The Birch reduction of 2, 7-dimethoxy-3-isopropylnaphthalene (IIb), which itself was made from IIa in five steps, followed by acid hydrolysis yielded the tetralone IIIa and the latter was carboxymethylated to IIIb by reaction with dimethyl carbonate and sodium hydride. Michael condensation of IIIb with methyl vinyl ketone yielded the unsaturated ketone IV. The tricyclic ketone IV on methylation followed by thioketalisation gave the thioketal IXa and the latter ...
