Synthesis of vinyl 1,2-diketones

A new route is outlined for preparation of vinyl 1,2-diketones via a three-step sequence. First, allylic alcohols are photooxidized by ¹O₂ to hydroperoxides, which are reduced to vinyl 1,2-diols. These vinyl 1,2-diols are oxidized to vinyl 1,2-diketones with oxoammonium salts, which are prepared in situ from organic nitroxyl radicals. The new route is short, avoids the use of protecting groups, and is generally applicable to obtain aliphatic or aromatic vinyl 1,2-diketones.     

Ring-opening of tertiary cyclopropanols derived from β-diketones

The ring-opening reaction of 1,2-disubstituted cyclopropanols, prepared from β-diketones, mediated by Cu(NO₃)₂, p-TsOH, and NaOH is reported. The Cu(II)-mediated ring-opening of cyclopropanols gave α-methylene-γ-diketones in good yields. The reaction took place at the less substituted carbon of the cyclopropanols, involving mild conditions and a simple procedure. The reaction induced by p-TsOH in CH₂Cl₂ afforded α-methyl-γ-diketones as the major product with minor amounts of δ-diketones. The 2,3,5-trisubstituted furans were obtained in high yields when the ring-opening reaction was mediated by p-TsOH in methanol under reflux conditions. In the presence of sodium hydroxide the reaction proceeded smoothly in preference to the formation of δ-diketones, particularly for substrates with an aromatic group on the cyclopropane.     

Zinc-mediated chain extension reaction of 1,3-diketones to 1,4-diketones and diastereoselective synthesis of trans-1,2-disubstituted cyclopropanols

[reaction: see text] A variety of 1,3-diketones can be efficiently converted into the corresponding 1,4-diketones and trans-1,2-disubstituted cyclopropanols by using organozinc species in one-pot reactions. It was found that 2.3 equiv of CF3CO2ZnCH2I was effective to give the corresponding chain-extended products in 44-85% yields, while a mixture of organozinc species formed from 4.0 equiv of Et2Zn, 2.0 equiv of CF3CO2H, and 4.0 equiv of CH2I2 resulted in the formation of trans-1,2-disubstituted cyclopropanols with quite good yields and diastereoselectivity.     

Photoaddition reactions of 1,2-diketones with silyl ketene acetals. formation of beta-hydroxy-gamma-ketoesters

Photochemical reactions taking place between 1,2-diketones and silyl ketene acetals and their excited state reaction mechanisms have been explored. Irradiation of benzene, acetone, or acetonitrile solutions containing 1,2-diketones and silyl ketene acetals is observed to promote formation of 1,4-dioxenes, resulting from [4 + 2]-cycloaddition, oxetanes, arising by Paterno-Buchi processes, and beta-hydroxy-gamma-ketoesters, generated by SET-promoted Claisen-type condensation. These competitive pathways leading from the excited states of the 1,2-diketones to these products are influenced by solvent polarity and the nature of the silyl ketene acetal and 1,2-diketone. The Claisen-type condensation process, following an SET desilylation pathway and predominating when the photoreactions are carried out in the polar solvent acetonitrile, represents an efficient method to prepare a variety of diversely substituted beta-hydoxy-gamma-ketoesters.     

A highly efficient ruthenium-catalyzed rearrangement of alpha,beta-epoxyketones to 1,2-diketones

TpRuPPh(3)(CH(3)CN)(2)PF(6) catalyzed the efficient rearrangement of alpha,beta-epoxyketones to 1,2-diketones. Unlike a previously reported iron catalyst, the reaction in this case is applicable not only to 1,2-disubstituted epoxides but also to mono- and trisubstituted epoxides and tolerates oxygen functionalities. The sterically crowded and highly basic tris(1-pyrazolyl)borate (Tp) ligand of the ruthenium catalyst might account for its high selectivity toward 1,2-diketone rather than 1,3-diketone.     

Asymmetric direct aldol reaction of 1,2-diketones and ketones mediated by proline derivatives

The direct aldol reaction of 1,2-diketones and ketones mediated by proline derivatives yields the corresponding 2-hydroxy 1,4-diketones in high regioselectivity, diastereoselectivity and good enantioselectivity. This reaction provides an easy access to optically active tertiary alcohols, which are flanked by two carbonyl groups for further elaborations.     

Copper-catalyzed diversified annulations between α-diketones and alkynyl α-diketones

Copper-catalyzed divergent annulations between α-diketones and alkynyl α-diketones have been achieved, delivering a series of highly functionalized and biologically important cis-hexahydro-2Hcyclopenta[b]furan(HCPF) and 2-hydroxydihydrofuran-3(2H)-one(HDFO) products with high levels of stereoselectivity under identical conditions. The protocol features the use of earth-abundant copper catalyst, mild conditions, shortening synthetic routes in constructing different molecular frameworks, and reduc...     

Asymmetric allylation of unsymmetrical 1,3-diketones using a BINAP-palladium catalyst

[reaction: see text] The chiral palladium complex generated in situ from [Pd(eta(3)-allyl)Cl](2) and (R)-BINAP is a good catalyst for the catalytic asymmetric allylation of 1,3-diketones. The reaction provided chiral 2,2-dialkyl-1,3-diketones with 64-89% ee in high yields (13 examples). Enantiomeric excesses are strongly affected by the gamma-substituent of the allylic substrates. A variety of unsymmetrical 1,3-diketones were alkylated with cinnamyl acetate in good enantioselectivities via use of the BINAP-palladium catalyst (77-89% ee).     

Synthesis of fluorinated α-diketones and as-triazines and quinoxalines

Benzylheptafluoropropyl ketone and 1,8-diphenyl-3,3,4,4,5,5,6,6-octafluoro-2,7-octafluoro-2,7-octanedione were prepared by the reaction of benzylmagnesium chloride with heptafluorobutyric acid and octafluoroadipic acid, respectively. Oxidation of the methylene ketones with selenium dioxide produced 1-phenyl-3,3,4,4,5,5,5-heptafluoro-1,2-pentanedione and 1,8-diphenyl-3,3,4,4,5,5,6,6-octafluoro-1,2,7,8-octanetetrone. Both α-diketones were yellow and readily formed crystalline hydrates. Several alternate routes to the synthesis of the fluorinated α-diketones were investigated. The α-diketones were reacted with amidrazones and aromatic $\text{o}$-diamines to form $\text{as}$-triazines and quinoxalines, respectively.     

Enantioselective monoreduction of 2-alkyl-1,3-diketones mediated by chiral ruthenium catalysts. dynamic kinetic resolution

The reduction of 2-alkyl-1,3-diketones using (R,R)- or (S,S)-RuCl[N-(tosyl)-1,2-diphenylethylenediamine](p-cymene) in the presence of formic acid and triethylamine affords syn-2-alkyl-3-hydroxy ketones as the major products with high enantioselectivity. [reaction: see text]     

Adamantyl-containing fluorinated 1,3-diketones

A convenient one-step procedure has been developed for the synthesis of fluorine-containing 2-(adamant-l-yl)-1,3-diketones by reaction of fluorinated 1,3-diketones with 1,3-dehydroadamantane. The products can be used as starting compounds for the preparation of new fluorinated adamantyl-containing heterocyclic compounds.     

Water as an additive for selective synthesis of saturated 1,4-diketones and tetrasubstituted furans directly from 1,4-enediones

Water-controlled and phosphine-mediated selective synthesis of saturated 1,4-diketones and tetrasubstituted furans has been developed directly from 1,4-enediones. Saturated 1,4-diketones were selectively obtained in acetone with water as an additive, whereas tetrasubstituted furans were selectively obtained in anhydrous 1,2-dichloroethane. A large variety of functional groups are tolerated under these reaction conditions, including electron-rich, electron-poor, halogen, and heteroaryl substituents. This method also has significant advantages in easily available substrates, mild reaction conditions, and high reaction efficiency.     

Efficient synthesis of imidazoles from aldehydes and 1,2-diketones using microwave irradiation

[reaction: see text] A simple, high-yielding synthesis of 2,4,5-trisubstituted imidazoles from 1,2-diketones and aldehydes in the presence of NH(4)OAc is described. Under microwave irradiation, alkyl-, aryl-, and heteroaryl-substituted imidazoles are formed in yields ranging from 80 to 99%. Short syntheses of lepidiline B and trifenagrel illustrate the utility of this approach.     

Unexpected synthesis of 1,3,5-triarly-1,5-diketones from aryl ketones via di-enamine mechanism

An unexpected reaction of aryl ketone with acetohydrazone of aromatic aldehyde via 1,2-di-enamine/di-iminium mechanism was discovered, leading to efficient synthesis of 1,3,5-triaryl-1,5-diketones in good to excellent yields.     

Palladium-catalyzed carbonation-diketonization of terminal aromatic alkenes via carbon-nitrogen bond cleavage for the synthesis of 1,2-diketones

A palladium-catalyzed carbonation-diketonization reaction of terminal alkenes via carbon-nitrogen bond cleavage under an atmosphere of oxygen has been developed. A series of 1,2-diketones were readily prepared from the reaction of aromatic terminal alkenes with nitroalkanes.     

B2pin2-mediated copper-catalyzed oxidation of alkynes into 1,2-diketones using molecular oxygen

An intriguing aerobic oxidation of alkynes through copper catalysis is described, in which bis(pinacolato)diboron (B₂pin₂) played a dominant intermediary role in the formation 1,2-diketones. This novel protocol, which can be performed at room temperature, is versatile for various substituted alkynes, including diarylalkynes and arylalkylalkynes. The mechanism of this reaction was preliminarily investigated by control experiments.     

Condensation of fluorosubstituted benzaldehydes with amines and cyclic 1,3-diketones

Condensation of fluorosubstituted benzaldehydes with 2-naphthyl or 6-quinolylamine and cyclic β-diketones (,3-cyclohexanedione, dimedone, and 1,3-indandione) provided new fluoroderivatives of benzo[a]-acridine, 4,7-phenanthroline, and benzo[f]indeno[1,2-b]quinoline. Forming in the course of the reaction fluorophenylmethylene-2-naphthyl-(or 6-quinolyl)amines, arylbis(cyclohexane-1,3-dion-2-yl)methanes, and 2-(fluorophenylmethylene)-1,3-indandiones were isolated.     

Samarium diiodide promoted formation of 1,2-diketones and 1-acylamido-2-substituted benzimidazoles from N-acylbenzotriazoles

N-Acylbenzotriazoles, when treated with samarium diiodide in THF, undergo self-coupling reaction to afford 1,2-diketones in good to excellent yields; while when treated with samarium diiodide in CH₃CN, they undergo ring-opening reaction to afford 1-acylamido-2-alkyl (or aryl) benzimidazoles in reasonable to good yields. A plausible mechanism was suggested.     

Rhodium-catalyzed addition of aryl boronic acids to 1,2-diketones and 1,2-ketoesters

The metal complex Rh(acac)(CO)₂ in the presence of dicyclohexylphenylphosphine provides a useful catalyst system for the addition of boronic acids to 1,2-diketones and 1,2-ketoesters. The best yields were obtained when the transformation was performed in DME/H₂O at 80 °C with 4 equiv of the boronic acid. The results discussed herein extend the scope of the addition of arylboronic acids to highly activated diketones and ketoesters. The products of the reaction are useful in the synthesis of natural products containing oxygenation next to esters or ketones.     

Reaction of 1-amino-, 2-amino-, and 1,2-diaminoimidazoles with β-diketones

1,2-Diamino-4-phenylimidazolium perchlorate condenses with 2 mole of β-diketones to give pyrimido[2′,1′:2,3]imidazo[1,5-b]pyridazinium derivatives, while, like 1-amino-2-mercapto-4-phenylimidazole, to give imidazo[1,5-b]pyridazine derivatives. Salts of 1-benzylideneamino- and 1-(2-thiazolyl)-2-aminoimidazoles react with β-diketones to give substituted imidazo[1,2-a]pyrimidinium derivatives.