Concise Formal Synthesis of (S)-Gregatin B

S)-3- Acetyl-5-[(1E,3E)-1,3-hexadienyl]-4-hydroxy-5-methyl-2(5H)furanone, known precursor for the synthesis of (S)-gregatin B, was synthesized in a fewer steps and higher overall yield starting from (R)-lactic acid.(S)-Gregatins A, B 1 and (R)-aspertetronins A, B 2 were isolated from Cephalosporium gregatum and Aspergillus panamensis, respectively, as antimicrobial metabolites and phytotoxic substances. 3They are regarded as the derivatives of 3-acyltetronic acid which possesses the same side chain at C5, although the chirality is different (Figure 1).On the synthetic research of these compounds, only one report for the synthesis of (S)-gregatin B appeared in 1984, 4 but the multi-steps were required and the total yield was relatively low.