6004-60-0Relevant academic research and scientific papers
Diazo chemistry controlling the selectivity of olefin ketonisation by nitrous oxide
Hermans, Ive,Moens, Bart,Peeters, Jozef,Jacobs, Pierre,Sels, Bert
, p. 4269 - 4274 (2008/09/19)
The thermal reaction of olefins with nitrous oxide was recently put forward as a promising synthetic ketone source. The 1,3-dipolar cycloaddition of N 2O to the C=C double bond, forming a 4,5-dihydro-[1,2,3]oxadiazole intermediate, was predicted to be the first elementary reaction step. This oxadiazole can subsequently decompose to the desired carbonyl product and N 2 via a hydrogen shift. In this contribution, Potential Energy Surfaces are constructed at the reliable G2M level of theory and used to evaluate thermal rate constants by Transition State Theory. Compelling theoretical and experimental evidence is presented that an oxadiazole intermediate not only can undergo a hydrogen shift, but eventually also a methyl- or even an alkyl-shift. Special emphasis is also given on a hitherto neglected decomposition of the oxadiazole via a concerted C-C and N-O cleavage. For some substrates, such as internal olefins, this diazo route is negligibly slow, compared to the ketone path, leaving no marks on the selectivity. For cyclopentene the diazo cleavage was however found to be nearly as fast as the desired ketone route. However, the diazo compound, viz. 5-diazopentanal, reconstitutes the oxadiazole much faster upon ring-closure than it is converted to side-products. Therefore, a pre-equilibrium between the diazoalkanal and the oxadiazole is established, explaining the high ketone yield. On the other hand, for primary alkenes, such a concerted C-C and N-O cleavage to diazomethane is identified as an important side reaction, producing aldehydes with the loss of one C-atom. For these substrates, the bimolecular back-reaction of the C n-1 aldehyde and diazomethane is too slow to sustain an equilibrium with the oxadiazole; diazomethane rather reacts with the substrate to form cyclopropane derivatives. The overall selectivity is thus determined by a combination of H-, methyl- or alkyl-shift, and the eventual impact of a diazo cleavage in the oxadiazole intermediate. the Owner Societies.
Trans dialkoxylation of cyclic alkenes: A Prevost-type reaction
Schauble, J. Herman,Trauffer, Edward A.,Deshpande, Prashant P.,Evans, Robert D.
, p. 1333 - 1339 (2007/10/03)
Reaction of anhydrous silver perchlorate, sym-collidine, and iodine (2:1:1 molar ratio) with cyclic alkenes and an excess of an alcohol in CH 2Cl2 affords trans-1,2-dialkoxycycloalkanes in high yields and purity. The reaction occurs via initial formation of the trans-iodoethers, which undergo Ag-assisted iodide abstraction to give the trans-diethers. Georg Thieme Verlag Stuttgart.
New oxidative transformations of alkenes and alkynes under the action of diacetoxyiodobenzene
Yusubov,Zholobova,Filimonova,Chi, Ki-Whan
, p. 1735 - 1742 (2007/10/03)
Treatment of alkenes and alkynes with diacetoxyiodobenzene activated by mineral and organic acids predominantly results in oxidative rearrangement. 1,4-Diphenylbutadiene in MeOH gives 3,4-dimethoxy-1,4-diphenylbut-1-ene.
Liquid phase oxidation of alkenes with nitrous oxide to carbonyl compounds
Starokon,Dubkov,Babushkin,Parmon,Panov
, p. 268 - 274 (2007/10/03)
A variety of substrates including linear, cyclic, heterocyclic alkenes and their derivatives were tested in the liquid phase non-catalytic oxidation with nitrous oxide (N2O). The structure and composition of the alkenes have a significant effect on the reaction selectivity. With many alkenes, N 2O oxidation provides a selective way for the preparation of carbonyl compounds. The generation of carbene (or diazomethane) species is a remarkable feature of the oxidation of terminal alkenes.
Asymmetric synthesis of (S)-1-methyl-2-cyclohexen-1-ol, a constituent of the aggregation pheromone of Dendroctonus pseudotsugae
Hamon, David P. G.,Tuck, Kellie L.
, p. 4829 - 4835 (2007/10/03)
1-Methyl-2-cyclohexen-1-ol has been prepared by a three step synthesis from 1-methylcyclohexene, in greater than 94% e.e., via a 'merged substitution-elimination reaction' between NaSePh and 2-methyl-2- hydroxycyclohexyl p-toluenesulphonate. (C) 2000 Elsevier Science Ltd.
Clemmensen Reduction. XI. Fragmentation Reactions of Some 3-Acetylcycloalkanones
Bailey, Karen E.,Davis, Brian R.
, p. 1827 - 1834 (2007/10/03)
Clemmensen reduction of a series of 3-acetylcycloalkanones yields, as the major product, an acyclic unsaturated ketone, the product of fragmentation.Some normal carbonyl-methylene reduction also occurs.A mechanistic rationale for the fragmentation is advanced.
STEREOCHEMICAL EFFECTS IN THE GAS-PHASE PINACOL REARRANGEMENT OF CIS- AND TRANS-1-METHYLCYCLOHEXANE-1,2-DIOL.
Cecchi, Patrizio,Cipollini, Romano,Pizzabiocca, Adriano,Renzi, Gabriele,Speranza, Maurizio
, p. 4847 - 4856 (2007/10/02)
The gas-phase pinacol rearrangement of cis and trans-1-methyl-1,2-cyclohexanediols, promoted by D3(+) and CnH5(+) (n= 1,2), was studied by the radiolytic method in the pressure range 100-760 Torr.Under all conditions, 2-methyl-cyclohexanone is the predominant product, arising from both substrates via different pinacol rearrangements and successive fast isomerisation of the corresponding primary intermediates, e,g, O-protonated 1-methyl-1-cyclopentanecarboxaldehyde.This conclusion is based from kinetic analysis of competition experiments with pinacol as reference substrate, carried out at high pressure (760 Torr) with or without added base (NMe3, 3 Torr), showing that the pinacol rearrngement rates are markedly dependent on the stereochemical features of the diol.Accordingly, the trans diol rearranges more rapidly than the cis isomer, which in turn isomerizes faster than pinacol, indicating that anti-periplanar CH2 migration to the vicinal tertiary C-OH2(+) center in trans (k2) is over five times faster than H migration in cis (k3).Analysis of the relative migrating ability of the different CH2 moieties in trans (k2 > k1) allowed exclusion of appreciable anchimeric assistance in these gas-phase pinacol rearrangements.The results are compared with revelant gas-phase data with those concerting the same substrates in acidic solution.
GAS-PHASE ACID-INDUCED RING OPENING IN SUBSTITUTED 1,2-EPOXYCYCLOHEXANES
Crotti, Paolo,Macchia, Franco,Pizzabiocca, Adriano,Renzi, Gabriele,Speranza, Maurizio
, p. 739 - 746 (2007/10/02)
The nature and the stereoisomeric distribution of the neutral products obtained from the gas-phase attack of radiolytically formed Broensted +, CH5+, C2H5+, and t-C4H9+> and Lewis +, t-C4H9+, and CH3FCH3+> acids on several substituted 1,2-epoxycyclohexanes have been investigated under different experimental conditions.Isolation and identification of the neutral substituted products allowed us to confirm previous indications about highly regio- and stereo-selective cationic nucleophilic displacements on these substrates occuring in the gas-phase with complete inversion of the configuration at the reaction centre (the α-C atom).In some cases, extensive acid-induced isomerization became the only observable pathway.The relative extent of the competiting substitution and isomerization was found to depend on several factors, including the structural features and internal energy of the oxonium derivative of the epoxy substrate.The results obtained from the present gas-phase experiments are discussed in relation to gas-phase and solution studies.
Malonate Anion Induced Favorskii-Type Rearrangement. Reaction of Cyclic α-Halo Ketones with Sodiomalonates
Sakai, Takashi,Amano, Eiichiro,Kawabata, Akifumi,Takeda, Akira
, p. 43 - 47 (2007/10/02)
The reaction of 2-chlorocyclohexanone (1b) with ethyl sodiomalonate in benzene at 0-25 deg C gave 6-bicyclohexan-6-ol (4c), the Favorskii-type intermediate, in 49percent yield, in place of the substitution product ethyl C-(2-oxocyclohexyl)malonate (3).Derivatives of bicycloheptan-7-ol (4a,b) and those of bicyclohexan-6-ol (4d,e) were also obtained in good yields by similar means.Compound 4c was transformed into 3 readily by heating with 0.05 equiv of NaH in benzene.The hydrolysis of 4a-d with 0.2 N NaOH followed by pyrolysis at 110-120 deg C gave the ring-contracted β-keto esters 9a-d.Pyrolysis after the hydrolysis with 2N NaOH gave the corresponding ketones 11a-d in good yields.Oxidation of 4c with CrO3 and HClO4 afforded ethyl C-(2-hydroxycyclopentanecarbonyl)malonate (14) in 45 percent yield.Treatment of 4c with Br2 gave ethyl C-(1-bromocyclopentanecarbonyl)malonate (18) in 64 percent yield.
Oxidation of Alkenes by Iodine Tris(trifluoroacetate). On the cis-Effect of the Trifluoroacetate Group in Oxidations
Buddrus, Joachim,Plettenberg, Horst
, p. 1494 - 1506 (2007/10/02)
Iodine tris(trifluoroacetate) oxidizes alkenes to α-glycol bis(trifluoroacetates) (eq. (1) and tab. 1).By-products are acylals emerging out of a 1,2-shift (eq. (3)). 1,2-Disubstituted alkenes are mainly transformed into cis-glycol derivatives and tri- and tetrasubstituted alkenes to cis/trans mixtures.The oxidations proceed via 2-acyloxy-1,3-dioxolanes, formerly postulated by Winstein et al. as intermediates in similar oxidations, but only now isolated (comp. 3) and examined by NMR and rearranged to the corresponding α-glycols (3 -> 5).A similar reaction course isproposed for certain other alkene oxidations known from literature, in which a trifluoroacetate group is involved and which proceed under cis-addition (table 3).
