Synthesis of Dihydrobenzo[h]coumarins and Their 4‐Methyl Analogs

Abstract

Dihydrobenzo[h]coumarins (5a–7a) and their 4‐methyl analogs (5b–7b) were synthesized from 1‐naphthol via two different synthetic routes. One pathway is the direct condensation of 5,8‐dihydro‐1‐naphthol (9) with malic acid or ethyl acetoacetate, affording 7,10‐dihydrobenzo[h]coumarins 7a and 7b, respectively. The other is through the oxidation of 7,8,9,10‐tetrahydrobenzo[h] coumarins (15a–b), followed by the reduction of the carbonyl group and dehydration of hydroxyl group, giving 7,8-dihydrobenzo[h]coumarins (5a, b) and 9,10-dihydrobenzo[h]coumarins (6a, b). The regio selectivities for the oxidation reactions of 15a, b were rationalized on the basis of quantum chemical calculations and further confirmed by the X‐ray crystallographic analysis of the derivatives of oxidation products.

Keywords:

• Dihydrobenzo[h]coumarins
• 4‐methyl‐dihydrobenzo[h]coumarins
• 7,8,9,10‐tetrahydrobenzo[h]coumarins
• oxidation
• regioselectivity

Acknowledgment

This research was supported by grants from the National Natural Science Foundation of China (No. 20272010 and 30200348) awarded to P. Xia and Y. Chen, respectively, and the research grant (No. 2000246069) for Ph.D. program from National Education Administration of China awarded to P. Xia.