Abslrack N-9 and N-7 bemylated M&@IKS redly pnrticipate in palladium catalyzed cmsa wuplingreactionswithogurocinaiwJ~ dwivaiivcs. J.Ilmostillaacmthc6chloroplrims canbe.used. organosmMane 8 are excellent reagent8 for the intmduction of alkenyl and aryl ~ts,~t~orgameinccompoundprmeIhe~~of~~fortheiDlhodnchion~alLylgroupp.
We recently reported that 64loropurines participate iu palladium catalyzed cross coupling reactions with organostanuaues, allowing smooth iutroduction of alkenyl-aud aryl substituents in the purine 6position.1 No protection of the mhuively acidic purine ring NH function was required. This reaction, the so called Stille reaction? has been extensively applied for carbon -carbon bond formation in heterocycles.3 hut the reaction has received little attention in purine chemistry. Apart from the work described above, coupling of N-9 alkylated 24xlopurines has been studied4 and recently a few examples of N-9 alkylated 64odo-and 8-bromopurines as substrates appeared. 4~ Our finding that readily available 6-chloropurines are reactive enough to participate in Stille type reactions and the fact that diverse biological effects are reported for modified purine nucleosides, led us to explore the reactivity of N-alkylated 6-chloropurines in palladium catalyzed cross couplings.
We herein report on the reactivity of both N-9 and N-7 benxylated 6chloropurines in the Stille reaction. Furthermore, we report, to the best of our knowledge, the first examples of couplings between halopurines and organoxiuc reagents.
RE!WLTS AND DISCUSSION
6Chloropurine 15 was N-alkylated with benxyl chloride in the presence of potassium carbonate. DMF was the solvent of choice (Scheme 1).