A Short and Efficient TotalSynthesis of the Naturally Occurring Coumarins Siderin, Kotanin,Isokotanin A and Desertorin C

Abstract

Starting from methyl 2-hydroxy-4-methoxy-6-methylbenzoate (6) and its regioisomeric dehydrodimers 7-9,readily available by an oxidative coupling reaction of 6, the naturally occurring coumarins siderin(1), kotanin (2),isokotanin A (3) and desertorin C (4) were synthesized in a novel and highlyefficient three-step transformation. In the case of kotanin (2) both atropisomers were prepared fromthe pure atropisomers of 7.

Key words

atropisomerism - biaryls - oxidative phenoliccoupling - natural coumarins

References

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10

The total syntheses of the three biarylcoumarins 2-4 require ca.25 steps according to the literature.

17

This was demonstrated for the 6,8′-bisaminochromenone 15, which was converted to desertorin C(4) in a single step. Hence, the hydrolyticmixture was dehydrated chemically with dimethyl carbonate afterno starting material could be detected (TLC). Acetyl chloride wasadded to generate additional HCl. The yield (34%) is comparableto the overall yield of the two-step procedure (36%).

18

The low yield in the case of M-(-)-2 ismainly due to a nonoptimized reaction time for acidic hydrolysis.

19

The isomers of kotanin(2)were erroneously mismatched in a previous publication. [11a]

21

Crystallographic data (excluding structurefactors) for the structures reported in this paper have been depositedwith the Cambridge Crystallographic Data Centre as supplementary publicationno. CCDC-215646. Copies of the data can be obtained free of chargeat www.ccdc.cam.ac.uk/conts/retrieving.html [orfrom the Cambridge Crystallographic Data Centre, 12 Union Road,Cambridge CB2 1EZ, UK; Fax: int. code+44-1223/336-033;e-mail: [e-mail]].