4-Methoxy-3-prenyl-2-quinolone

Methoxy-3-prenyl-2-quinolones were first prepared in connection with the synthesis and biosynthesis of quinoline alkaloids (Volume IX, pp. 247, 257), but soon afterward prenyl derivatives were identified as constituents of rutaceous plants (Table I). -Prenyl and O-geranyl ethers without, substituents in the 3-position of the quinoline nucleus will be discussed in Section V of this chapter. 

Furoquinoline alkaloids specifically labeled with 14C in the furan ring were required for biosynthetic studies (see Section VII of this chapter), and since existing routes produced low yields, Grundon and co-workers (195, 196) developed a more efficient synthesis from 4-methoxy-3-prenyl-2-quinolones 244-246. These compounds had previously been prepared from aromatic amines and substituted malonates, but direct allylation is more suitable for the preparation of labeled compounds, employing, for example, [14C]-3,3-dimethylallyl bromide. It was found that reaction of... 

Ptelea trifoliata is the only known source of hemiterpenoid quinoline alkaloids containing terminal double bonds, and nine compounds of this type have been isolated cf. Vols. 1—3, 5, and 7) the synthesis of two members of the group, O-methylptelefolonium iodide (26) and ptelefolone (29), has now been reported (Scheme 4). The 3-prenyl-4-methoxy-2-quinolone (24) was prepared by standard procedures and was converted with a peroxy-acid into a mixture of the dihydropyrano-quinolone (25) and the dihydrofuro-quinolone (27), Treatment of the latter with thionyl chloride and pyridine resulted in regiospecific elimination to give a terminal olefin, which afforded O-methylptelefolonium iodide (26). Successive reaction of the N-methyl-4-quinolone (28) cf. Vol. 7) with triphenyl phosphite dichloride and with pyridine resulted in an efficient synthesis of ptelefolone (29). 

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