692-48-8Relevant articles and documents
A spontaneous fragmentation: From the Criegee zwitterion to coarctate Mobius aromaticity
Berger, Christian,Bresler, Christian,Dilger, Ulrich,Geuenich, Daniel,Herges, Rainer,Roettele, Herbert,Schroeder, Gerhard
, p. 1850 - 1853 (2007/10/03)
The extremely fast fragmentation of the spiroozonides prepared from formaldehyde O-oxide and three-membered ring ketones proceeds via the coarctate transition state 1. The ozonides decompose at temperatures as low as -90°C to form carbon dioxide, alkene/alkyne, and formaldehyde (the topology of the structure of 1 is depicted on the right). The mechanism is in accordance with the rules for the stereochemical course of coarctate reactions.
cis-2,3-Di-tert-butylcyclopropanones
Sorensen,Sun
, p. 1030 - 1040 (2007/10/03)
The preparation of the strained cis-2,3-di-tert-butylcyclopropanone 2 from the acyclic compound, α,α′-dibromodineopentyl ketone 1, using a previously reported methodology, is dramatic evidence of both the existence of oxyallyl intermediates in the mechanism of this reaction, and of the integrity with which oxyallyls ring-close to cyclopropanones by a disrotatory route. Because of the bulky cis substituents, cyclopropanone 2 exhibits a number of unusual spectroscopic features (as compared to the trans isomer 5). With the aid of ab initio calculations on 2 and 5, it can be shown that the C2 - C3 bond in 2 interacts with the carbonyl π-orbitals, thus causing the carbonyl oxygen to bend 12° out of the plane; this interaction is absent in 5 and the latter has a planar carbonyl group. As with other cyclopropanones, 2 can be photochemically decarbonylated. This process itself appears to be stereospecific even though highly strained alkenes are produced. Cyclopropanone 2 is thermally rearranged to the trans isomer 5 and the kinetics for this are reported; our favoured mechanism involves oxyallyl intermediates. Other reactions of 2 also appear to proceed through these oxyallyl species; for example, alcohols initially add to 2 to give α-alkoxy enols, solutions of 2 enter into very facile diene cycloadditions, and the dimerization of neat 2 also appears to involve these oxyallyl species.
Heterodiene cycloadditoins of C2 symmetric 4,5-disubstituted ketene acetals: the nett asymmetric conjugate addition of recyclable acetic ester enolate equivalents to an activated enone
Wallace, Timothy W.,Wardell, Ian,Li, Ke-Dong,Leeming, Peter,Redhouse, Alan D.,Challand, S. Richard
, p. 2293 - 2308 (2007/10/02)
Heterodiene cycloadditions of 3-formylchromone 2 to a series of ketene acetals 1 derived from C2 symmetric 1,2-diarylethane-1,2-diols are diastereoselective.From (S,S)-1,2-di(o-tolyl)ethane-1,2-diol 6c the major cycloadduct 3c was isolated by crystallization and transformed by acid-catalysed methanolysis into (S)-methyl 4-oxo-3,4-dihydro-2H-1-benzopyran-2-ylacetate 5, together with the original 1,2-diol 6c which could be recycled.The structures of two cyclic carbonates 22a and 22c were determined by X-ray diffraction and used as models in seeking a mechanistic rationale for the stereoselective cycloadditions of the analogous ketene acetals 1a and 1c.
Preparation of tert-Butyl-Capped Polyenes Containing up to 15 Double Bonds
Knoll, Konrad,Schrock, Richard R.
, p. 7989 - 8004 (2007/10/02)
7,8-Bis(trifluoromethyl)tricyclo2,5>deca-3,7,9-triene (TCDT) can be ring-opened in a controlled manner by W(CH-t-Bu)(NAr)(O-t-Bu)2 (Ar = 2,6-C6H3-i-Pr2) to give living oligomers from which the metal can be removed in a Wittig-like reaction with pivaldehyde or 4,4-dimethyl-trans-2-pentenal.Heating the oligomer yields a distribution of tetr-butyl-capped polyenes, (t-Bu)(CH=CH)n(t-Bu), where n is odd if pivaldehyde is used in the cleavage reaction or even if 4,4-dimethyl-trans-2-pentenal is used.Mixtures of odd and even polyenes have been analyzed byreserved-phase HPLC methods, and those having as many as 13 double bonds have been isolated by column chromatography on silica gel under dinitrogen at -40 deg C and characterized by (1)H and (13)C NMR and UV-vis studies.The 17-ene has been observed by HPLC.Polyenes containing more than 17 double bonds are relatively unstable under the reaction and subsequent isolation conditions; those containing between 11 and 15 double bonds decompose thermally progressively more readily.The initial isomer in the odd-ene series has largely the trans(cis,trans)x geometry as a result of stereospecific trans initiation, stereoselective trans propagation, stereospecific trans cleavage, and stereospecific cis retro-Diels-Alder reactions.The even-ene series is more complex since the Wittig-like reaction involving 4,4-dimethyl-trans-2-pentenal is not selective.UV-vis and (13)C and (1)H NMR data have been collected and analyzed in detail for the trans(cis,trans)x isomers for x = 1-5 (up to 11 double bonds) and for the odd and even all-trans forms containing up to nine double bonds.Extrapolation of a plot of the energy of the 1Bu 1Agg(0-0) transition versus 1/n (for up to the 13-ene) predicts that the HOMO-LUMO gap will be 1.79-1.80 eV for an infinite all-trans-polyene; in carbon disulfide it will be 1.56 eV.For the trans(cis,trans)x forms the 1Bu 1Agg(0-0) energy gap is predicted to be 1.95 eV for an infinite polyene in a mixture of acetonitrile, dichloromethane, and water (90:5:5).The ease of thermal cis-to-trans isomerization (ultimately to the all-trans form) correlates directly with chain length, isomerization to the all-trans form being especially facile for the 13-ene and beyond.The all-trans-polyenes are significantly less soluble than forms that contain one or more cis double bonds, although cross-linking cannot be ruled out as a contributor to insolubility for polyenes longer than the 13-ene.The retro-Diels-Alder reaction in the first unit away from the metal in living polyTCDT is accelerated 10 times relative to that in the second unit away from the metal.Heating polyTCDT gives living polyenes that are stable at 50 deg C for 45 min in solution; no benzene is formed.
Rotational Barriers of Strained Olefines
Doering, William v. E.,Roth, Wolfgang R.,Bauer, Frank,Breuckmann, Rolf,Ebbrecht, Thomas,at al.
, p. 1263 - 1276 (2007/10/02)
For the olefins 1-8 heats of formation have been derived from heats of hydrogenation and force-field calculations, respectively.From the kinetics of their geometrical isomerisation the corresponding values for the transition states were obtained.The rotational barriers, which vary by nearly 30 kcal/mol, can be described by a unique torsional potential (65.9 +/- 0.9 kcal/mol), which is independent of the degree of substitution, if a correction is made for the steric energy contribution in the ground- and transition-states. - Key Words: Rotational barriers / Olefins, strained / Heat of Hydrogenation / Force-field calculation
Synthesis of Ethylenes with Acyclic Quaternary Carbons by Dehydration of Neopentyl Alcohols. Application of the 2-D INAPT Technique
Drake, C. A.,Rabjohn, Norman,Tempesta, Michael S.,Taylor, Richard B.
, p. 4555 - 4562 (2007/10/02)
Di- and triquaternary ethylenes (5, 12 and 7, 19, Scheme I) have been synthesized by dehydration of sec- and tert-neopentyl alcohols (4, 11 and 6, 18) without rearrangement.It is thought that steric factors determine the structures of the products.The intermediate imines 2 and 14, from the reaction of nitriles 1 and 13 with t-C4H9Li, may be hydrolyzed only in the first case to ketones (3).More highly substituted ketones (10 and 16) were obtained by the reaction of t-RMgX (9) or (CH3)3CMgCl with 3,3-dialkyl and 2,3,3-trialkyl acid chlorides (8 and 15).Ketones 3 and 10 were reduced by LiAlH4 to secondary carbinols 4 and 11.The tertiary carbinols 6 were prepared from 3 by treatment with t-C4H9Li.The more hindered ketones 16 failed to add t-C4H9Li, but were reduced to secondary alcohols 18, instead of the desired tertiary alcohols 17.The carbinols 4, 6, 11, and 18 were dehydrated by heating with KHSO4.The 2-D INAPT NMR technique was used to establish the stereostructure of 19 by measuring the long-range heteronuclear coupling constants about the ene.
THERMAL REACTIONS OF CYCLOBUTANEDIONES
Rubin, Mordecai B.,Harel, Yaakov
, p. 5373 - 5376 (2007/10/02)
Thermolysis of cyclobutanediones in hydrocarbon solvents shows marked dependence on structure and may involve bis-decarbonylation to olefins, monodecarbonylation with rearrangement to cyclopentenone derivatives, or rearrangement without loss of carbon monoxide.
Effect of Metal Loading and Triphenylphosphine on Product Selectivities in the Hydrogenation of Di-tert-butylacetylene and 3-Hexyne over Palladium/Alumina
Siegel, Samuel,Hawkins, James Adrian
, p. 1638 - 1640 (2007/10/02)
The effect of triphenylphosphine and metal loading and/or dispersion on the product distributions from di-tert-butylacetylene indicates that the surface structure of the metal particles also may affect stereospecificities by promoting different catalytic mechanisms at different sites.
trans-2,3-Di-tert-butylthiirane 1,1-Dioxide and 2,5-Di-tert-butyl-2,5-dihydro-1,3,4-thiadiazole 1,1-Dioxides from tert-Butyldiazomethane and Sulfur Dioxide. Solvent Effects and Mechanisms of the Staudinger-Pfenninger-Reaction
Quast, Helmut,Kees, Frieder
, p. 787 - 801 (2007/10/02)
When allowed to react with sulfur dioxide tert-butyldiazomethane formed not only trans-di-tert-butylthiirane 1,1-dioxide (3) but also the diastereomeric 2,5-dihydro-1,3,4-thiadiazole 1,1-dioxides 7e which under base-catalysis rearranged to the 2,3-dihydro-1,3,4-thiadiazole 1,1-dioxide 11.The structures were deduced from IR, UV, and 1H-NMR-spectra, and from the products obtained after loss sulfur dioxide.Whereas increase of the solvent polarity favoured 3 over 7e, the diastereomer ratio cis-7e/trans-7e remained virtually unaffected.The ratio of thiirane 1,1-dioxide 3 to dihydrothiadiazole 1,1-dioxides did not depend on whether the intermediate tert-butylsulfene 6e had been generated from 5e and sulfur dioxide or from 2,2-dimethylpropane sulfonylchloride (14) and triethylamine.In contrast to reports in the literature, the reaction of the phenyldiazoalkanes 5f and 5h with sulfur dioxide afforded cis/trans ratios of the thiirane 1,1-dioxides 9f and 9h, respectively, which were only slightly influenced by the solvent.Apparently, the dihydrothiadiazole 1,1-dioxides 7 and hence their decomposition products, the azines 8 (as far as these do not arise from the direct decomposition of the diazo compounds), are the result of a cycloaddition between the diazoalkane 5 and the sulfene 6.In contrast, the thiirane 1,1-dioxides 9 seem to originate via the zwitterions 20 the formation of which is favoured over the cycloaddition by solvents of high polarity, by the presence of aryl substituents at the sulfene, as well as by the lack of alkyl groups.The dichotomy in the behaviour of sulfenes towards diazoalkanes can be traced back to the existence of two low-lying sulfene MO's, only one of which exhibits ?-symmetry.
