S–S Bond cleavage of polymerization resistant 1,2-dithiolanes by acetylides: intrinsic reactivity of enzyme-bound lipoic acid toward stable, localized carbanions

The S–S bond of polymerization-resistant 1,2-dithiolanes 2 was cleaved cleanly by acetylides 4, giving the corresponding ring-opened products 5 in aprotic THF (quenched as silylsulfide 6) and their re-cyclized products 6,7-dihydro-1,4-dithiepins 3 in protic ButOH in excellent yields. The reactivity of 2 is discussed in relation to the reductive acylation of the enzyme-bound lipoic acid (Lip-E2).