Configurational Stability of Optically Active Dichloromethyl p‐Tolyl Sulfoxide and Its Anionic Species: Experimental and Theoretical Study

Abstract

Racemization of optically active dichloromethyl p-tolyl sulfoxide took place at −78 • C in the presence of potassium bis(trimethylsilyl)amide (KHMDS), while the same racemization did not occur under reflux in toluene in the absence of KHMDS. Density functional theory calculations suggested that the pyramidal inversion at the sulfur center was unlikely to be involved in the racemization mechanism. An anionic species of the sulfoxide was found to be gradually converted into chlorobis(p-tolylsulfinyl)methane and dichlorocarbene. We propose a racemization mechanism mediated by achiral potassium p-toluenesulfenate and chloro(p-tolylsulfinyl)methylene. C 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:131-137, 2013; View this article online at wileyonlinelibrary.com.

Cooperative Binding of SO2 under M–O and C–S Bond Formation in a Rhenium(I) Complex with Activated Amino- or Iminopyridine Ligand

“…Reversible equilibration with similar activation barriers were also observed for FLP–SO 2 adducts for epimerization at sulfur . In comparison, chiral inversion at trisubstituted pyramidal sulfur centers, which is not associated with the presence of additional auxiliaries, usually proceeds with higher inversion barriers with respect to 2 , as demonstrated mainly for sulfoxides. − In this regard, a rather small entropy of activation (Δ S # ≈ 0) can be indicative of a nondissociative inversion about the S atom (pyramidal inversion) . A few sulfinate esters were reported to rearrange via a reversible dissociation-recombination process.…”

Investigation of Functionalized α‐Chloroalkyllithiums for a Stereospecific Reagent‐Controlled Homologation Approach to the Analgesic Alkaloid (−)‐Epibatidine

“…By contrast, identical treatment of homopropargyl sulfoxide syn-H-24 b resulted exclusively in elimination and gave (E)-enyne H-42 in > 95 % yield (E/Z = 96:4). Upon further study, it was discovered that partial racemization ( 15 %) can accompany the LDA (or LiHMDS)-mediated epimerization of syn-H-24 d. [33] This unwelcome phenomenon was avoided by using either NaHMDS or KHMDS instead of a lithium amide base. Of these two bases, the sodium amide provided superior diastereoselectivity and it should be regarded as optimal for the synthesis of nonracemic anti chlorosulfoxides.…”