The anti-HIV agent (±)-calanolide A (1) has been synthesized in a five-step approach starting with phloroglucinol [→ 5→ 6→ 11→ 18→(±)-1], which includes Pechmann reaction, Friedel-Crafts acylation, chromenylation with 4, 4-dimethoxy-2-methylbutan-2-ol, cyclization, and Luche reduction. Cyclization of chromene 11 to chromanone 18 was achieved by employing either acetaldehyde diethyl acetal or paraldehyde in the presence of ...
[Zhang, Jintao; Kirchhoff, Eric W.; Zembower, David E.; Jimenez, Nancy; Sen, Prabir; Xu, Ze-Qi; Flavin, Michael T. Organic Process Research and Development, 2000 , vol. 4, # 6 p. 577 - 580]