cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin

• Main Authors: Dimpee Gogoi, Runjun Devi, Pallab Pahari, Bipul Sarma, Sajal Kumar Das
• Format: Article
• Language: English
• Published: Beilstein-Institut 2016-12-01
• Series: Beilstein Journal of Organic Chemistry
• Subjects: brazilin; chroman; epoxy-arene cyclization; natural-product-like molecules; tetralin
• Online Access: https://doi.org/10.3762/bjoc.12.280

We have synthesized a series of cis-6a,7,8,12b-tetrahydro-6H-naphtho[2,1-c]chromen-6a-ols as B-ring-modified analogues of (±)-brazilin. A completely regio- and cis-diastereoselective intramolecular Friedel–Crafts epoxy–arene cyclization of 1-tetralone-derived glycidyl ethers catalyzed by Brønsted acids was used as the key step. Our worries concerning the formation of cis–trans product mixtures and their probable conversion to naphthopyran derivatives via dehydration of the tertiary hydroxy group were laid to rest. Additionally, the angular hydroxy group of one of the synthesized products has been reductively removed by a diastereoselective method which should be useful in future for preparing libraries of chroman-fused tetralins with trans-stereochemistry at the ring junction.