Multigram‐scale concise synthesis of the ring A of bilirubin and related compounds

A multigram‐scale concise synthesis of the ring A of bilirubin, a pyrrolinone bearing a vinyl group, was achieved, from cheap and available cis‐2‐butene‐1,4‐diol in 40% overall yield in four steps. The key step involved the intramolecular cyclization of aldehyde with amide and the rearrangement of the ethylidene group. A multigram‐scale concise synthesis of the ring A of bilirubin was achieved from cis‐2‐butene‐1,4‐diol in four steps. The key step involved the intramolecular cyclyzation of aldehyde with amide and the rearrangement of the ethylidene group.