Lewis acid (BF3∗OEt2) mediated allylation of methoxy-p-benzoquinone [5] with trans-cin-namyltrimethyltin at low temperature and successive mild oxidation gives -4-methoxydal-bergione [3] an antibiotic, in high regioselectivity (77%) and good yield. The reaction system posesses the possibility of forming six regioisomers, and the present synthetic method is the first successful example for the synthesis of [3] from the corresponding quinone Other Lewis acids (SnCl4, A1C18) were ineffective for the reaction both in regioselectivity and in yield. The amount of BF3OEt2slightly affected the regioselectivity and the best selectivity was obtained when three equivalent of BFaOEt2was used. The selective coordination of BFa.OEt2to MeO group of the quinone is proposed for the explanation of the high selectivity. This method is suggested to be promising for the synthesis of important intermediates of versatile bioactive quinones. © 1981, The Chemical Society of Japan. All rights reserved.