Formylation of Methylnaphthalene Compounds with CO in HF-BF3 Medium.

Abstract

The formylation of naphthalene compounds, including 2-methylnaphthalene (1a), 1-methylnaphthalene (1b), 1, 2, 3, 4-tetrahydro-2-methylnaphthalene (1c), and 5, 6, 7, 8-tetrahydro-2-methylnaphthalene (1d), with pressurized CO was investigated in HF-BF3 medium at ambient temperature. With pressurized BF3 (6atm) and CO (50atm) at 25°C, 1a was formylated readily to yield a mixture of five isomers of aldehydes in total yield of 72%, in which 6-formyl-2-methylnaphthalene was produced as the major regioisomer in selectivity of 33%. In contrast, 1b produced predominantly 4-formyl-1-methylnaphthalene in yield of 60% together with a small amount (2.8%) of 2-formylated product. In the cases of tetralin ompounds, 1c produced ca. 1:1 of 6- and 7-formyl-1, 2, 3, 4-tetrahydro-2-methylnaphthalenes, in total yield of 98%. On the other hand, 1d produced only one product, 3-formyl-5, 6, 7, 8-tetrahydro-2-methylnaphthalene, in yield of 64%. In the formylation of 1a, the effects of the reaction variables, such as the pressure of BF3 and reaction temperature, on the yield and positional selectivities were examined, and also compared with the results in other acid media.