Thiophene systems. 11. The synthesis of novel thieno[4,3,2-de] tricyclic ring systems

The synthesis of thieno[4,3,2-de] tricyclic compounds is described. The N-1 alkylation of I produced the alkanoic ester precursors. After hydrolysis, the corresponding carboxylic acids were cyclized to the title compounds II. This cyclization step was accomplished with 1:10 phosphorus pentoxide-methanesulfonic acid. The ketones II were further modified to introduce additional functionality onto this novel tricyclic ring system.