19 π(アレーン)トリカルボニルクロム錯体の位置選択的リチウム化反応及びRabelomycinの合成研究

概要

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(3-Methoxybenzyl alcohol)tricarbonyl chromium complex 8 and (2-substituted-7-methoxy-1-tetralol)chromium complexes 9 are selectively lithiated at the 4-position and 6-position, respectively, by the treatment with n-BuLi/TMEDA. The regioselectivity of this lithiation increase with increasing bulkiness of the butyllithium reagent employed. Since the direct lithiation of the corresponding chromium free arenes, 1, 2 and 3 proceeds at the 2- and 8-position, respectively, this different regioselectivity of the lithiation is useful for the synthesis of substituted arene compounds. The difference is explained by the relative configuration of the tricarbonyl chromium group in the π(arene)Cr(CO)_3 complexes, and the electric repulsion effect. On the other hand, the chromium complexes of arenes without free hydroxyl group, such as benzylmethyl ether or ethyleneacetals of 3-oxygenated benzaldehydes, are lithiated at the 2-position preferentially, in contrast to the above results with benzyl alcohol derivatives. The synthetic studies on Rabelomycin 21 are in progress by using this regioselective lithiation of π(arene)tricarbonyl chromium complexes.
天然有機化合物討論会の論文
1982-09-10