ON THE DEPROTONATION OF ETA(6)-1,3-DIMETHOXYBENZENE-CR(CO)(3) DERIVATIVES - INFLUENCE OF THE REACTION CONDITIONS ON THE REGIOSELECTIVITY

The regioselectivity of deprotonation / alkylation reactions of eta(6) -1,3-dimethoxybenzene-Cr(CO)(3) (5), eta(6)-1,3-dimethoxy-5-methylbenz ene-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 -1,3-dimethox y-2-(trimethylsilyl)benzene-Cr(CO)(3) (10) with n-BuLi followed by sil ylation or methylation affords 4-substituted products while the use of L1TMP at -78 degrees C cleanly gives rise to 5-substituted products. The regioselective alkylation of complexes of type 6 at the 5-methyl g roup is easily achieved. The usefulness of the latter possibility is d emonstrated in a synthesis of olivetol dimethyl ether (33). (C) 1997 E lsevier Science Ltd.