Self-induced diastereoselective oxidation of vinyl sulfoxides bearing a chiral hydroxy group as a way of preparation of optically active sulfinyl dienophiles and their use in the asymmetric Diels-Alder reactions to cyclopentadiene

Lucchi, Ottorino De; Lucchini, Vittorio; Marchioro, Carla; Valle, G.; Modena, G.

doi:10.1021/jo00359a014

Cited by 119 publications

(27 citation statements)

References 7 publications

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“…Reduction with lithium aluminum hydride gave hydroxythiol 16 as a 5:1 mixture of the endo and exo diastereomers, which were separated by column chromatography (21). Alkylation of the endo-hydroxythiol with phenacyl chloride under basic conditions afforded phenacyl sulfide 17, which was the precursor of thioaldehyde 13.…”

Section: Resultsmentioning

confidence: 99%

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications

Aggarwal

Charmant

Dudin

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Bridged bicyclic sulfide 1 was originally found to provide high levels of asymmetric induction in sulfur ylide-mediated epoxidations. This sulfide possesses chirality in the [2.2.1] thioether moiety and the [2.2.1] camphor-derived carbocyclic moiety. To determine whether the optimal sulfide had been used, a diastereomer of sulfide 1 in which the stereochemistry of the [2.2.1] carbocycle was reversed (sulfide 5) was prepared and studied as an epoxidation catalyst. This diastereomer gave considerably lower levels of asymmetric induction than the original sulfide 1. From computational and x-ray studies it was found that sulfide 5 gave rise to a more hindered ylide, which reacted more reversibly with aldehydes leading to lower enantioselectivity. Conditions that reduced reversibility were also tested and high enantioselectivities were returned for sulfide 5 (similar to sulfide 1). The implications for the synthesis of chiral sulfides for asymmetric epoxidations are discussed.T he reaction of sulfur ylides with carbonyl compounds to give epoxides (1-8) provides a complementary method with oxidation of alkenes (9-12) for the preparation of these valuable synthetic intermediates. Although sulfur ylide reactions have traditionally operated with stoichiometric amounts of sulfonium salts, we have recently reported a user-friendly, catalytic, and asymmetric process for epoxidation of carbonyl compounds that operated under neutral conditions by using tosylhydrazone sodium salts as diazocompound precursors and substoichiometric amounts (5 mol% in many cases) of chiral sulfide 1 and metal catalyst (Scheme 1) (13-16). This chiral sulfide could be recovered in high yield and reused without any loss of asymmetric induction. A broad range of aldehydes, including aromatic, aliphatic, and certain ␣,␤-unsaturated aldehydes, could be converted into the corresponding epoxides in generally high yield with high levels of enantioselectivity and diastereoselectivity (17). Sulfide 1 could also be used in a stoichiometric variant of this process, which allows access to epoxides that are difficult to form using the catalytic protocol (18).We have recently proposed a model to explain the high enantioselectivity in this system based on both experimental and computational data (Scheme 2) (19). The high enantioselectivity observed resulted from ylide 2A being strongly favored over 2B because of steric interactions between the ylide substituent and methylene unit of the [2.2.1] bicycle, and the high face selectivity in reaction of ylide conformer 2A was due to the camphor moiety effectively blocking attack from the si face. Based on this model, the camphor moiety was simply acting as a sterically large blocking group. But was it? If that was simply its role, similar levels of enantioselectivity should result from the diastereomer 5 where the carbonyl group is placed on the right of the [2.2.1] carbocycle (Fig. 1). ‡ In contrast, if the current model is too simplistic and the carbonyl group of the camphor skeleton does play a subtle role in contro...

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Section: Resultsmentioning

confidence: 99%

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications

Aggarwal

Charmant

Dudin

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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“…Different organic and inorganic oxidizing agents have been employed to this purpose, showing that high stereoselectivity is achieved only in the presence of a specific oxidant/substrate matching 34–44. One of the most frequently used oxidants in these reactions is m ‐chloroperbenzoic acid (MCPBA) which provides high levels of diastereoselectivity on a wide range of substrates 28–44.…”

Section: Introductionmentioning

confidence: 99%

“…In spite of the large number of examples so far reported in the literature, a detailed theoretical analysis at the molecular level of the factors determining the stereochemical outcome of the MCPBA sulfoxidation45 is still lacking. Some studies describe an active participation of the substrate hydroxy moieties in determining the direction of stereoinduction and the presence of H‐bonds between substrate and peracid has been invoked 28,29,34–36,38,41,42…”

Section: Introductionmentioning

confidence: 99%

Selective and Practical Oxidation of Sulfides to Diastereopure Sulfoxides: A Combined Experimental and Computational Investigation

et al. 2013

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chloromethane or methanol), following the Curtin-Hammett principle, the favoured path is the pro-R channel (M1!TS!M2) affording the (R c ,R s )-2a' product species in agreement with the observed diastereoselectivity. The M1-M1' and TS-TS' energy gaps are actually determined by the difference in the hydrogen bond network that features the two species even if the approaching orientation of the two molecules is governed by the interactions between the p systems of oxidant and substrate aromatic rings. The diastereomeric ratio computed on the basis of the energy difference between TS and TS' (0.7 kcal mol À1 ) is 63:37, which must be compared to the experimental value 9:1. When we consider free energy differences (2.4 kcal mol À1 in vacuum and 2.9 kcal mol À1 in solution) this theoretical ratio becomes 85:15 and 89:11, respectively, in excellent agreement with the experimental value 9:1.

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“…Note that the sulfur atom is chiral. 19 Based on the literature, 20,21 and based on our recent work, 18e, f as there is no neighboring hydroxyl group to assist, both of sulfur's electron pairs are available, and the results are logical. Two mentioned diastereoisomers can be separated by flash chromatography and characterized by spectroscopic methods (Scheme 2).…”

Section: Resultsmentioning

confidence: 99%

Poly(Ethylene) Glycol as a Green and Reusable Solvent in the Oxidation of Sulfides to Sulfoxides Using NaClO

Nemati

2010

Phosphorus, Sulfur, and Silicon and the Related Elements

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Self-induced diastereoselective oxidation of vinyl sulfoxides bearing a chiral hydroxy group as a way of preparation of optically active sulfinyl dienophiles and their use in the asymmetric Diels-Alder reactions to cyclopentadiene

Cited by 119 publications

References 7 publications

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications

Selective and Practical Oxidation of Sulfides to Diastereopure Sulfoxides: A Combined Experimental and Computational Investigation

Poly(Ethylene) Glycol as a Green and Reusable Solvent in the Oxidation of Sulfides to Sulfoxides Using NaClO

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