Halenaquinol dimethyl ether

Halenaquinol 2 was methylated in refluxing acetone with iodomethane in the presence of potassium carbonate in the dark yielding dimethyl ether (+)-17 as yellow needles (Scheme 1) mp 235 °C [a]23 )+150.1° (CH2CI2). To differentiate the two carbonyl groups at the 3- and 6-positions, halenaquinol dimethyl ether (+)-17 was selectively reduced with NaBH4 in the presence of CeCl3-7H20, which... 

Figure 2. CD spectrum of halenaquinol dimethyl ether (12b5)-(+)-17 derived from the natural sample of halenaquinol solvent, EtOH.

The naphthalene-diene compounds (-)-22 and (+)-23 were also derived directly from halenaquinol dimethyl ether (+)-17 by the reduction and subsequent terr-butyldimethylsilylation (Scheme 3). Diketone (-i-)-17 was reduced and then treated with hydrochloric acid, as in the case of ketone (+)-19 of Scheme 2, giving rranj-methoxy alcohol (-)-24 and cj j-methoxy alcohol (-)-25, respectively. Each alcohol was then converted to its /ert-butyldimethylsilyl ether, which was identical with the authentic sample derived from compound (+)-19. 

In the case of the total synthesis of halenaquinol (12b5)-(+)-2 and halenaquinone (12b5)-(+)-l, we started from the Wieland-Miescher ketone (8a/ )-(-)-33, as discussed above. Therefore, it is evident that the synthetic sample of halenaquinol dimethyl ether (+)-17 has the (12b5) absolute configuration. 19 if the theoretical determination of the absolute stereochemistry of the halenaquinol family is correct, the chiroptical data of [ ]d and CD spectra of the synthetic sample should be identical with those of the authentic sample of (+)-17 derived from... 

As discussed above, the absolute stereochemistry of halenaquinone (+)-l and halenaquinol (+)-2 has been theoretically determined by the calculation of the CD spectra of naphthalene-diene derivatives by means of the tt-electron SCF-CI-DV MO method. 18 To apply the same method to these xestoquinone compounds, xesto-quinol dimethyl ether (+)-74 was converted to naphthalene-diene derivative 75 by reduction with sodium borohydride in the presence of cerium(IIl) chloride23 and methanol, followed by treatment with pyridinium p-toluenesulfonate and methanol (Scheme 16).20 The product obtained was a mixture of two stereoisomers of the methoxyl group at the 4-position, from which a single isomer 75 was isolated as... 

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