Electroreductive acylation of aromatic ketones with acylimidazoles

[Reaction: see text]. The intermolecular reductive coupling of aromatic ketones with acylimidazoles was effected by electroreduction in the presence of chlorotrimethylsilane and gave alpha-trimethylsiloxy ketones and esters. The best result was obtained using Bu4NPF6 as a supporting electrolyte and a Pb cathode in THF. The alpha-trimethylsiloxy-containing products were transformed to the corresponding alpha-hydroxy ketones and esters by treatment with TBAF in THF. This method was also effective for the intramolecular reductive coupling of delta- and epsilon-keto acylimidazoles.     

Samarium(II)-mediated reactions of gamma,delta-unsaturated ketones. Cyclization and fragmentation processes

[reaction: see text] On treatment with samarium(II) iodide, gamma,delta-unsaturated ketones undergo very different processes depending upon the nature of the reaction conditions. Employing samarium(II) iodide and MeOH, functionalized syn-cyclopentanol products are obtained stereoselectively. Mechanistic studies suggest that this cyclization occurs via a sequential reduction/intramolecular aldol reaction. With samarium(II) iodide and HMPA, products of a 4-exo-trig cyclization and of an interesting fragmentation reaction are observed.     

Alkyl, unsaturated, (hetero)aryl, and N-protected alpha-amino ketones by acylation of organometallic reagents

Stable and easily accessible N-acylbenzotriazoles, derived from a variety of aliphatic, unsaturated, (hetero)aromatic, and N-protected alpha-amino carboxylic acids, were reacted with Grignard and heteroaryllithium reagents to afford corresponding ketones in good to excellent yields.     

Stereocontrol in the EtAlCl(2)-induced cyclization of chiral gamma,delta-unsaturated methyl ketones to form cyclopentanones

EtAlCl(2)-induced cyclization of chiral gamma,delta-unsaturated ketones 11c and 17b takes place mainly from the expected face. The selectivity is modest for 11c (60:40) in which the large substituent is a primary alkyl group and the medium substituent is a methyl group and excellent for 17b (93:7) in which the large substituent is a cyclohexyl group and the medium substituent is a methyl group. The cyclization of 17a is anomalous, suggesting that the phenyl group has more than a simple steric effect.     

Fluoro-ketones. III. Synthesis of aryl perfluoroalkylether ketones by the Friedel-Crafts acylation

The first successful application of aliphatic perfluoroacid halides containing an ether function, in the Friedel-Crafts acylation is reported.     

Preparation of beta-keto esters and beta-diketones by C-acylation/deacetylation of acetoacetic esters and acetonyl ketones with 1-acylbenzotriazoles

Acyl-, aroyl-, and heteroaroyl-acetic esters 6a-f and 8a-l are prepared by reactions of 1-acylbenzotriazoles 1a-k with acetoacetic esters 5 or 7a,b in the presence of sodium hydride followed by regioselective deacetylation. Similar C-acylation/deacetylation of acetylacetone and benzoylacetone affords beta-diketones 10a-d and 13a-c, respectively.     

Rearrangement of allyl homoallyl ethers to gamma,delta-unsaturated carbonyl compounds catalyzed by iridium complexes

Iridium complexes were found to promote the conversion of allyl homoallyl ethers to gamma,delta-unsaturated carbonyl compounds. For example, treatment of 1-allyl-1-allyloxycyclohexane in the presence of catalytic amounts of [Ir(cod)Cl](2), PCy(3), and Cs(2)CO(3) in toluene at 100 degrees C afforded 4-cyclohexyliden-2, 3-dimethylbutanal in 74% yield. The reaction presumably proceeds through double bond migration to allyl vinyl ethers, which then undergo the Claisen rearrangement.     

Synthesis of delta-tributylstannyl-alpha,beta,gamma,delta-unsaturated aldehydes from pyridines

Zincke aldehydes, which are readily available from the ring-opening reaction of pyridinium salts, are easily converted into delta-tributylstannyl-alpha,beta,gamma,delta-unsaturated aldehydes (stannyldienals) by the action of tributylstannyllithium. This reaction appears to proceed via 1,6-stannyllithium addition/elimination of lithium dialkylamide. Several stannyldienals of significant utility for the synthesis of polyene natural products have been made by this route, which proceeds in modest yields, but is successful on multigram scale using inexpensive reagents. Simple stannylenals and stannylenones are similarly available from the corresponding vinylogous amides.     

Rhodium-catalyzed acylation with quinolinyl ketones: carbon-carbon single bond activation as the turnover-limiting step of catalysis

The rhodium-catalyzed intramolecular carboacylation of quinolinyl ketones serves as an ideal subject for the mechanistic study of carbon-carbon bond activation. Combined kinetic and NMR studies of this reaction allowed the identification of the catalytic resting state and determination of the rate law, (12)C/(13)C kinetic isotope effects, and activation parameters. These results have identified the activation of a ketone-arene carbon-carbon single bond as the turnover-limiting step of catalysis and provided quantitative detail into this process.     

Total synthesis of antofine using the net [5+5]-cycloaddition of gamma,delta-unsaturated carbene complexes and 2-alkynylphenyl ketones as a key step

A compound containing all of the carbons of the anticancer agent antofine was produced in a single step from the coupling of a gamma,delta-unsaturated carbene complex with a 2-alkynylphenyl ketone derivative. Subsequent conversion to antofine was effected in three steps.     

Asymmetric Eschenmoser-Claisen rearrangement for anti-beta-substituted gamma,delta-unsaturated amino acids

Optically active anti-beta-substituted gamma,delta-unsaturated amino acids are important synthetic building blocks in organic synthesis and for peptidomimetics. A novel asymmetric Eschenmoser-Claisen rearrangement with use of a C2-symmetric chiral auxiliary was developed to generate this type of amino acid. Excellent diastereoselectivities and high enantioselectivities (87-93% ee) were obtained after the chiral auxiliary was removed via iodolactonization/zinc reduction.     

Synthesis of Anti-beta-substituted gamma,delta-unsaturated amino acids via Eschenmoser-Claisen rearrangement

Anti-beta-substituted gamma,delta-unsaturated amino acids have been synthesized via a novel design of the Eschenmoser-Claisen rearrangement. The rearrangement gives good isolated yields and excellent diastereoselectivity due to (Z)-N,O-ketene acetal formation and the pseudochairlike conformations of the reaction intermediates. Upon reductive hydrolysis, important novel amino acids and amino alcohols were synthesized for the first time via this methodology.     

The reaction of trialkylstannylmethyllithium with α,β-epoxy ketones. A preparative method of β, γ-unsaturated ketones by homologation of α, gb-unsaturated ketones

α, β-epoxy ketones $\text{2}$, upon treatment with two equivalents of trialkylstannylmethyllithium $\text{1}$, afforded cyclopropanols $\text{3}$ as a single product in acyclic system, and a mixture of cyclopropanols $\text{3}$ and methylene 1,2-diols $\text{4}$ in cyclic system. Under acidic conditions, the cyclopropanols gave β, γ-unsaturated ketones $\text{5}$ in good yields.     

Palladium catalysed cyclisation-carbonylation of enynes to give cyclic gamma,delta-unsaturated acids

In the presence of acetic acid, trifurylphosphine and CO (2 atm), palladium catalyses the conversion of a range of enynes to cyclic delta,gamma-unsaturated carboxylic acids in good yield.     

Synthesis of vinyl-substituted beta-diketones for polymerizable metal complexes

[reaction: see text] Polymerizable beta-diketones for application to metal ion coordination have been prepared and characterized. Bromine-substituted beta-diketones were synthesized under Claisen-Schmidt-type condensation conditions. Vinyl groups were substituted for the halide by one of two types of Heck coupling with high-pressure ethylene. The type of Heck coupling employed was dictated by the thermal sensitivity of the substrate. Seven vinyl-substituted beta-diketones were synthesized, including several new ones, by this method. The beta-diketones were characterized by GC-MS, FT-NMR, FT-IR, and microanalysis.     

Regioselective acylation of ginsenosides by Novozyme 435

Ginsenosides from Panax species were acylated regioselectively by Novozyme 435 with vinyl acetate as the acetyl donor in organic solvents to afford mono-acyl ginsenosides.