Synthesis of Tetrahydrokuwanon C Tetramethyl Ether

As mentioned in the preceding section, morusin (24), cyclomoru-sin (30), compound A (31), kuwanon C (33), and oxydihydromorusin (34) were correlated as shown in Fig. 7. Structures were confirmed 

48 and 2,4-dimethoxybenzoyl chloride by the Baker-Venkataraman method (52) was identical with tetrahydrokuwanon C tetramethyl ether (33 a) obtained from kuwanon C (33). These results confirmed the structures of morusin, cyclomorusin, compound A, kuwanon C, and oxydi-hydromorusin as 24, 30, 31, 33, and 34, respectively (Fig. 10). 

As mentioned earlier, Deshpande et al had reported the isolation and structure determination of four flavones with isoprenoid substituents from Morus alba root bark, mulberrin (1), mulberrochro-mene (2), cyclomulberrin (3), and cyclomulberrochromene (4) (20). The difference between the flavones with isoprenoid substituents isolated by Deshpande et al. and those, such as morusin (24), cyclomorusin (30), and kuwanon C (33), isolated by our group is lay in the mode of attachment of the C5 unit to ring A. 

In order to clarify these points, we studied the C-NMR spectra of morusin (24) and related flavonoids with isoprenoid substituents 

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