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 gives a mixture of 6a-methyl-2,3,3a,6a-tetrahydrofuro[2,3-b]furan-2-one and 2-(2-methyl-3-furyl)acetic acid. Rhodium acetate catalyzed decomposition of 1-diazo-3-(3-benzofuranyl)-2-propanone and 1-diazo-3-(2-benzofuranyl)-2-propanone are also shown to undergo vinylogous Wolff rearrangement despite the fact that this chemistry is not observed with homologous benzofuranyl systems. α-Diazo ketones derived from benzothienyl propionic acids undergo the expected cyclization with 1-diazo-4-(3-benzothienyl)-2-butanone and 1-diazo-4-(2-benzothienyl)-2-butanone giving rise to 1,2,3,4-tetrahydrodibenzo[b,d]thiophen-3-one and 1,2,3,4-tetrahydrodibenzo[b,d]thiophen-2-one, respectively. While decomposition of 1-diazo-3-(3-benzothienyl)-2-propanone resulted in the formation of 2,3-dihydro-1H-benzo[b]cyclopenta[d]thiophen-2-one, the isomeric 1-diazo-3-(2-benzothienyl)-2-propanone gave a dimer which resulted from a [3 + 2] cycloaddition followed by a [1,3]-alkyl shift. Overall, the results from this study of intramolecular carbenoid insertion into five-membered heteroaromatic systems show that the resultant chemistry is dependent on the nature of the heteroatom, position of substitution, and the length of the aliphatic tether.