(+)-Cystothiazole G: isolation and structural elucidation

Palladium-catalyzed cyclization-methoxycarbonylation of (2R,3S)-3-methylpent-4-yne-1,2-diol (6) derived from (2R,3S)-epoxybutanoate 5 followed by methylation gave the tetrahydro-2-furylidene acetate (−)-7, which was converted to the left-half aldehyde (+)-3. A Wittig reaction between (+)-3 and the phosphoranylide derived from the bithiazole-type phosphonium iodide 4 using lithium bis(trimethylsilyl)amide afforded the (+)-cystothiazole G (2), whose spectral data were identical with those of the natural product (+)-2. Thus, the stereochemistry of cystothiazole G (2) was proved to be (4R,5S,6(E)).