Synthetic Methods. Part 39. Reactions and Rearrangements in 2-Oxa(3.2. 0)bicycloheptanones

The furan-fused chlorocyclobutanone 6 undergoes reaction with O, N, S, C nucleophiles at a much slower rate than its pyran homolog, which is attributed to a reluctance to enolization. Instead of substitution products, rearranged products were formed. For instance, 7-membered ring lactones 8 and 9 were derived via vinyl ketenes, while 5-membered ring lactones 12, 19, and 20 resulted from opening of the cyclobutanone and/or of the tetrahydrofuran ring. Phenylthiolate behaved exceptionally as a nucleophile, leading, presumably via electron transfer, to ipso substitution and then to a naphthofuran.