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.     

Selective acylation of ribonucleotides and ribonucleosides with acylimidazoles

Selective acylation of ribonucleotides and ribonucleosides can be achieved by using N-acylimidazole on a preparative scale with good yields (50–80%). For uridine 3′-phosphate (Up): in the presence of MDCAI, the 2′-O-acyl-derivative is the main product, while in the presence of an excess of TEAH, the 5′-O-acyl-derivative is the main product. For ribonucleosides (U_R or A_R or ψ_R): in the presence of MDCAI, the acylations take place preferably at 2′-OH or 3′-OH of ribonucleosides and only 3′-O-acyl-derivatives can be isolated by crystallization; in the presence of an excess of TEAH. 5′-O-acyl-derivative is obtained as the main product. Arabinonucleoside and deoxyribonucleoside are only slowly acylated to form 5′-O-acyl-derivatives as the main products by acylimidazole in the presence of MDCAI. Possible mechanisms of these acylations have been discussed.     

Electroreductive crossed hydrocoupling of aromatic ketones with enol acetates

Cathodic reduction of aromatic ketones in the presence of enol acetates afforded crossed hydrocoupling products, that is, unsymmetrical pinacols, in which the new carbon-carbon bond formation took place between the carbonyl carbon of aromatic ketones and the carbon bearing acetoxyl group in enol acetates.     

The selective reductive acylation of a-keto imines

Reaction of α-keto imines with the $\text{in}$$\text{situ}$ generated acetylcobalt tetracarbonyl occurs only at the carbon—nitrogen double bond to give β-keto amides. An unexpected by-product was formed in several instances.     

Cobalt-catalyzed ortho-arylation of aromatic imines with aryl chlorides

An ortho-arylation reaction of aromatic imines with aryl chlorides has been achieved using a cobalt-N-heterocyclic carbene catalyst in combination with a neopentyl Grignard reagent. The reaction takes place at room temperature to afford biaryl products in moderate to good yields.     

Electroreductive crossed pinacol coupling of aromatic ketones with aliphatic ketones and aldehydes

The intermolecular crossed pinacol coupling of aromatic ketones with aliphatic aldehydes and ketones was effected by electroreduction in the presence of chlorotrimethylsilane. The best result was obtained using a Pb cathode in Bu₄NPF₆/THF. The electroreduction of aromatic 1,4-, 1,5-, and 1,6-diketones under the same conditions gave four-, five-, and six-membered 1,2-diols with trans-stereoselectivity, while the reduction of these diketones with TiCl₄-Zn produced the cis-isomers of the same intramolecular crossed pinacol coupling products predominantly.     

Cycloadditions of aromatic azomethine imines with 1,1-cyclopropane diesters

The cycloaddition of aromatic azomethine imines to 1,1-cyclopropane diesters was achieved using Ni(ClO4)2 as catalyst. The methodology gives access to unique tricyclic dihydroquinoline derivatives with dr up to 6.6:1. A nonconcerted mechanism is proposed on the basis of stereochemical analysis of the reaction.     

Synthesis of N-perfluoroalkanesulfonyl aromatic imines

N-Sulfinyl perfluoroalkanesulfonamides, R_fSO₂NSO, prepared by refluxing perfluoroalkanesulfonamideswith thionyl chloride, react easily with aromatic aldehydes giving N-perfluoroalkanesulfonyl aromatic imines, R_fSO₂N=CHAr, through elimination of sulfurdioxide.     

Electroreductive intramolecular coupling of aromatic δ- and ε-keto esters

Electroreduction of aromatic δ- and ε-keto esters in the presence of chlorotrimethylsilane and triethylamine gave five- and six-membered cyclized products. The products were transformed to the corresponding α-hydroxy ketones.     

Electrochemically promoted Friedel-Crafts acylation of aromatic compounds

Friedel-Crafts acylation is carried out with several aromatic substrates in the presence of an electrochemically active aluminium anode to minimize the inorganic reagents. Only a catalytic amount of AlCl₃ (5 mol %) is required to enable the anodic polarization of the aluminium electrode to promote continuous acylation. This process typically gave products in good yields (70-96%).     

Electroreductive intramolecular coupling of phthalimides with aromatic aldehydes: application to the synthesis of lennoxamine

The electroreductive intramolecular coupling of phthalimides with aromatic aldehydes in the presence of chlorotrimethylsilane and triethylamine led to five-, six-, and seven-membered cyclized products (58-84%). The electroreductive cyclization was applied to the total synthesis of lennoxamine.     

Regioselectivity of Friedel-Crafts acylation of aromatic compounds with several cyclic anhydrides

The Friedel-Crafts acylations of various aromatic compounds with cyclic anhydrides such as 2-(p-substituted phenyl)butanedioic, 3-phenylpentanedioic and homophathlic anhydrides were carried out under various conditions in order to obtain informations about the regioselectivity of the ring opening of the cyclic anhydrides and about the possible reaction pathways in the acylations.     

Studies of acylation kinetics of aspen wood with aromatic carboxylic acids

With the help of Erofeev-Kolmogorov and Eiring equations kinetic characteristics of acylation of the aspen wood with the aromatic carboxylic acids in presence of thionyl chloride in the trifluoroacetic acid medium were calculated and thermodynamic parameters of this process were established.     

Electrochemical activation and carboxylation of fluorine-containing aromatic imines

On the basis of a study of the processes involved in the electrochemical activation of a series of fluorine-containing aromatic imines with and without the presence of carbon dioxide it was shown that the initial stage of such processes is the formation of imine radical-anions, which can both undergo spontaneous transformations and react with CO₂ with the formation of fluorine-containing amino acids. A correlation was established between the effects of the electronic structure of the imines on the electrochemical characteristics of their reduction and on the stability of the radical-anions. A relationship was established between the parameters of electrochemical activation of the imines in the presence of CO₂ and the yields of the amino acids. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 265–271, September–October, 2008.     

Reaction of vinylidenecyclopropanes with aromatic imines in the presence of Lewis acids

1-Methyl-2-(2-methylpropenylidene)-1-phenylcyclopropane, 7-(2-methylpropenylidene)bicyclo[4.1.0]heptane, and (Z)-9-(2-methylpropenylidene)bicyclo[6.1.0]non-4-ene react with N-benzylideneanilines in the presence of boron trifluoride-ether complex to give pyrrolidine derivatives. Reactions of 1-methyl-1-phenyl-2-diphenylvinylidenecyclopropane with N-benzylideneanilines in the presence of BF₃·Et₂O, Yb(OTf)₃, or Sc(OTf)₃ lead to the formation of substituted 1,2,3,4-tetrahydroquinolines. 7-Diphenylvinylidenebicyclo[4.1.0]heptane in the presence of BF₃·Et₂O undergoes isomerization into 5-phenyl-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalene.     

Michael reactions of unsubstituted aromatic chiral imines with substituted unsaturated acid esters

The Michael reaction of chiral imines 1–3, derived from aromatic ketones’ with substituted electrophilic olefins generated asymmetric tertiary carbon centers. Nevertheless, asymmetric inductions were weaker than those usually observed with cycloalkanone imines.     

New organic activators for the enantioselective reduction of aromatic imines with trichlorosilane

N-Picolinoyl-(2S)-(diphenylhydroxymethyl)pyrrolidine was found to work as an organic activator in the reduction of aromatic imines to the corresponding amines by Cl₃SiH. The highest selectivity was 80% ee. These are the first data showing that N-formyl group is not always essential as N-protecting group of pyrrolidine derivatives for the reduction of imines by Cl₃SiH.     

Annulation of aromatic imines via directed C-H bond activation

A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh3)3RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality.     

Reaction of 6,6-dimethylfulvene with aromatic imines in the presence of Lewis acids

Formal aza-Diels-Alder (Povarov) reaction of 6,6-dimethylfulvene with aromatic imines is described for the first time.