Cocyclotrimerization of 6-Alkynylpurines with α,ω-Diynes as a Novel Approach to Biologically Active 6-Arylpurines

Transition metal complex catalyzed cocyclotrimerization of 6-alkynylpurines 1 with various diynes
enables the preparation of a plethora of substituted 6-arylpurines 3 in good yields. The most general
catalyst for the reaction is a user-friendly system based on a nickel−phosphine complex and
reductant (NiBr2(dppe)/Zn) in MeCN. The reaction conditions are compatible with various protective
groups on the purine moiety (Bn, THP). As far as other potential catalysts were concerned, only
CoBr(PPh3)3 showed reasonable activity in cocyclotrimerization of alkynylpurines with dipropargyl
ether. A comparison of catalytic with stoichiometric approaches and the ligand effect in the catalyst
is also given. Cytostatic activity screening of title 6-arylpurines was performed and several
moderately active compounds were found.