2484-99-3Relevant academic research and scientific papers
Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 13.1 Extrusion of Ph3P from sulfinyl ylides and reactivity of the resulting sulfinyl carbenes
Aitken, R. Alan,Drysdale, Martin J.,Ryan, Bruce M.
, p. 3345 - 3348 (2007/10/03)
Six α-sulfinyl phosphorus ylides 6 have been prepared and are found upon flash vacuum pyrolysis at 500°C to undergo mainly extrusion of Ph3P to give thioesters, presumably by 1,2-oxygen transfer in the initially formed sulfinyl carbenes; for α-arylsulfinyl ylides loss of Ph3PO to give additional products is also observed.
Stereochemistry of the [4 + 2] cycloaddition of diarylselenoketones with conjugated dienes
Wilker, Stefanie,Erker, Gerhard
, p. 10922 - 10930 (2007/10/03)
The ylides Ph3P=CAr1Ar2 1a-g (Ar = C6H5, p-C6H4Cl, p-C6H4F, m-C6H4CF3, p-C6H4OCH3, p-C6H4-CH3) were treated with elemental selenium (～80°C) to give the corresponding selenoketones Se=CAr1Ar2 2 by Staudinger-chalcogenation. Their reaction with trans,trans-2,4-hexadiene proceeds completely stereospecifically to yield the 2,2-diaryl-3,6-dihydro-cis-3,6-dimethyl-2H-selenapyrans 3. In contrast, the reactions of the selenoketones 2 with cis,trans-2,4-hexadiene proceeds stereoselectively, also giving the dihydro-cis-dimethyl-2H-selenapyrans 3 as the major products, now admixed with small amounts of the dihydro-trans-dimethyl-2H-selenapyran isomers 4. The [4 + 2] cycloaddition of 2 with cis,trans-2,4-hexadiene proceeds stereospecifically, however, when carried out at a pressure of 12 kbar, now yielding 4 as the major products along with the corresponding tetraarylethenes 8. Along with the results of additional mechanistic studies (determination of solvent and substituent effects) it can be concluded that diarylselenoketones are likely to react by means of a concerted [4 + 2] cycloaddition with very reactive conjugated dienes (such as trans,trans-2,4-hexadiene), whereas a stepwise mechanism, resulting in diene cis/trans-isomerization with subsequent mechanistic "leakage" to the concerted pathway, appears to be preferred when a much less reactive conjugated diene such as cis,trans-2,4-hexadiene is employed. The reaction of the corresponding diarylthioketones 5a-g with trans,trans- and cis,trans-2,4-hexadiene, respectively, shows an analogous behavior.
Elimination Reactions of Alkanesulfenyl Derivatives: Effect of Structure on Reactivity in Thioketone-Forming Eliminations of Diarylmethyl Thiosulfonates
Kice, John L.,Weclas, Ludmilla
, p. 32 - 39 (2007/10/02)
The reaction of a group of diarylmethyl arenethiosulfonates, ArAr'CHSSO2Ar'' (2), with (a) two alkoxide ions (i-PrO- and MeO-), (b) a series of secondary and tertiary amines of differing base strength, and (c) phenoxide ion has been examined.For each system both the overall rate of disappearance of 2 and the fraction (αelim) converted to thioketone were determined.Salient results are as follows: (1) The ρ values for thioketone-forming elimination of ArAr'CHSSO2C6H4CH3-p with either isopropoxide (+3.4) or piperidine (+3.5) are large and positive, while theρ value associated with variation of the substituent in Ar'' in the elimination of Ph2CHSSO2Ar'' with i-PrO- is quite modest (+1.3). (2) The Broensted β for the elimination reaction of p-nitrobenzhydryl p-toluenethiosulfonate with the series of amines is close to +1.0. (3) While plots of the elimination rate constant (kelim) vs. for any of the amine-induced elimination in amine-amineH+ buffers are linear, plots of kelim vs. -> for the phenoxide-induced elimination in PhO--PhOH buffers very pronounced downward curvature (Figure 4).These various results can be explained by assuming that the different eliminations proceed by different variants of an ElcB mechanism: for the elimination involving amines and 2 a reversible (ElcB)ion pr mechanism (eq 13) is suggested; in the elimination with phenoxide ion the reaction proceeds by an ordinary (ElcB)reversible mechanism (eq 9, ki>kii); in the elimination involving isopropoxide the mechanism becomes (ElcB)irreversible (eq 9, k-iii).Comparison of selected data on the rates of thioketone-forming eliminations of 2 with amines with data obtained previously (ref 6) on the rates of sulfene-forming eliminations of aralkyl α-disulfones with amines indicates that an arylalkanesulfonyl compound undergoes elimination approximately 300 million times faster than the equivalently substituted arylalkanesulfenyl derivative.
Photochemical Oxidation of Thioketones: Steric and Electronic Aspects
Ramnath, N.,Ramesh, V.,Ramamurthy, V.
, p. 214 - 222 (2007/10/02)
Oxidation of diaryl, aryl alkyl, and dialkyl thioketones by singlet oxygen generated via self-sensitization and other independent methods yielded the corresponding ketone and sulfine in varying amounts.A zwitterionic/diradical intermediate arising out of the primary interaction of singlet oxygen with the thiocarbonyl chromophore is believed to be the common intermediate for the ketone and sulfine.While closure of the zwitterion/diradical to give 1,2,3-dioxathietane would lead to the ketone, competing oxygen elimination is believed to lead to the sulfine.This partitioning is governed by steric and electronic factors operating on the zwitterionic/diradical intermediate.
