1593772-16-7Relevant academic research and scientific papers
Elucidation of the reaction mechanism of ortho→α transmetalation reactions of alkyl aryl sulfone carbanions
Rehova, Lucie,Jahn, Ullrich
, p. 4610 - 4623 (2014)
The sulfonyl group, as an electron-accepting function, displays a strong acidifying effect on neighboring α-hydrogen atoms, leading to their deprotonation by bases. Recently, reversal of the metalation selectivity of α,γ-branched alkyl aryl sulfones was described, which instead undergo directed ortho-metalation with good regioselectivity, despite having a more acidic α-proton. Upon warming, a transmetalation to the α-carbanion proceeds; however, nothing is known about the course of this transmetalation. Here, a mechanistic study is presented that sheds light on the facility of the initial metalation and the subsequent transmetalation. Large kinetic isotope effects were observed for both the initial deprotonation and the ortho→α transmetalation, which strongly influence the initial metalation selectivity. The results of a kinetic investigation of the transmetalation and a crossover study indicate that a concerted intermolecular pathway, either from an aggregate or from a monomeric aryllithium, prevails. The potential involvement of a stepwise process via ortho,α-dilithium intermediates was investigated, but no hint of their involvement was found. Copyright
Lithium-titanium exchange of tertiary α-sulfonyl carbanions: Synthesis, structure, dynamics and reactivity of bis(1-sulfonylalkyl) titaniums
Hess, Thomas,Raabe, Gerhard,Gais, Hans-Joachim
, p. 7134 - 7147 (2015/03/04)
Lithium-titanium exchange of tertiary α-sulfonyl carbanions with ClTi(OiPr)3 and Cl2Ti(OiPr)2 in diethyl ether gave bis(1-sulfonylalkyl) titaniums and not the corresponding (1-sulfon-ylalkyl) titaniums. X-ray crystal structure analysis of di(iso-propoxy) bis[1-(phenylsulfonyl) cyclobutyl]titanium and di-(isopropoxy) bis[1-(phenylsulfonyl) isopropyl]titanium showed asymmetric distorted octahedral complexes, having hexaco-ordinate Ti atoms, two C-Ti bonds, four Ti-O bonds, and two four-membered Ti-O-S-Cα rings. According to 1H NMR spectroscopy bis(1-sulfonylcycloalkyl) titaniums are non-flux-ional at room temperature. This suggests that chiral bis(1-sulfonylalkyl) titaniums should be configurationally stable. The bis(1-sulfonylalkyl) titaniums are stable at room temperature towards β-H elimination. They selectively add to benzaldehyde in the presence of acetophenone but do not react with methyl iodide. The reaction of tertiary acyclic α-sulfonyl carbanions with ClTi(OiPr)3 in tetrahydrofuran (THF) gives different titanium derivatives with unspecified structures, which not only selectively react with benzaldehyde in the presence of acetophenone but are also alkylated by methyl iodide.
Divergent reactivity of alkyl aryl sulfones with bases: Selective functionalization of ortho-aryl and α-alkyl units enabled by a unique carbanion transmetalation
Rehova, Lucie,Cisarova, Ivana,Jahn, Ullrich
, p. 1461 - 1476 (2014/03/21)
The electron-accepting sulfonyl group exhibits a strong acidifying influence on neighboring α-H atoms. The Julia and related olefinations are based on this effect. Here a surprising reversal in the metalation selectivity of branched alkyl aryl sulfones is described. Such sulfones were found to initially undergo directed ortho-metalation with good regioselectivity, despite having a more acidic α-H atom. The structure of the alkyl unit profoundly, but predictably, influences the regioselectivity of the attack of the base. In β- and γ-branched ortho-(alkylsulfonyl)aryllithiums a transmetalation to the α-carbanion proceeds only upon warming. Correspondingly generated ortho- or α-carbanions were then selectively applied thus permitting access to synthetically interesting compound classes. An unusual lithiation selectivity and subsequent transfer of the metal upon warming was observed for various branched alkyl phenyl sulfones. This divergent reactivity was used to prepare substituted aryl sulfones as well as olefins by application of the Julia reaction. Copyright
Divergent Reactivity of Alkyl Aryl Sulfones with Bases: Selective Functionalization of ortho-Aryl and α-Alkyl Units Enabled by a Unique Carbanion Transmetalation
?ehová, Lucie,Císa?ová, Ivana,Jahn, Ullrich
, p. 1461 - 1476 (2015/10/05)
The electron-accepting sulfonyl group exhibits a strong acidifying influence on neighboring α-H atoms. The Julia and related olefinations are based on this effect. Here a surprising reversal in the metalation selectivity of branched alkyl aryl sulfones is described. Such sulfones were found to initially undergo directed ortho-metalation with good regioselectivity, despite having a more acidic α-H atom. The structure of the alkyl unit profoundly, but predictably, influences the regioselectivity of the attack of the base. In β- and γ-branched ortho-(alkylsulfonyl)aryllithiums a transmetalation to the α-carbanion proceeds only upon warming. Correspondingly generated ortho- or α-carbanions were then selectively applied thus permitting access to synthetically interesting compound classes.
