304 
as was originally assumed by Borsche, by being 
cyclic isomers (a- and y-py rones). If the new 
yangonin formula is correct, it should be possi- 
ble by hydrogenation of the two double bonds 
to transform yangonin derivatives into dihydro- 
kawain derivatives. We (Werny and Hansel, 
1963) were able to demonstrate that this is 
indeed possible. Starting with naturally occur- 
ring yangonin we obtained by catalytic hydro- 
genation p-methoxydihydrokawain, the constitu- 
tion of which was secured by an independent 
PACIFIC SCIENCE, Vol. XXII, July 1968 
synthesis. These reactions are shown in Figure j 
9. One of the two double bonds in the ring is 
not attacked under the given conditions (pal- ! 
ladium on carbon in ethyl acetate). This agrees 1 
with the observation that enol-ether double 1 
bonds are catalytically hydrogenated only with 
difficulty. 
The actual cause, that is the mechanism, of the | 
phenomenon which led Borsche to the wrong 
formulation of yangonin is still not known. Why 
is the enol-methyl ether of yangonin readily 1 
5.6.78 - tetrohydroyangon in 
Fig. 9- Transformation of yangonin in 5.6.7.8-tetrahydroyangonin and its identity with synthetic (±) p- 
methoxy-7.8-dihydrokawain (Werny and Hansel, 1963). 
