21213-20-7Relevant academic research and scientific papers
Direct Allylic C(sp3)-H Thiolation with Disulfides via Visible Light Photoredox Catalysis
Hong, Soon Hyeok,Kang, Byungjoon,Kim, Jungwon
, p. 6013 - 6022 (2020/07/03)
In spite of the wide utility of allyl thioethers, the direct catalytic allylic C(sp3)-H thiolation remains elusive. Herein, we report the direct allylic C(sp3)-H thiolation mediated by visible light photoredox catalysis. The use of in situ-generated thiyl radical from disulfide as a hydrogen atom transfer (HAT) reagent and a coupling partner enabled selective cleavage of the allylic C(sp3)-H bond followed by C(sp3)-S bond formation. The undesired hydrothiolation, a prevalent reaction from facile thiyl radical addition to olefins, was prevented by the immediate deprotonation of thiol under basic conditions. A wide range of diaryl disulfides and olefins participated in the reaction, producing allyl thioethers with high efficiency. Mechanistic investigations revealed the participation of the photocatalyst as a redox mediator, which was crucial for the transformation of the allyl radical into the allyl cation and further ionic coupling process. Based on the proposed mechanism, a limitation in the synthesis of alkyl allyl sulfide was solved with a rationally designed more reducible unsymmetrical disulfide, which makes the desired catalytic cycle operative.
Aprotic Conjugate Addition of Allyllithium Reagents Bearing Polar Groups to Cyclic Enones. 2. 2-Alkyl-, 2,3-Dialkyl-, and 1,3-Dialkylallyl Systems
Haynes, Richard K.,Katsifis, Andrew G.,Vonwiller, Simone C.,Hambley, Trevor W.
, p. 5423 - 5433 (2007/10/02)
As an extension of the work carried out on the conjugate addition reactions of lithiated 3-alkylallylic sulfoxides, phosphine oxides, and phosphonates to cyclic enones, the effects of placing methyl groups at C2, at C2 and C3, and at C1 and C3 of the allyl system and of placing the allyl system within a five-membered ring are examined.From the lithiated 2-methallyl and (E)-2-methylbut-2-enyl ("tiglyl") sulfoxides, mixtures of diastereomeric (E)- and (Z)-vinilyc sulfoxides resulting from conjugate addition to cyclopentenone are obtained.The proportion of Z diastereomers formed increases with the reaction temperature.In contrast, lithiated (Z)-2-methylbut-2-enyl ("angelyl") sulfoxides and the tiglyl and angelyl phosphine oxides undergo highly diastereoselective conjugate addition to give (E)-vinylic products.Lithiated 1,3-dimethylbut-2-enyl sulfoxides undergo stereoconvergent reactions in that the starting sulfoxides, as mixtures of diastereomers, are converted into vinylic sulfoxides, which are obtained as single diastereomers.The individual diastereomers of tert-butyl cyclopentenyl sulfoxide upon lithiation undergo conjugate addition with cyclopentenone to give the same vinylic sulfoxide.A sulfenate ester also results from carbonyl addition.The structures of the diastereomers have been established by high-field (1)H NMR spectoscopy, by chemical correlation, and in two cases by X-ray crystallographic studies.The destabilizing influence of the methyl groups on the normal "trans-fused chair-chair"-like extended transition state causing access to "cis-fused boat-boat"-like, "cis-fused chair-chair"-like, and "trans-fused boat-chair"-like transition states involving planar lithiated reagents provides a rationale for the results.The temperature dependence of some of these reactions, and simple quenching experiments in which the individual lithiated diasteromers of the cyclopentenyl sulfoxide are converted into a single diasteromer, provide evidence for planar lithiated sulfoxides.
