A Stereoselective Switch Enantiodivergent Approach to the Synthesis of Isoflavanones

A Stereoselective Switch Enantiodivergent Approach to the Synthesis of Isoflavanones 

Two examples of these types of isoflavanones are the naturally occurring sativanone la and 3-0-methylviolanone lb (Fig. 5.2). Sativanone la was first isolated in 1973 by Donnelly from the heart wood of Dalbergia stevensonii [6] and has been shown to display activity against human cancer cell lines as well as antibacterial activity [7, 8]. There has been one reported racemic synthesis of sativanone la via a 4 step synthesis involving intramolecular cyclisation to form the B ring of the isoflavanone [9]. 3-0-Methylviolanone, first isolated in 1975 from Dalbergia 

1 Common substitution patterns in naturally occurring isoflavanones 

Unsurprisingly due to their potential as medicinal agents there have been many reported synthetic routes to isoflavanones including the reduction of corresponding isoflavones, [12] benzylic oxidation of isoflavans, [13] gold-catalysed annulations, [14] addition of C-O bonds to arynes [15] and palladium catalysed a-arylation [16]. Despite the multitude of syntheses reported over the past 70 years few routes have been shown to be truly modular with respect to substituents on the isoflavanone skeleton and only one route was asymmetric, relying on the use of chiral auxiliaries [17]. 

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