Direct Transformations of Ketones to γ-Unsaturated Thiols via [2,3]-Sigmatropic Rearrangement of Allyl Sulfinyl Carbanions:  A Combined Experimental and Computational Study

Abstract

The reaction of a series of ketones with dimsylsodium in dimethyl sulfoxide resulting in the formation of gamma-unsaturated thiols was studied experimentally. [2,3]-Sigmatropic rearrangements of beta-unsaturated sulfinyl carbanions are involved at the key step of those transformations. DFT computations at the B3LYP/6-31+G level indicated that such rearrangements, as well as some typical [2, 3]-sigmatropic rearrangements, e.g., thermal rearrangements of allyl sulfoxides and Wittig rearrangements of sulfur ylides and lithiated allyloxy methyl anions, are concerted and moderately synchronous processes. Negative (diatropic) nucleus-independent chemical shifts (NICS) and high diamagnetic susceptibility exaltations indicate that the transition structures of these [2,3]-sigmatropic migrations are aromatic.

From Allylic Sulfoxides to Allylic Sulfenates: Fifty Years of a Never-Ending [2,3]-Sigmatropic Rearrangement

“…However, the reaction with o -aminoacetophenone 166 afforded hydroxymethyl derivative 168 as the major product, presumably by vinyl-to-allyl isomerization of the reaction intermediate, and [2,3]-sigmatropic rearrangement followed by aromatization . This rearrangement was used for the epimerization of vinyl cyclobutanols, and it was mentioned in the optimization of a related rearrangement involving allyl sulfinyl carbanions …”

“…126 This rearrangement was used for the epimerization of vinyl cyclobutanols, 127 and it was mentioned in the optimization of a related rearrangement involving allyl sulfinyl carbanions. 128 Raghavan et al explored the reactivity of α-chloro sulfides bearing additional oxygen substituents with organozinc reagents to afford a variety of substrates related to 169 (Scheme 30) with good diastereoselectivities in most cases. Oxidation and sigmatropic rearrangement produced 1,4-diol derivatives 170 in excellent yields.…”

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“…Calculations (HF/3-21G and B3LYP/6-31G*) support these conclusions, as well as reveal the importance of the pentamethylene tether in lowering the activation energy of [1,5] 2 in DMSO, to give primarily gunsaturated thiols. 75 A computational analysis of this rearrangement at the B3LYP/ 6-31+G* level of theory finds that rearrangement of the bare anion is exothermic by 26-29 kcal mol 21 , with a barrier of 0.3-5 kcal mol 21 . Rearrangement is concerted and moderately synchronous, as is the case for other [2,3] rearrangements.…”

The synthesis of thiols, selenols, sulfides, selenides, sulfoxides, selenoxides, sulfones and selenones

“…8 Finally, the direct preparation of γ-unsaturated thiols from ketones using methanesulfinyl carbanion in DMSO has been reported. 9 The reaction has been shown to proceed via the [2,3]sigmatropic rearrangement of intermediate β-unsaturated sulfinyl carbanions (Scheme 7).…”