vinyl moiety gave rise to diminishing amounts of the desired γ,δ‐unsaturated cycloalkanones. This novel two‐carbon ring‐expansion protocol was also successfully applied to 3‐ethynylcycloalkanones, giving rise to the corresponding ring‐expanded cyclic allenes (cf. Scheme 13).

Aza-enamines X:Formylation of Pyrazole-4-carbaldehydeHydrazones at the Hydrazonoazomethine C-Atom

1,3-Disubstituted 1H-pyrazole-4-carbaldehyde-N,N-di-methylhydrazones 1 reacted with the Vilsmeier-Haack reagent, corresponding to the aza-enamine concept, in an electrophilic substitution reaction at the azomethine C-atomyielding the 1,4,5-triaza-pentadienium salts 2. These were hydrolysed to give 2-hydrazono-2-( 1H-pyrazole-4-yl)ethanals 3. The electrophilic attack did not take place at the vinylogous position 5' of the pyrazoles.

Regiochemistry of molybdenum-catalyzed O–H insertions of vinylcarbenoids

Molybdenum-catalyzed decomposition of vinyldiazoacetates generates vinylcarbenoids that preferentially react with alcohols at the vinylogous position of the vinylcarbenoid rather than at the carbenoid site.

Carbenoid versus Vinylogous Reactivity in Rhodium(II)-Stabilized Vinylcarbenoids

Rhodium(II)-stabilized vinylcarbenoid intermediates display electrophilic character at both the carbenoid site and the vinylogous position. The solvent and catalyst as well as the vinylcarbenoid structure have major effects on the regiochemical outcome of the reaction of vinylcarbenoids with alkenes and dienes. Reaction of vinylcarbenoids with vinyl ethers can lead to the formation of either cyclopropanes or cyclopentenes while reaction of vinylcarbenoids with cyclopentadiene can lead to the formation of either bicyclo[3.2.1]octadiene or bicyclo[2.2. 1]heptene derivatives

Pteridines XCVIII. Synthesis and Properties of 1-Methylpterins

SummaryA series of 1-methyl-pterin derivatives (6-13) have been synthesized by condensation and methylation reactions. The compounds have been characterized by elemental analyses, pKa deterimations and UV spectra. Comparisons of the physical data of the corresponding N-1 and N-3 methyl-pterins indicate why the normal pterins exist in aqueous solution preferentially in the N3-H tautomeric configuration. The thermodynamical stability of the lactam group forces the acidic H-atom to adapt the nitrogen adjacent to the carhonyl function but no other vinylogous position. A lactam group does not participate in heteroaromatic cyclic resonance, in general.

Anomalous reactivity of mono substituted rhodium stabilized vinylcarbenoids

In contrast to rhodium(lI) stabilized vinylcarbenoids with two electron withdrawing groups, the related mono substituted vinylcarbenoids exhibit reactivity at either the carbenoid center or the vinylogous position. The site of reactivity may be controlled by appropriate catalysts and solvents, leading to the effective synthesis of bicyclic systems by a tandem cyclopropanation/Cope rearrangement sequence.

The E1cb route for ester hydrolysis; volumes of activation as an additional criterion of mechanism

Hydrolyses of esters which possess an acidic proton at the α or vinylogous position can, in principle, hydrolyse by the E1cb route via a ketenoid intermediate. To the kinetic evidence for such a mechanism in the hydrolyses of 4-hydroxybenzoates, malonates, acetoacetates and fluorenecarboxylates is now added the further criterion of volumes of activation. Values of ΔV‡ for reactions proceeding by the E1cb route are positive and contrast with the negative values associated with hydrolyses by the more usual BAc2 mechanism.