Aromatic Β-ketoesters Research Articles

Improved synthesis of sterically encumbered heteroaromatic biaryls from aromatic β-keto esters

A protocol for the synthesis of hindered 4-aryl 2-aminopyrimidines from β–keto esters is described. The process employs trifluoroethanol as an essential additive to promote the guanidine condensation reaction, enabling the synthesis of 25 aryl- and heteroaryl substituted aminopyrimidines in good yields and high purities with no column chromatography. The conditions described herein are readily scalable and have been employed in the large-scale synthesis of the clinical A2a/A2bR antagonist AB928.

Photoredox Catalysis of Aromatic β-Ketoesters for in Situ Production of Transient and Persistent Radicals for Organic Transformation.

Radical formation is the initial step for conventional radical chemistry. Reported herein is a unified strategy to generate radicals in situ from aromatic β-ketoesters by using a photocatalyst. Under visible-light irradiation, a small amount of photocatalyst fac-Ir(ppy)3 generates a transient α-carbonyl radical and persistent ketyl radical in situ. In contrast to the well-established approaches, neither stoichiometric external oxidant nor reductant is required for this reaction. The synthetic utility is demonstrated by pinacol coupling of ketyl radicals and benzannulation of α-carbonyl radicals with alkynes to give a series of highly substituted 1-naphthols in good to excellent yields. The readily available photocatalyst, mild reaction conditions, broad substrate scope, and high functional-group tolerance make this reaction a useful synthetic tool.

One Pot Synthesis of Novel Substituted 2',4'-Dihydrospiro[chroman-2,3'-pyrazol]-4- one Derivatives

Aim and Objective: In the work, we have successfully presented a synthetic route for the synthesis of novel 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one derivatives via one pot multicomponent approach. Materials and Method: Substituted 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one were prepared through cascade three-component condensation of ortho-hydroxyacetophenone, β-ketoester, hydrazine in the presence of pyrrolidine as a catalyst under ethanol reflux conditions. Results: A series of novel 2',4'-dihydrospiro[chroman-2,3'-pyrazol]-4-one have been synthesized through a facile strategy. These structures of newly synthesized derivatives were determined by 1H, 13C NMR, HRMS and CHNS analysis. Conclusion: We have achieved the one-pot, three-component synthesis of highly substituted pyrazole spirochromanones in presence of pyrrolidine as a catalyst under ethanol reflux conditions. Using different types of aliphatic and aromatic β-ketoesters, o-hydroxyacetophenone derivatives and different kinds of hydrazine derivatives as building blocks, we could construct novel libraries of substituted pyrazole spirochromanones that make this method suitable for combinatorial and parallel synthesis in drug discovery.

Enantioselective hydrogenation of β-aryl-β-ketoester over α-hydroxy acid-modified Raney nickel catalysts: competitive hydrogenation with methyl acetoacetate

The enantioselective hydrogenation of the aromatic β-ketoesters, methyl 3-phenyl-3-oxypropanoate (1) and its p-methoxy-analogue (2), was studied over tartaric acid-modified Raney nickel catalysts. A competitive hydrogenation approach was used to clarify the catalytic behaviors of the enantio-differentiating hydrogenation of aromatic β-ketoesters over tartaric acid-modified Raney nickel, malic acid-modified Raney nickel, and unmodified Raney nickel in comparison with aliphatic one, represented by methyl acetoacetate. We found that the enantioselectivity could be elucidated by the interaction modes between the surface modifier, Ni metal surface, and the substrate as well as the keto/enol ratio of the substrate. We suggest that the moderate enantioselectivity of 1 over tartaric acid-modified Raney nickel is the result of distorted, weak two-point hydrogen bond interactions with surface tartrate due to unfavorable phenyl–Ni metal surface interactions. The p-methoxy group of 2 suppresses the phenyl–Ni metal surface interactions, resulting in an increase in the enantioselectivity of 2 over tartaric acid-modified Raney nickel. Ligand acceleration effects were observed with methyl acetoacetate and 2 but not with 1.

Synthesis of aromatic β-keto esters via a carbonylative Suzuki–Miyaura coupling reaction of α-iodo esters with arylboronic acids

Aromatic β-keto esters were synthesized via a carbonylative cross-coupling reaction of alkyl iodides and arylboronic acids in the presence of a catalytic amount of Pd catalyst.

Enantio-differentiating hydrogenation of aromatic β-ketoesters over tartaric acid-modified Raney nickel

The optical yields of the enantio-differentiating hydrogenation of aromatic β-ketoesters over tartaric acid-modified Raney nickel were found to be lower than those of aliphatic γ-ketoesters when the aromatic group is conjugated to the ketone moiety. The reason for the reduced optical yield is due to the lower intrinsic enantio-differentiation compared to the aliphatic substrate.

Simple and high yielding syntheses of β-keto esters catalysed by zeolites

Simple and high yielding syntheses of several β-keto esters, catalysed by zeolite Hβ are reported. The methods developed include condensation of aldehydes with ethyl diazoacetate and transesterification of β-keto esters with primary, secondary, allylic and benzylic alcohols etc., all catalysed by Hβ. It was further observed that under microwave irradiation the yields of many aromatic β-keto esters were enhanced appreciably.