Michael addition of methylvinyl ketone to 2-methylcycloheptane-1, 3-dione (II) obtained by methylation of cycloheptane-1, 3-dione furnishes 2-methyl-2 (3′-oxobutyl) cycloheptane-1, 3-dione (III) which is cyclized and dehydrated in a single step to afford the title compound (Ic) in the presence of a mixture of pyrrolidine and acetic acid. A by-product isolated in this cyclization is the bridged ketol VII. Treatment of III with p-toluenesulphonic acid gives ...
