Lewis base effects in the Baylis-Hillman reaction of imines with cyclohex-2-en-1-one and cyclopent-2-en-1-one

In the Baylis-Hillman reaction of N-benzylidene-4-methyl-benzenesulfonamide with cyclohex-2-en-1-one or cyclopent-2-en-1-one, we found that, in the presence of a catalytic amount of DMAP, the Baylis-Hillman reaction can be greatly accelerated to give the normal Baylis-Hillman adduct 1 or 3 in good or very high yields: moreover, using PBu3 as a Lewis base in the reaction of N-benzylidene-4-methylbenzenesulfonamide with cyclopent-2-en-1-one, the normal Baylis-Hillman adducts 3 could be obtained in very high yields within 5 h, however, using PBu3 or DBU as a Lewis base in the reaction of N-benzylidene-4-methyl-benzenesulfonamide with cyclohex-2-en-1-one, beside the normal Baylis-Hillman adduct 1 abnormal Baylis-Hillman adduct 3-aryl-2-[(4-methylphenyl)sulfonyl]-2-azabicyclo[2.2.2]octan-5-one 2 was formed at the same time; the substituent's effects were also examined.     

Selective Heck reaction of aryl bromides with cyclopent-2-en-1-one or cyclohex-2-en-1-one

The selective Heck reaction of cyclopent-2-en-1-one or cyclohex-2-en-1-one with aryl bromides gives a simple access to the corresponding 3-arylcycloalk-2-en-1-ones. The choice of the base was found to be crucial to avoid the formation of 3-arylcyclopentanones or 3-arylcyclohexanones as side-products. Using KF as base, DMF as solvent and Pd(OAc)₂ as catalyst, the target products were obtained in moderate to good yields with a variety of aryl bromides. Substituents such as fluoro, trifluoromethyl, acetyl, benzoyl, formyl, ester or nitrile on the aryl bromide are tolerated. Sterically congested aryl bromides or bromopyridines can also be employed.     

Pinacol rearrangement of cyclopent-3-en-1,2-diols: Cyclopentenone formation and interrupting reaction

Cyclopentenyl carbocations formed as a result of the protonation of 3,4-substituted cyclopent-3-en-1,2-diols can give either cyclopent-2-en-1-one derivatives via pinacol rearrangement or interrupted reaction products similar to the Nazarov intermediate.     

Reactions of secondary amines with derivatives of 5-(2-methyl-3-furyl)cyclopent-2-en-1-one

The reactions of 2,3,5-trichloro- and 2,5-dichloro-3-furfuryloxy-5-(2-methyl-3-furyl)-4,4-dimethoxycyclopent-2-en-1-ones with diethylamine or morpholine result in the decyclization of the 2-methylfuran substituent, giving the corresponding products in good yields.     

Specificity of the reaction of 2,3-dichloro-4,4-dimethoxy-5-(2-methylfuran-3-yl)cyclopent-2-en-1-one with amines

2,3-Dichloro-4,4-dimethoxy-5-(2-methylfuran-3-yl)cyclopent-2-en-1-one reacted with diethyl-and dipropylamines to give products of Ad_NE replacement of the chlorine atom at the vinylic C³ atom and substitutive opening of the furan ring with simultaneous deprotection of the dimethyl acetal moiety in the 2,3-dichlorocyclopentenone fragment.     

Theoretical study of the thermal rearrangement of chloromethylsilanes, and its mechanism

The thermal rearrangement reactions of chloromethylsilane, (chloromethyl)dimethylsilane, and (chloromethyl)vinylsilane have been studied by use of the density functional theory method at the B3LYP/6-311G(d, p) level. The structures of the reactants, transition states, and the products were determined and fully optimized. The geometries of the different stationary points and the harmonic vibrational frequencies were calculated at the same level. The results showed that thermal rearrangement of the chloromethylsilanes occurred via one pathway. The chlorine atom migrated from the carbon atom to the silicon atom, and the hydrogen atom migrated simultaneously from the silicon atom to the carbon atom through a double-three-membered-ring transition state, forming methylchlorosilane, trimethylchlorosilane, and vinylmethylchlorosilane. The energy barriers of the three rearrangements calculated at the B3LYP/6-311G(d, p) level were 217.4, 201.6, and 208.7 kJ mol^?1, respectively. The effects of alkyl substituents on silicon atom are discussed. Changes of thermodynamic functions, equilibrium constant, and reaction rate constant were calculated in accordance with Eyring transition-state theory over the temperature range 400–1,500 K.     

Stereoretentive O-to-C rearrangement of vinyl acetals: solvent cage effects as a stereocontrol element

The Lewis acid-mediated rearrangement of chiral vinyl acetals may be induced to provide the product of stereoretention using Me3Al and BF3.OEt2 in concert. The selectivities obtained in this reaction (86:14 to 96:4) are complementary to that observed when relying on oxocarbenium facial bias to control the newly formed stereocenter. Evidence is presented that this reaction occurs by tight ion-pair binding in the solvent cage. The relay of C-O bond stereochemistry to a C-C bond stereocenter via ionic intermediates is an addition to similar established methods such as the Claisen rearrangement.     

New captodative polyheterofunctionalized cyclopentenones from 2,3,5-Trichloro-4,4-dimethoxy-5-(2-methylfuran-3-yl)cyclopent-2-en-1-one and secondary amines

2,3,5-Trichloro-4,4-dimethoxy-5-(2-methylfuran-3-yl)cyclopent-2-en-1-one reacted with secondary amines to give unusual Ad_NE-substitution-fragmentation products, 5-[(1Z,2E)-1-acetyl-3-dialkylaminoprop-2-en-1-ylidene]-3-dialkylamino-2-chloro-4,4-dimethoxycyclopent-2-en-1-ones.     

Structural and solvent effects on the mechanism of base-induced rearrangement of epoxides to allylic alcohols

A combined experimental and computational study is presented which explores the influence of structure and solvent on the base-catalyzed isomerization of cyclopentene- and cyclohexene oxides. Cyclohexene oxide is known to rearrange via a syn beta-elimination in nonpolar solvents. Cyclopentene oxide instead undergoes alpha-elimination to a carbenoid intermediate in nonpolar solvents due to the unusual acidity of the alpha-proton, not because of an unfavorable conformation. In HMPA, cyclopentene oxide undergoes beta-elimination. To explore the origins of this mechanistic change, deuterium-labeled cis-4-tert-butylcyclohexene oxide was rearranged in HMPA and was found to react via anti beta-elimination, as presumably do cyclopentene oxide and other epoxides.     

Theoretical study of isoelectronic systems: Diazomethane,ketene and allene

All-electron SCF –LCAO –MO computations for diazomethane, ketene and allene are presented. The basis functions are contracted Gaussian orbitals. Theoretical results are discussed and related to available experimental data.     

Synthesis and mesomorphic properties of some cyclohex-2-en-1-one derivatives

Mesomorphic properties of cyclohex-2-en-1-ones belonging to 14 different chemical structural types are compared and discussed. They were prepared by condensation of Mannich salts with 2-substituted acetoacetates or benzyl methyl ketones or acetylacetone in the presence of potassium hydroxide.     

Crystal structures of 1,1,1-trifluoro-4-hydroxy-4-phenyl-but-3-en-2-one, 2,2,6,6-tetramethyl-3-hydroxy-hept-3-en-5-one, 2,2,6,6-tetramethyl-3-methylamino-hept-3-en-5-one and a study of the ability of these ligands to complex formation with metals

Crystal structures are determined (Bruker Nonius X8 Apex, 4K CCD-detector, λMoK _α, graphite monochromator, T 150 K and 293 K) for two β-diketones F₃CC(O)CH₂C(O)Ph (1) (space group P2₁/c, a = 7.0713(3)Å, b = 11.5190(6)Å, c = 11.3602(6) Å, β = 99.405(2)°, V = 912.90(8) ų, Z = 4), (CH₃)₃CC(O)CH₂C(O)C(CH₃)₃ (2) (space group Pbca, a = 11.5536(8) Å, b = 11.5796(10) Å, c = 17.2523(13) Å, V = 2308.1(3) ų, Z = 8) and a ketoimine (CH₃)₃CC(NCH₃)CH₂C(O)C(CH₃)₃ (3) (space group I4₁/a, a = 18.7687(6) Å, b = 18.7687(6) Å, c = 14.5182(6) Å, V = 5114.2(3) ų, Z = 16). All structures are molecular and comprise isolated molecules joined by van der Walls interactions. The substitution energy of a Na atom for a hydrogen atom in free ligands is calculated by the hybrid B3LYP quantum chemical method. A successful preparation of Na(I) chelates with ligands 1, 2 and failed attempts to prepare a complex with ligand 3 are in accordance with the calculations. Geometrical simulation of a copper(II) complex with ligand 3 reveals the overlap of CH₃ groups which hinders the complexation.     

Theoretical study on the reaction mechanism of vinyl radical with formaldehyde

A detailed computational study is performed on the radical-molecule reaction between the vinyl radical (C2H3) and formaldehyde (H2CO), for which only the direct hydrogen abstraction channel has been considered by previous and very recent theoretical studies. At the Gaussian-3//B3LYP/6-31G(d) and CBS-QB3 levels, the direct H-abstraction forming C2H4 + HCO has barriers of 3.9 and 4.7 kcal/mol, respectively. The addition barrier to form H2CCHCH2O has barriers of 2.8 and 2.3 kcal/mol, respectively. Subsequently, there are two highly competitive dissociation pathways for H2CCHCH2O: One is the formation of the direct H-extrusion product H2CCHCHO + H, and the other is the formation of C2H4 + HCO via the intermediate H2CCH2CHO. Surely, the released energy is large enough to drive the secondary dissociation of HCO to H + CO. Because the involved transition states and intermediates of the H2CCHCH2O evolution all lie energetically lower than the entrance addition transition state, the addition-elimination is more competitive than the direct H-transfer for the C2H3 + H2CO reaction, in contrast to previous expectation. The present results can be useful for future experimental investigation on the title reaction.     

A new and efficient chemoenzymatic route to both enantiomers of 4-hydroxycyclohex-2-en-1-one

[reaction: see text] A chemoenzymatic synthesis of both enantiomers of the pharmacologically interesting 4-hydroxycyclohex-2-en-1-one in three steps starting from 3-methoxycyclohex-2-en-1-one is described. Manganese(III) acetate-mediated acetoxylation followed by enzyme-mediated hydrolysis of alpha-acetoxy enone affords acetoxy enone 3 and hydroxy enone 4 with high enantiomeric excesses and in good yields. The reduction of the acetoxy and hydroxy enones furnished both enantiomers of 4-hydroxycyclohex-2-en-1-one in high enantiomeric excess.     

Theoretical study on the mechanism and kinetics for the ozonolysis of vinyl propionate

The O₃-initiated oxidation of vinyl propionate is studied using quantum chemistry calculations. Detailed and complete reaction mechanisms are presented which involve the formation of the primary ozonide (POZ), the subsequent decomposition of POZ, the secondary reactions of CH₃CH₂C(O)OCHO₂ (IM4) in the presence of H₂O or NO as well as the generation of the secondary ozonide (IM6). Based on the above PESs calculations, the Multichannel Rice–Ramsperger–Kassel–Marcus theory is employed to calculate the total and individual rate constants for major product channels. The rate constants and branching ratios of main products are obtained. The total rate constants are temperature dependent over the whole study temperature range (200–2,000 K), but pressure independent over the range of 0.01–10,000 Torr. In addition, the atmospheric lifetime is estimated in accordance with rate constants.     

Synthesis of substituted 1-trifluoromethyl and 1-perfluoroalkyl-3-(arylamino)prop-2-en-1-one: advances in the mechanism of Combes 2-trifluoromethyl and 2-perfluoroalkyl quinolines synthesis

We report a new synthesis and our study of the mechanism of formation of substituted 1-trifluoromethyl and 1-perfluoroalkyl-3-(phenylamino)prop-2-en-1-one starting from 3-(R-phenoxy)-3-perfluoroalkyl-prop-2-enals and arylamines. Reactivity study of the intermediates confirmed that 3-perfluoroalkyl-N,N′-diphenyl-1,5-diazapentadienes are the synthetic intermediates of the synthesis of 2-perfluoroalkylquinolines. The mechanism of the reaction of 1-trifluoromethyl and 1-perfluoroalkyl-3-(phenylamino)prop-2-en-1-one with POCl₃ was studied. To our knowledge this is the first detection and isolation of N,N′-diaryldiazapentadiene derivatives as intermediates in the Combes F-alkyl substituted quinoline synthesis starting from enaminoketones. Finally, we succeeded isolating and identifying unsymmetrically substituted 2-perfluorolakyldiazapentadiene.