A new method is reported for the conversion of azidoacids into lactams, via thioester formation and in situ azide reduction and cyclisation under high-dilution conditions; since the quantitative conversion of macrolactams to macrolactones has been shown to be feasible, this results in an indirect, alternative macrolactonisation procedure.
Disclosed is a composition comprising (A) at least one compound selected from the group consisting of an ether compound having two or more ether groups, a trivalent phosphorus compound, and a ketone compound, (B) a boron trihalide, and (C) an episulfide compound.