In the presence of zinc dust (1.5−2.0 equiv) and LiCl (1.5−2.0 equiv), various benzylic chlorides bearing functional groups (iodide, cyanide, ester, ketone) are smoothly converted at 25 °C to the corresponding zinc reagents without homo-coupling (<5%). The utility of these benzylic zinc reagents is demonstrated by a short synthesis of papaverine.
- Metzger, Albrecht; Schade, Matthias A.; Knochel, Paul. LiCl-Mediated Preparation of Highly Functionalized Benzylic Zinc Chlorides. Org. Lett., 2008, 10, 1107-1110.
Treatment of (tmp)MgClLiCl (1) with ZnCl2 (0.5 equiv, 25 °C, 15 h) provides (tmp)2Zn2 MgCl22 LiCl (2). The resulting solution of the complex base has a high activity for the zincation of sensitive heterocycles such as 2-phenyl-1,3,4-oxadiazole (3) and N-tosyl-1,2,4-triazole (4).
- Wunderlich, Stefan H.; Knochel, Paul. (tmp)2Zn2 MgCl22 LiCl: A Chemoselective Base for the Directed Zincation of Sensitive Arenes and Heteroarenes. Angew. Chem. Int Ed., 2007, 46, 7685-7688.
A wide range of polyfunctional aryl and heteroaryl zinc reagents were efficiently prepared in THF via direct zincation using (tmp)2Zn·2MgCl2·2LiCl and microwave irradiation. Ester and cyano functions as well as ketones are compatible with the high temperatures of the zincation. The resulting bis-organo zinc species undergo a number of subsequent reactions leading to highly functionalized aromatics and heteroaromatics in good to excellent yields.
- Wunderlich, Stefan H.; Knochel, Paul. High Temperature Metalation of Functionalized Aromatics and Heteroaromatics using (tmp)2Zn·2MgCl2·2LiCl and Microwave Irradiation. Org. Lett., 2008, 10, 4705–4707.
A wide range of polyfunctional aryl and heteroaryl zinc reagents were efficiently prepared in THF by using (TMP)2Mg2 LiCl (TMP=2,2,6,6-tetramethylpiperamidyl) in the presence of ZnCl2.
- Dong, Zhibing; Clososki, Giuliano C.; Wunderlich, Stefan H.; Unsinn, Andreas; Li, Jinshan; Knochel, Paul. Direct Zincation of Functionalized Aromatics and Heterocycles by Using a Magnesium Base in the Presence of ZnCl2. Chem. Eur. J., 2008, 15, 457-468.
Benzylic zinc chlorides bearing various functional groups are smoothly prepared by the direct insertion of magnesium into benzylic chlorides in the presence of LiCl and ZnCl2.
Metzger, Albrecht; Piller, Fabian; Knochel, Paul Polyfunctional benzylic zinc chlorides by the direct insertion of magnesium into benzylic chlorides in the presence of LiCl and ZnCl2. ChemComm, 2008, 5824 - 5826.