Synthesis of Isoflavones from 2′-Hydroxychalcones Using Poly[4-(diacetoxy)iodo]styrene or Related Hypervalent Iodine Reagent

Abstract

Isoflavones are synthesized in an one-pot reaction by treating the hypervalent iodine(III) reagent, [hydroxy(tosyloxy)iodo]benzene (HTIB, Koser’s reagent) with 2′-benzoyloxychalcones in MeOH. A combined use of (diacetoxyiodo)benzene (DIB)/p-toluenesulfonic acid (TsOH) is also effective for the same purpose. As an extension of these monomeric reagents, polymer-supported DIB {PSDIB, poly[4-(diacetoxy)iodo]styrene} with TsOH works also well. The merits of the latter are the ease of separation of iso­flavones from the reaction mixture, no liberation of PhI, and reuse of the reagent.

Key words

chalcones - isoflavones - protecting groups - hypervalent iodine - oxidative rearrangements

References

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10

The amount of NaOH was calculated as follows: The amount (1.5 equiv) needed for the ring closure of acetal 2h-Bz plus the amount (3.0 equiv) of HOAc formed by decomposition of DIB and that of TsOH (2.0 equiv).

11

Yields of one-pot synthesis of 3 from the corresponding 1-Bz using DIB/TsOH in CH₂Cl₂-MeOH are as follows: Isoflavones 3i (70%), 3j (77%), 3k (70%), and 3l (67%). In addition, the one-pot reactions of 1k-Bz with DIB/TsOH and PSDIB/TsOH proceeded without difficulty even in a mmol scale (a few grams), indicating the applicability of the present method for synthesis of a larger quantity as well. [16]

16

The experiments were done as a part of our ongoing synthetic studies on isoflavonoids. Details will be submitted elsewhere.