Abstract
The reduction of 3, 4-dihydroisocoumarins (1, 3, 6, 11a, 11b, and 12b) having a hydroxyl group or acetoxyl group at the C(8)-position adjacent to the lactone carbonyl group with lithium aluminum hydride gave novel products, 1, 8-dihydroxyisochromans (10a, 13, and 16a), in addition to 8-hydroxyisochromans (2, 8, and 14) and 2-(3-hydroxy-2-hydroxymethylphenyl)-ethanols (4, 9, and 15). The isochromans and 2-(2-hydroxymethylphenyl)-ethanols are known reduction products of 3, 4-dihydroisocoumarins lacking a C(8)-hydroxyl group. In addition, 13 was obtained selectively in 50% yield by reduction of the magnesium chelate of 11a with lithium aluminum hydride. Similarly, 8-hydroxy-3-phenylisocoumarin (23a) and 8-acetoxy-3-phenylisocoumarin (23b) both gave 2-formyl-3-hydroxybenzyl phenyl ketone (24). Based on these results, a mechanism for the reduction of 8-hydroxy-3, 4-dihydroisocoumarins is proposed, as shown in Chart 3.
