Mechanism of oxidation of α,β-unsaturated thiones by singlet oxygen

Photo-oxidation of α,β-unsaturated thiones yields the corresponding ketones as the only product. Studies carried out on three systems, namely thioketones, α,β-unsaturated thiones and thioketenes, have revealed that there exists a similarity in their mechanism of oxidation. It has been suggested that the thiocarbonyl chromophore is the site of attack by singlet oxygen in α,β-unsaturated thiones and that the adjacent C-C double bond is inert under these conditions. Absence of sulphine during the oxidation of α,β-unsaturated thiones is attributed to the electronic factors operating on the zwitterionic/diradical intermediate. While α,β-unsaturated ketones are poorly reactive, α,β-unsaturated thiones are highly reactive toward singlet oxygen.     

HBTU Mediated Synthesis of α,β-Unsaturated γ-Lactams from E-α,β-Unsaturated γ-Amino Acids

The α,β-unsaturated γ-lactams have been found in many biologically active peptide natural products. Due to their biological activities, extensive efforts have been made in the literature to synthesize the α,β-unsaturated γ-lactams. Here, we are reporting the spontaneous transformation of E-α,β-unsaturated γ-amino acids into α,β-unsaturated γ-lactam through in-situ activation of free carboxylic acid using peptide coupling reagent HBTU and base DIPEA at room temperature. The transformation also involves the E→Z isomerization of α,β-unsaturated γ-amino acids. The reaction is also compatible with the peptides consisting of E-α,β-unsaturated amino acids at the C-terminus. The α,β-unsaturated γ-lactams were isolated in very good yields. Even though the reaction required very mild conditions, the products were isolated in the form of a racemic mixture. However, the products can be separated under a chiral environment. No α,β-unsaturated γ-lactams were observed if the reaction was performed in the presence of free amines. In addition, no racemization was observed during the peptide synthesis. The analysis of the reactions of various substrates revealed that amide NH and γ-CH are important for lactamization. No α,β-unsaturated γ-lactams or E→Z isomerization products were observed in the case of N-Me-(E)-α,β-unsaturated γ-amino acids, whereas in the case of E-α,β-unsaturated γ,γ-dimethyl amino acid α,β-unsaturated γ-lactam was isolated, however, with low yield.     

Reactions of β-heteroatom substituted α,β-unsaturated ketones with dimethylsulfonium methylide

β-Alkoxy- and β-alkylthio α,β-unsaturated ketones react with dimethylsulfonium methylide (DMSM) to give a furan, while β-anilino α,β-unsaturated ketones give the pyrrole. β,β-Bis(alkylthio) α,β-unsaturated ketones react with DMSM to afford the methylene inserted products, λ,λ-bis(alkylthio) β,λ-unsaturated ketones.     

Synthesis of 2-naphthols via carbonylative Stille coupling reaction of 2-bromobenzyl bromides with tributylallylstannane followed by the Heck reaction

A method for the synthesis of 2-naphthols 4 is described. The carbonylative Stille coupling reactions of 2-bromobenzyl bromides with tributylallylstannane to produce 2-bromobenzyl β,γ-unsaturated ketones 2 in satisfactory to excellent yields has been achieved. The isomerization of 2-bromobenzyl β,γ-unsaturated ketones 2 can readily occur under basic conditions to generate 2-bromobenzyl α,β-unsaturated ketones 3. The 2-bromobenzyl α,β-unsaturated ketones 3 can be transformed into 2-naphthols 4 via intramolecular Heck reaction in satisfactory to good yields.     

Palladium-catalyzed regioselective reactions of α-acetoxy-β,γ-unsaturated nitriles and γ-acetoxy-α,β-unsaturated ester with nucleophiles

α-Acetoxy-β,γ-unsaturated nitriles react at room temperature with malonates and acetoacetates in the presence of palladium-phosphine complexes as a catalyst to give γ-substituted α,β-unsaturated nitriles selectively. Also γ-acetoxy-α,β-unsaturated ester was attacked at y-position by malonate.     

Synthese d'aziridines N-non substituees par reduction de sels d'hydrazonium

Z and E N,N,N-trimethylhydrazonium iodides from α,β-unsaturated cyclohexenones are reduced in good yields into saturated aziridines or α,β-unsaturated aziridines by sodium bis (2-methoxy ethoxy) aluminium hydride. Partly hydrolysed hydride leads to reverse proportions of saturated and α,β-unsaturated aziridines.     

Copper-catalyzed β-boration of α,β-unsaturated carbonyl compounds with tetrahydroxydiborane

The copper-catalyzed β-boration of α,β-unsaturated carbonyl compounds with tetrahydroxydiborane has been developed. This diboron reagent allows direct, efficient access to boronic acids and their derivatives. Primary, secondary, and tertiary α,β-unsaturated amides are converted to the corresponding β-trifluoroboratoamides in good to excellent yields. The β-boration of a variety of α,β-unsaturated esters and ketones is also reported.     

A novel and efficient procedure for the preparation of allylic alcohols from α,β-unsaturated carboxylic esters using LiAlH4/BnCl

A new and efficient method for the reduction of α,β-unsaturated carboxylic esters to allylic alcohols utilizing LiAlH₄/BnCl is described. Various α,β-unsaturated esters, including the coumarins bearing α,β-unsaturated lactone skeleton, can be converted smoothly into their corresponding allylic alcohols in high yields under mild conditions with short reaction times.     

A modular approach to α,β-unsaturated N-aryl ketonitrones

A modular approach to α,β-unsaturated N-aryl ketonitrones has been developed. Specifically, condensation of anilines and enals followed by alkylation of the resulting α,β-unsaturated imines provided N-allyl anilines, which were subjected to oxidation with Oxone® to form α,β-unsaturated N-aryl ketonitrones. This modular approach is general and provides rapid access to diversely substituted α,β-unsaturated N-aryl ketonitrones with a single purification step in good yields.     

Homolgation of β-silyl-α,β-unsaturated esters

Treatment of β-trimethylsilyl-α,β-unsaturated esters with diazomethane results in a stereospecific homolgation to the corresponding γ-trimethylsilyl-α,β-unsaturated esters.     

Copper-mediated synthesis of α-trifluoromethylthio- and seleno-α,β-unsaturated carbonyl compounds

A novel route to the synthesis of α-trifluoromethylthio- and seleno-α,β-unsaturated carbonyl compounds via a copper-mediated trifluoromethylthiolation/trifluoromethylselenolation of α-halo-α,β-unsaturated carbonyl substrates is reported.     

Synthesis of 3-substituted indole by AlCl3-promoted reaction of β,γ-unsaturated ketone with indole

A one-pot Lewis acid-promoted reaction condition of β,γ-unsaturated ketone with indole was developed for the synthesis of 3-substituted indoles with moderate to good yields. A Lewis acid such as AlCl₃ was shown to be a promising promoter for in situ isomerization of β,γ-unsaturated ketone to its corresponding α,β-unsaturated ketone, then undergoing Friedel–Crafts Michael addition reaction with indole to afford 3-substituted indole.     

Addition of Organosamarium Reagents toα, β-Unsaturated Esters

Compared to the extensive use of samarium diiodide in organic synthesis', little reportsappeared on the application of samarium metal in organic synthesis. As early as 1971Evans and co-workers had prepared phenylsamarium iodide from iodo-benzene andsamarium metal'. But they found that samarium is not so active as ytterbium. In 1986Fukuzawa also prepared the organosamarium intermediate similar to Grignard reagent'.It was Curran who firstly proved and named the samarium Grignard reaction in 19…     

α-Bromo-β,γ-unsaturated ketenes for the synthesis of α-benzylamino-β,γ-unsaturated acids

The synthesis of α-benzylamino-β,γ-unsaturated acids has been developed starting from α-bromo-α,β-unsaturated chlorides. Via treatment of the acyl chlorides with (R)-pantolactone in the presence of TEA, the in situ formation of the deconjugated ketenes and their direct transformation into chiral esters was performed. The substitution of bromine with benzylamine, followed by acid hydrolysis, allowed to us obtain enantiomerically enriched α-benzylamino-β,γ-unsaturated acids.     

Mn(III) acetate-mediated regioselective benzylation of various α,β-unsaturated and β-alkoxy-α,β-unsaturated ketones

We describe herein the results of manganese(III) acetate mediated α′-benzylation of various α,β-unsaturated and β-alkoxy-α,β-unsaturated ketones in moderate yields.     

An Aldol Reaction of Boron Enolates Generated by the 1,4-Addition of B-Br-9-BBN to α, β-Unsaturated Ketones. A Synthesis of α-Bromomethyl-α, β-Unsaturated Ketones

α-Bromomethyl-α,β-unsaturated ketones can be prepared easily by the successive addition of α,β-unsaturated ketones and then aldehydes to B-bromo-9-borabicyclo[3.3.1]nonane.     

The reactivity of furanoid and pyranoid glycals towards aromatic Grignard reagents and a nickel catalyst

By reaction with aromatic Grignard reagents in the presence of low valent nickel species at low temperature, the 1,2-unsaturated furanoid glycal (1) undergoes coupling reaction to produce 2,3-unsaturated products (1a,b) as pure stereoisomers. When these reaction conditions are applied to protected 1,2-unsaturated pyranoid glycals (2, 3, 4), both cross-coupling and elimination reactions occur to give conjugated diene-alcohol derivatives (2a; 3a,b; 4a,b, respectively), in moderate yield.     

A generalised route for the synthesis of β-furyl-α,β-unsaturated aldehydes through Suzuki reactions

A general method for the synthesis of β-(2-furyl)-α,β-unsaturated aldehydes is described using the Suzuki coupling reaction of furan-2-boronic acids and β-bromo-α,β-unsaturated aldehyde derivatives.     

Lewis acid-promoted reaction of β,γ-unsaturated α,α-dimethoxy esters with silyl nucleophiles

The Lewis acid-promoted reaction of β,γ-unsaturated α,α-dimethoxy esters, which are easily prepared by the acetalization of β,γ-unsaturated α-keto esters, with silyl nucleophiles is presented. By employing trimethylsilyl enolate and allyltrimethylsilane as nucleophiles, the BF₃-promoted reactions of a series of β,γ-unsaturated α,α-dimethoxy esters bearing aromatic and aliphatic substituents proceeded at the γ-position in an SN2′ manner to furnish γ-substituted α,β-unsaturated α-methoxy esters in good yields with high regioselectivity. In contrast, the reaction using trimethylsilyl cyanide predominantly occurred at the α-position, and the reaction of silyl hydride resulted in a mixture of α- and γ-regioisomers in favor of the γ-substitution products.     

γ-Oxygenation of α,β-unsaturated esters by vinylogous O-nitroso Mukaiyama aldol reaction

A practical procedure has been developed for γ-oxygenation of α,β-unsaturated esters by a vinylogous O-nitroso Mukaiyama aldol reaction followed by a one-pot N-O bond heterolysis of the in situ generated γ-aminoxy-α,β-unsaturated esters.