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■ Selective Introduction of Four Contiguous Stereocenters on the B-Ring of 4-Hydroxyzinowol

Masafumi Iwatsu, Daisuke Urabe, Hidenori Todoroki, Kengo Masuda, and Masayuki Inoue*

*Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract

4-Hydoxyzinowol is a bioactive polyoxygenated dihydro-β-agarofuran sesquiterpenoid. Here we describe construction of four contiguous cis-oriented stereocenters on the B-ring of 4-hydroxyzinowol. Introduction of a C7-isopropenyl group by the 1,4-addition of isopropenyl magnesium bromide was effectively assisted by methyl aluminum bis(2,6-di-tert-butyl-4-methylphenoxide). Taking advantage of the presence of the C7-substituent, three hydroxy groups were installed in a stereoselective fashion at the C6, 8 and 9 positions. In this study, we employed a new reagent combination of Sc(OTf)3 and Zn(OTf)2 for the hydrolysis of the cyclic acetal on the rigid oxabicyclo[3.2.1]octane structure.