Hydroalumination cross coupling chemistry using enynols & uncatalyzed Diels-Alder reactions of siloxacyclopentenes prepared from hydrosilylation of enynols

For some time the Welker research group has been attaching metals to the third carbon of a diene 0.1 used in Diels-Alder chemistry. The basic structure of a diene is illustrated below in Figure 0.1 (1).*;The purpose behind this metal diene is three fold. First, a large metal helps keep the diene in the reactive s-cis confirmation, a requirement for a Diels-Alder reaction. Second, the presence of a bulky metal can also help control the diene and dienophile from generating the endo Diels-Alder product. The endo product is traditionally the most favored product due to the fact it results from pi bond overlap between the diene and dienophile 0.2. The endo product also results in a syn addition cycloadduct 0.3. By blocking the endo approach using a bulky metal a synthetically viable pathway to the exo product is achieved 0.4, resulting in the anti addition product 0.5 (see Figure 0.2). The traditional diene 0.2 allows the dienophile access to its pi orbitals, resulting in an endo product 0.3. However the diene 0.4 that has a metal attached (if the metal is bulky enough) can block the dienophile resulting in the exo product 0.5. Third, by placing a metal on the diene, one of the terminal carbons (1 or 4) becomes more electronegative than the other thereby helping to direct regiochemistry.*;Initially in the Welker group, this was done by using cobalt on the diene (1). While this method worked well, it only worked in stoichiometric amounts of cobalt and could not be adapted to a catalytic system. This posed a problem due to the high cost of cobalt. To this end a new strategy was designed, in which a diene would have a main group metal on the third carbon. Specifically, a series of dienes, will be made using aluminum and silicon, the 3 rd and 2nd most common elements found in the earth's crust, respectively (2). While aluminum and silicon have been used in organic chemistry for some time their ability to assist cycloaddition chemistry is somewhat limited. To expand the synthetic usefulness of aluminum and silicon dienes a transmetallation reaction will also need to be developed to replace the aluminum or silicon with a synthetically versatile transition metal such as Pd.;*Please refer to dissertation for diagrams.