Synthesis, Structure, and Unusual Reactivity of a Stable 3‑(Oxazolidin-2-ylidene)thiophen-2-one

Treatment
of 2- and 3-thienyloxazolines with butyllithium and bis­(trimethylsilyl)
peroxide results in ring hydroxylation to give products that exist
mainly as the oxazolidinylidenethiophenones. The 3-oxazolidinylidenethiophen-2-one
is a rare example of a stable heterocyclic o-quinone
methide analogue that shows a varied pattern of reactivity, including
both C- and O-alkylation, Michael
addition via C-5 to an acetylenic ester, tetrachlorobenzannulation
across positions 4 and 5, and formation of a hexacyclic fused-ring
product with N-phenyltriazolinedione. Crystal structures
of the products are dominated by inter- and intramolecular NH to CO
hydrogen bonding.