Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193 (Japan), Fax: (+81) 58-293-2614; JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan).
Chemistry. 2013 Sep 23;19(39):13112-9. doi: 10.1002/chem.201301573. Epub 2013 Aug 14.
The sequential addition of aromatic Grignard reagents to O-alkyl thioformates proceeded to completion within 30 s to give aryl benzylic sulfanes in good yields. This reaction may begin with the nucleophilic attack of the Grignard reagent onto the carbon atom of the O-alkyl thioformates, followed by the elimination of ROMgBr to generate aromatic thioaldehydes, which then react with a second molecule of the Grignard reagent at the sulfur atom to form arylsulfanyl benzylic Grignard reagents. To confirm the generation of aromatic thioaldehydes, the reaction between O-alkyl thioformates and phenyl Grignard reagent was carried out in the presence of cyclopentadiene. As a result, hetero-Diels-Alder adducts of the thioaldehyde and the diene were formed. The treatment of a mixture of the thioformate and phenyl Grignard reagent with iodine gave 1,2-bis(phenylsulfanyl)-1,2-diphenyl ethane as a product, which indicated the formation of arylsulfanyl benzylic Grignard reagents in the reaction mixture. When electrophiles were added to the Grignard reagents that were generated in situ, four-component coupling products, that is, O-alkyl thioformates, two molecules of Grignard reagents, and electrophiles, were obtained in moderate-to-good yields. The use of silyl chloride or allylic bromides gave the adducts within 5 min, whereas the reaction with benzylic halides required more than 30 min. The addition to carbonyl compounds was complete within 1 min and the use of lithium bromide as an additive enhanced the yields of the four-component coupling products. Finally, oxiranes and imines also participated in the coupling reaction.
芳基格氏试剂与 O-烷基硫代甲酸盐的顺序加成在 30s 内完成，以高产率得到芳基苄基硫醚。该反应可能从格氏试剂对 O-烷基硫代甲酸盐的碳原子的亲核攻击开始，随后消除 ROMgBr 生成芳基硫代醛，然后与第二个格氏试剂分子在硫原子上反应，形成芳基硫基苄基格氏试剂。为了确认芳基硫代醛的生成，在环戊二烯的存在下进行 O-烷基硫代甲酸盐与苯基格氏试剂的反应。结果，形成了硫代醛和二烯的杂 Diels-Alder 加合物。将硫代甲酸盐和苯基格氏试剂的混合物与碘处理得到 1,2-双（苯基硫基）-1,2-二苯基乙烷作为产物，这表明在反应混合物中形成了芳基硫基苄基格氏试剂。当向原位生成的格氏试剂中加入亲电试剂时，得到了四组分偶联产物，即 O-烷基硫代甲酸盐、两个格氏试剂分子和亲电试剂，产率中等至良好。使用硅氯化物或烯丙基溴化物可在 5 分钟内得到加合物，而与苄基卤化物的反应则需要 30 分钟以上。与羰基化合物的加成在 1 分钟内完成，并且使用溴化锂作为添加剂可以提高四组分偶联产物的产率。最后，环氧化物和亚胺也参与了偶联反应。
