Pyridine-catalysed chromenylation of mono-chelated meta-dihydric phenols with mono-, sesqui- and di-terpene aldehydes: synthesis of rubranine and flemingins A-, B- and C-methyl ethers
- 1 January 1971
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society C: Organic
- p. 804-810
- https://doi.org/10.1039/j39710000804
Abstract
meta-Dihydric phenols in which one hydroxy-group is engaged in chelation, undergo pyridine-catalysed reaction with citral to give chromens, further cyclisation to ‘citrylidene’ types being inhibited. The reaction is deployed to synthesise the three natural flemingins, A (VIII), B (IX) and C (X) as their methyl ethers. Pinocembrin (XXIV) condenses with citral, with cleavage of the chromone accompanying the initial chromenylation. By use of the newly formed hydroxy-group, cyclisation continues and the product is the ‘citrylidene’-type (XXVI) having a cinnamoyl substituent. This has proved to be identical with the new natural product rubranine, recently isolated from rosewood. Chromenylation of 2-methyl-5,7-dihydroxychromone with citral has been studied. Farnesal and phytal condense with mono-chelated meta-dihydric phenols in the same way as citral, giving long-chain chromens.Keywords
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