Synthesis of PNA hydrocarbons

The synthesis of PNA hydrocarbons usually includes ring construction, aromatization, removal of oxygen or other heteroatoms and in some cases specific placement of alkyl or aryl groups. These topics are of current interest in our laboratory. We have examined the regioselectivity of the Haworth sequence (Scheme I, Table I) and chromic acid oxidation at the benzylic position (Scheme II) as routes to 1-tetralones which in turn can become parent aromatic hydrocarbons or alkyl substituted ones (Scheme III). Simultaneous aromatization and deoxygenation can be accomplished in a single step by heating 1-tetralones in the presence of alkali (Scheme IV, Table VI). The deoxidative coupling of substituted acetophenones to stilbene types using active titanium species as coupling agents and subsequent photocyclization (Scheme IX) has provided a convenient route to polymethylphenathrenes. The maleic anhydride (Diels-Alder) route to ring construction (Scheme X) can be improved through use of Pd/C or PbO/sub 2/ as a reagent for bis-decarboxylation of vicinal anhydrides.