Abstract
Catalytic hydrogenation and chemical reduction of 2- and 3-substituted 1-indanones were carried out, and the steric configuration and the proportion of the products were determined. In the catalytic hydrogenation of 2-methyl-1-indanone [1], the cis-alcohol [5] was preferably formed irrespective of the catalysts, whereas in the case of metal hydride complex or Meerwein-Ponndorf reduction, [1] afforded trans-alcohol [6] as a main product. The hydrogenation of 2-phenyl-1-indanone [2] gave predominantly the cis-alcohol [8] with Raney-Ni or Pt catalyst, but over Pd catalyst the trans-alcohol [9] was formed more than the cis-alcohol. When [2] was reduced with lithium aluminum hydride, trans-alcohol [9] was produced as a main product, whereas in the case of sodium borohydride or lithium tri-t-butoxyaluminum hydride reduction, cis-alcohol [8] was obtained predominantly. In the case of chemical reduction or catalytic hydrogenation, 3-methyl-[3] and 3-phenyl-1-indanone [4] gave the cis-alcohol in high yield.
On the basis of the above results, the stereochemistry concerning the reduction of 1-inda-nones was discussed. In the catalytic hydrogenation, it was considered that the reaction proceeds via a π-benzylic type half-hydrogenated state and that the predominant production of the trans-alcohol in the hydrogenation of [2] catalyzed by Pd is attributed to the bulkiness of the phenyl group.
