Abstract
The total synthesis of decarboxyaltenusin (5’-methoxy-6-methyl-[1,1’-biphenyl]-3,3’,4-triol), a toxin produced by various mold fungi, has been achieved in seven steps in a yield of 31% starting from 4-methylcatechol and 1-bromo-3,5-dimethoxybenzene, where the longest linear sequence consists of five steps. The key reaction was a palladium-catalyzed Suzuki coupling of an aromatic boronate with a brominated resorcin derivative.
Highlights
To continue our efforts in the total synthesis of mycotoxins [8,9,10,11,12,13,14,15,16,17,18] and to provide larger amounts of the polyketide 1 sufficient for thorough biological investigations, we considered it useful to supply a more straightforward synthesis of this compound, for which we here propose the obvious name decarboxyaltenusin
The synthesis of the benzyl-protected boronate was here achieved with a modified strategy including bromination [21] of 4-methylcatechol (2) to the known bromide 4 [26] and subsequent benzyl protection to the bis(benzyl ether) 5b using standard conditions (Scheme 2) [27]
The preparation of boronate 6b applying the conditions used for the silylated substrate 6a led to a mediocre 44% yield, but Scheme 2: Synthesis of arylboronates 6
Summary
Scheme 3: Synthesis of aryl bromides 9. The boronate moiety 6a was prepared starting with 4-methylcatechol (2), which was initially protected with tert-butyldimethylsilyl chloride in the presence of 4-(dimethylamino)pyridine (DMAP) and imidazole (Scheme 2) according to a published procedure [20]. The electrophilic compound suitable for the projected cross coupling was obtained by mono-demethylation of commercially available 1-bromo-3,5-dimethoxybenzene (7) with boron tribromide (Scheme 3).
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