Synthesis,characterization, and crystal structures of α, α′-bis(substituted-benzylidene)cycloalkanone derivatives by nano-TiO<Subscript>2</Subscript>/HOAc

A new and economical synthesis of α, α′-bis(substituted-benzylidene)cycloalkanones has been achieved by the reaction of cycloalkanones with different aromatic aldehydes using nano-TiO₂/acetic acid as a catalyst in ethanol under reflux conditions with excellent yields. Five new products and three new single crystal structures are reported.     

Copper Triflate–Catalyzed Cross‐Aldol Condensation: A Facile Synthesis of α,α′‐Bis(Substituted Benzylidene) Cycloalkanones

A facile, efficient, and clean procedure is described for synthesis of α,α′‐bis(substituted benzylidene) cycloalkanones with good yields by the reaction of cycloalkanones with aromatic aldehydes using Cu(OTf)₂ as catalyst. The catalyst was easily recovered and reused without loss of activity.     

Electron transfer reactions between vinylmagnesium bromide and phenyl-substituted methyl chlorides

The reaction of vinylmagnesium bromide ( 1 ) with trityl chloride ( 2 ) was investigated and the products were identified as triphenylmethane ( 3 ) (81 %), acetylene ( 4 ) (74%), trityl peroxide ( 6 ) (4%), and minute amounts of triphenylpropene ( 7 ) and p-diphenylmethyltetraphenylmethane ( 8 ). The results indicate that 1 possesses reducing property. The reaction mixture showed an ESR spectrum identical with that for trityl radical and the CIDNP of enhanced absorption for 4-H of l-diphenylmethylene-4-trityl-2,5-cyclohexadiene ( 9 ). Trapping experiment with styrene decreased the amount of 3 but had no effect on the formation of 4. The reducing property of 1 is discussed and one electron transfer mechanism for the reaction of 1 with 2 is proposed. S-T₀ mixing between trityl and·MgBr occurred and the coupling of polarized trityl radical with another trityl radical resulted in the formation of polarized dimeric product. The different character between the reaction of 1 and 2 and that of 1 and diphenylmethyl chloride ( 10 ) may be rationalized by the different electron-accepting abilities between 2 and 10. The origin of CIDNP effect shown by the product tetraphenylethane ( 11 ) for the reaction of 1 with 10 is also explained according to Kaptein's sign rule.     

Cross-aldol Condensation of Cycloalkanones and Aromatic Aldehydes in the Presence of Nanoporous Silica-based Sulfonic Acid (SiO2-Pr-SO3H) under Solvent Free Conditions

The aromatic aldehydes underwent cross aldol condensation with cycloalkanones in the presence of a catalytic amount of nanoporous silica-based sulfonic acid (SiO2-Pr-SO3H) under solvent-free conditions to afford the corresponding α,α’-bis(substituted benzylidene)cycloalkanones in excellent yields with short reaction time without any side reactions. This method is very general, simple and environmentally friendly in contrast with other existing methods. SiO2-Pr-SO3H was proved to be an efficient heterogeneous solid acid catalyst, which could be easily handled and removed from the reaction mixture by simple filtration, and also recovered and reused without loss of reactivity.     

ZrCl4 as an Efficient Catalyst for Crossed‐Aldol Condensation of Cyclic Ketones with Aromatic Aldehydes in Refluxing Ethanol

The aldol condensation reaction of cyclic ketones with aromatic aldehydes in ethanol under reflux conditions using ZrCl₄ as a catalyst to afford the corresponding α,α′‐bis(substituted benzylidene and cinnamylidene)cycloalkanones in excellent yields has been described. No self‐condensation product was produced.     

Application of Ball Milling Technology to Carbohydrate Reactions: I. Regioselective Primary Hydroxyl Protection of Hexosides and Nucleoside by Planetary Ball Milling‡

Dry ball milling of hexosides with trityl chloride in the presence of DABCO or Na₂CO₃ has been found to result in their complete conversion to the respective 6‐O‐trityl ethers. Further wet grinding of the reaction mixture with Ac₂O in the presence of DMAP led to the respective fully protected hexosides in good to excellent yields after isolation. It has been found to be an effective one‐pot two‐step synthesis under solvent‐free condition. The speed of homogenization has been shown to highly influence the rate and outcome of the reaction, and commercially available planetary ball mill has been proved to be very convenient for carrying out the reaction under standardized and reproducible conditions.     

A facile synthesis of 1-cycloalkenyl isothiocyanates with silicon tetraisothiocyanate

The reaction of cycloalkanones with silicon tetraisothiocyanate in the presence of (Me₃SiO)₂SO₂^?nBu₃SnF or Zn(NCS)₂ provides 1-cycloalkenyl isothiocyanates in good yields under mild conditions.     

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system,as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph₃CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph₃CMe) and the triphenylcarbonium ion (“trityl ion”, Ph₃C⁺). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al₂Cl₃Me₄⁻. Large excess of trityl chloride causes the formation of AlCl₄⁻, and probably AlCl₃Me⁻ and AlCl₂Me₂⁻ anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.     

A novel route to linear polycyclic compounds. Diastereoselective aldol-type reactions of α-sulfonyl carbanions

Aromatic derivatives, bifunctionalized at vicinal benzylic positions with Br and SO₂PH groups undergo one-pot annulations with unactivated cycloalkanones. The ring closure occurs by a diastereoselective aldol-type reaction of α-sulfonyl carbanions.     

On the interaction of triphenylmethyl salts with α-methylstyrene

The interaction of triphenylmethyl salts with α-methylstyrene and 1,1-diphenylethylene was investigated. With 1,1-diphenylethylene at a monomer-initiator ratio of 2 (room temperature), mainly 1,1,3-triphenyl-3-methyl-indane was isolated, whereas at a ratio of 100 (?10°C), the dimer 1,1,3,3-tetraphenylbutene-1 mainly formed. In both cases no addition of the trityl group was registered. In the interaction of α-methylstyrene with Ph₃C⁺SbCl at a monomer-initiator ratio of 2(room temperature) a pure 1,3,3-trimethyl-1-phenylindane was isolated and no addition of the trityl group to the double bond was recorded. The initiation reaction of α-methylstyrene polymerization by trityl and chlorinated trityl salts was studied at temperatures from ?20 to 0°C and different concentrations. The oligomers obtained with (pCI-C₆H₄)₃C⁺ were investigated by elemental analysis and fluorescence spectroscopy. The presence of Ph₃CH in the reaction mixture was demonstrated by GLC and NMR spectra. The results obtained give evidence that the initiation of α-methylstyrene polymerization involves hydride abstraction from the monomer.     

Unusual Tritylation Reactions of Tricyclic Analogues of Acyclovir and an Attempt to Elucidate Their Mechanism

In reference to our earlier observation that the 3,9‐dihydro‐3‐[(2‐hydroxyethoxy)methyl]‐6‐methyl‐9‐oxo‐5H‐imidazo[1,2‐a]purine (6‐Me‐TACV) tricyclic antiviral agent derived from acyclovir undergoes unusual C‐tritylation to 7‐trityl and 7‐[4‐(benzhydryl)phenyl] derivatives enforced by a 6‐Me substituent, we studied tritylation of 6‐Ph ( 1a ) and 6‐(4‐MeOPh) ( 1b ) TACV derivatives. The treatment of 1a and 1b with TrCl in K₂CO₃/DMF resulted exclusively in the formation of 7‐[4‐(benzhydryl)phenyl] derivatives 2a , 2b , 3a , 3b , and 4a . Inhibition experiments with radical scavengers DNB and DBNO indicated a single‐electron‐transfer (SET) mechanism for this reaction. Analogous experiments with unsubstituted TACV and 6‐Me‐TACV suggest that the nature of the substituent at C(6) determines the reaction mechanism. The presence of a 6‐aryl substituent results in the exclusive formation of 4‐(benzhydryl)phenyl derivatives via a SET mechanism. On the contrary, when C(6) is unsubstituted, trityl derivatives are the only products of the S_n reaction. In the case of 6‐Me‐TACV, concomitant SET and S_n mechanisms direct the reaction towards 4‐(benzhydryl)phenyl and trityl products.     

Oxidation of cycloalkanones with hydrogen peroxide: an alternative route to the Baeyer-Villiger reaction. Synthesis of dicarboxylic acid esters

The acid-catalyzed oxidation of cycloalkanones C₅-C₈ and C₁₂ with hydrogen peroxide in alcohols was performed, and dicarboxylic acid esters were obtained as the major products in 53-70% yields. In the first step, geminal bishydroperoxides are generated from five-to-seven-membered cyclic ketones. The Baeyer-Villiger reaction is a side process accompanied by the formation of ω-hydroxycarboxylic acid esters.     

Carbocation catalysis in confined space: activation of trityl chloride inside the hexameric resorcinarene capsule

Carbocation catalysis can be performed inside the confined space of the hexameric resorcinarene capsule. The inner cavity of the capsule can host the trityl carbocation, which catalyses the Diels–Alder reaction between dienes and unsaturated aldehydes. Experimental results and in silico calculations show that the hexameric resorcinarene capsule C₆ can promote the formation of the trityl carbocation from trityl chloride through the cleavage of the carbon–halogen bond promoted by OH⋯X⁻ hydrogen bonding. Here it is shown that the combination of the nanoconfined space and the latent carbocation catalysis provides a convenient complementary strategy for the typical carbocation catalysis. The latent strategy bypasses the typical pitfalls associated with active carbocations and provides control of the reaction efficiency in terms of reaction rate, conversion, and selectivity.

The hexameric resorcinarene capsule is able to promote carbocation catalysis inside its cavity.     

Catalytic annulation of 1-substituted-3-en-1-yn-5-als with cycloalkanones using acid-base dual catalysts

CpRu(PPh₃)₂Cl and DBU dual catalysts in combination enable a one-pot annulation of 1-R-3-en-1-yn-5-als (R = aryl, alkenyl, alkyl) and cycloalkanones to give highly substituted benzene products. This catalytic reaction consists of a tandem aldol condensation, dehydration and aromatization through a 1,7-hydrogen shift; the resulting 1-indanones and α-tetralones are obtained in moderate to good yields.     

Cationic polymerization of isobutyl vinyl ether initiated with transition‐metal ate complexes

The cationic polymerization of isobutyl vinyl ether was examined with transition‐metal ate complexes with trityl cation as initiators. The initiators were generated by the reaction of triphenylmethyl chloride [trityl chloride (TrCl)] with ate complexes of Nb, Mo, and W with lithium cation, which were obtained in situ by the reaction of the transition‐metal halides with anionic reagents (organolithium or lithium amide). When the polymerization was initiated with a mixture of TrCl and Li⁺[NbH₅(NnBuPh)]^?, the resulting poly(isobutyl vinyl ether)s had narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight = 1.13–1.20). Although the polymerization was supposed to be initiated by the electrophilic attack of the trityl cation, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the resulting poly(isobutyl vinyl ether)s revealed the presence of H at the α‐chain end. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2636–2641, 2006     

Mass spectrometry of five classes of trityl compounds-loss of 12C from (C6H5)313CH

The mass spectra of 25 triphenylmethyl (trityl) substituted compounds have been recorded. The trityl cation m/e 243 appears as a peak of major intensity for all classes of compounds examined; these contained trityl-carbon, trityl-nitrogen, trityl-oxygen or trityl-sulfur bonds. Fragmentation of the non-trityl portion of the molecules produced simple ions whose origin was predictable or of low intensity. A mechanism for the decay of the trityl cation is presented which is based upon retention of the α-carbon. Supporting evidence was afforded by mass spectral analysis of (C₆H₅)₃¹³CH in which all fragments from the trityl cation appear to retain nearly all of the ¹³C.     

Solvent-Free,Cross-Aldol Condensation Reaction Using Silica-Supported,Phosphorus-Containing Reagents Leading to α,α′-Bis(arylidene)cycloalkanones

This article describes an efficient, simple, and clean method for the synthesis of α,α′-bis(arylidene, furylidene and cinnamylidene)cycloalkanones under solvent-free conditions. The cross-aldol condensation of cycloalkanones with aldehydes in the presence of silica-supported phosphorus pentoxide (P₂O₅/SiO₂) or silicaphosphinoxide (silphox, [POCl_3-n(SiO₂)_n]) as heterogeneous reagents produces the title compounds in good to excellent yields.     

Deprotection of α-imidazole/benzimidazole ribonucleosides by catalytic carbon tetrabromide initiated photolysis

Several protected benzimidazole and imidazole α-ribonucleosides were deprotected in excellent yield at ambient temperature using CBr₄ initiated photolysis in methanol at ambient temperature. No selectivity was observed and both trityl and isopropylidene groups were deprotected under the reaction conditions.     

A new (S)-prolinamide modified by an ionic liquid moiety—a high performance recoverable catalyst for asymmetric aldol reactions in aqueous media

New prolinamide derivatives modified with ionic liquid moieties were synthesized and studied as organocatalysts in asymmetric aldol reactions in water. Aldol reactions between cycloalkanones or methylketones and aromatic aldehydes proceeded under studied conditions with high conversions (yields), diastereo- and enantioselectivities in the presence of a hydrophobic catalyst bearing a PF₆ anion (1-5 mol %). The procedure is scalable and the catalyst retained its diastereo- and enantioselectivity over at least four reaction cycles and its activity over at least three reaction cycles.     

Cationic polymerization of N-vinyl carbazole by trityl salts—II.: New considerations about the mechanism

The mechanism of initiation in the polymerization of N-vinyl carbazole by trityl salts in methylene dichloride has been investigated by spectroscopic studies of final reaction mixtures and molecular weight analysis. The proposed reaction mechanism involves regeneration of the Ph₃C⁺ cation and propagation through a dication as active species.