Microwave Effects on Homogeneous Claisen Rearrangement and Heterogeneous Catalyzed Hydroalkoxylation

The use of microwaves as an alternative heating source has been growing for the past few decades. The utility as a rapid heating tool is known, but the overall impacts on chemistry and synthesis, still needs to be investigated. With growing reports of observed selective microwave effects, further understanding is required. This study investigates the use of additives both homogeneous and heterogeneous, and their impacts on synthetic microwave chemistry compared to traditional convective heating. The aryl-Clasien rearrangement is a well-studied unimolecular [3+3] sigmatropic rearrangement. Its use through out synthetic organic chemistry makes it a good candidate to study selective microwave heating. Here we investigated the addition of a chaperone molecule, in which a non-reactive but highly absorbing additive added the rearrangement under microwave irradiation but showed almost no improvement under conventional heating at comparable temperatures. Hydroalkoxylation is the reaction of an alcohol with either an alkene or alkyne to produce ethers. Recently, our group was studying the heterogeneous catalyzed aryl Claisen rearrangement of allyl phenyl ether, when the use of spinels as a catalyst afforded the 2-methylcoumaran as a byproduct. Under microwave conditions this byproduct was formed in higher yields when compared to that of the oil bath. It was then observed that the hydroalkoxylation of the 2-allylphenol produced the coumaran at a faster rate under microwave heating than conventional heating. In this study we investigated the utility of the spinel catalyzed hydroalkoxylation. Magnetite afforded the greatest conversion to the desired products in moderate to high yields.