Generation and Properties of N7-Xanthinium Ylides : Reactions of N7-Xanthinium Ylides with Diphenylcyclopropenone and Acetylenic Compounds

Xanthinium N7-ylides were generated in situ from 7-substituted 9-methylxanthinium tosylates (2) using n-BuLi in tetrahydrofuran or Et3N in MeCN. The xanthinium N7-ylides (3) generated using Et3N in MeCN reacted with diphenylcyclopropenone to give pyrone derivatives and isocaffeine in good yields. The reactions of 3a-b with dimethyl acetylenedicarboxylate or methyl propiolate (MP) afforded 5-pyrrol-1-yluracils in moderate yields. N7-Methoxycarbonylmethylide (3c) reacted with MP to give a pyrrolopteridine derivative together with a 5-pyrrol-1-yluracil derivative. Furthermore, the dihydropyrrolopurine derivative (7), a primary 1, 3-dipolar cycloaddition product, was detected by nuclear magnetic resonance measurement of the products.