A Simple Synthesis of the Indole Alkaloid Yuehchukene

The alkaloid yuehchukene 1 is a potent anti-fertility agent and has recently been synthesised in 10% yield by treatment of 3-isoprenylindole with silica gel and benzene containing a catalytic amount of trifluoroacetic acid. 

Treatment of l-(3, 4 -methylenedioxybenzyl)-2-methyl-6,7-dimethoxyisoquinolinium iodide with lithium aluminium hydride in ether followed by immediate treatment with 2N hydrochloric acid resulted in formation of an intense red-violet colour which very quickly faded to yellow. Basification of the reaction mixture and extraction with chloroform gave an oil which was reduced by treatment with sodium borohydride in ethanol. This gave a product which was isomeric with, but different from, l-(3 ,4 -methylenedioxybenzyl)-2-methyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, the expected product from this sequence of reactions. 

Suggest a structure for the unexpected product and give a reasonable mechanism for its formation. 

When 3-(4-j -tolyloxybut-2-ynyloxy)[l]benzopyran-2-one 1 was heated under reflux in carefully purified chlorobenzene, the exclusive product, formed in 92% yield, was 1 -(p-tolyloxymethyl)pyrano[2,3-c][l]benzopyran-5(3i/)-one 2. The compound 2 was also the exclusive product when either xylene or ethylbenzene was used as solvent. However, when 1 was heated under reflux in chlorobenzene containing a catalytic amount of AIBN, 2 was obtained in 20% yield together with 80% of 2-methyl-l-(p-tolyloxymethyl)furo[2,3-c] [l]benzopyran-4-one 3. The compound 3 was the exclusive product when PEG-600, IV.lV-dimethylaniline, pyridine or ethylbenzene containing a catalytic amount of p-TsOH was used as solvent, the yields being 90,90, 80 and 90% respectively. 

---