On the deprotonation of η6-1,3-dimethoxybenzene-Cr(CO)3 derivatives: Influence of the reaction conditions on the regioselectivity

✍ Scribed by Hans-Günther Schmalz; Thorsten Volk; Dirk Bernicke; Siegfried Huneck

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 865 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)00620-0

✦ Synopsis

The regioselectivity of deprotonation / alkylation reactions of q6 1,3_dimethoxybenzene_Cr(CO) 3 (5), -q6.1,3_dimethoxy.5_methylbenzene_Cr(CO) 3 (6) and 2-substituted derivatives of these compounds was investigated. It is shown that the regioselectivity highly depends on the reaction conditions. For instance, deprotonation of q6_ 1,3-dimethoxy-2-(trimethylsilyl)benzene-Cr(CO)3 (10) with n-BuLi followed by silylation or methylation affords 4-substituted products while the use of LiTMP at -78 °C cleanly gives rise to 5-substituted products. The regioselective alkylation of complexes of type 6 at the 5-methyl group is easily achieved. The usefulness of the latter possibility is demonstrated in a synthesis of olivetol dimethyl ether (33).