Intramolecular Carbenoid Insertions: Reactions of α-Diazo Ketones Derived from Furanyl-, Thienyl-, (Benzofuranyl)-, and (Benzothienyl)acetic Acids with Rhodium(II) Acetate

α-Diazo ketones tethered to furan, benzofuran, thiophene, and benzothiophene by a single methylene spacer have been shown to undergo atypical, rhodium(II) acetate catalyzed chemistry. For example, while treatment of 1-diazo-3-(3-furanyl)-2-propanone with Rh2(OAc)4 resulted in the expected 2-(4-oxo-2-cyclopentenylidene)acetaldehyde, isomeric 1-diazo-3-(2-furanyl)-2-propanone undergoes a vinylogous Wolff rearrangement and in the presence of water …