The first synthesis of 7-(hydroxymethyl)thiepane-3,4,5-triols from d-(−)-quinic acid

Seven thiepanes, the seven-membered-ring thiosugars, were first synthesized in 11-12 steps starting from d-(−)-quinic acid. Each thiepane is unique for its flexible conformation with a hydroxymethyl group at its C7 position. The key step was the deprotection of ether groups in compounds 7, 8, and 18-21 by 1.0 M BCl3 of CH2Cl2 solution at −78 °C to lead to the corresponding thiepanes. These target molecules all exhibited the twisted chair conformation that fully agreed with our previous report.