The relative rates of reaction of (ethoxycarbonyl)carbene (1), formed by the thermal decomposition of ethyl diazoacetate (2), with toluene, anisole, phenanthrene, pyridine, quinoline, acridine, furan, benzofuran, dibenzofuran, thiophene, benzothiophene, dibenzothiophene, pyrrole, indole, carbazole, fluorene, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2,4-trimethoxybenzene, 1-methoxynaphthalene, 2-methoxynaphthalene, 2,6-dimethoxynaphthalene, and 2,7-dimethoxynaphthalene versus naphthalene at 150/degrees/C were measured. The relative rate data for the four series toluene, naphthalene, and phenanthrene, the furans, the thiophenes, and the pyrroles are consistent with direct addition of 1 to the aromatic ring systems. Significantly, the more nucleophilic ring systems show a selectivity of up to a factor of about 100 relative to the simple benzene derivative toluene. The pyridine, quinoline, acridine series appears to react with 1 by an ylide mechanism, and in these cases, the selectivities are even larger, up to about 150 relative to toluene. Thus, unlike the reaction of 1 with a series of substituted benzenes, where the selectivity is fairly modest, the heteroaromatic systems studied here show selectivities that are quite large. Methoxy substitution on benzene and naphthalene gives rise to only limited increases in selectivity with one or two groups on the ring system; however, 1,2,4-trimethoxybenzene shows a significantly increased selectivity. Kinetic measurements were consistent with carbene formation beingmore » the rate-determining step in these reactions. 29 references, 3 tables.« less