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 (NiBr(2)(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(PPh(3))(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.

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A novel, efficient, and atom-economic methodology for the preparation of a large series of diversely substituted (pyridin-2-yl)purines has been developed. Thus, microwave-enhanced [2+2+2] cyclotrimerization of 6-(diynyl)purines with nitriles in the presence of a stoichiometric or catalytic amount of [CpCo(CO) 2 ] afforded the corresponding products in good yields. The reactions carried out with various alkyl, aryl, and

Purine derivativesPurine derivatives R 0540 [2 + 2 + 2]-Co-cyclotrimerization 6-Alkynylpurines with Diynes: A Method for Preparation of 6-Arylpurines. -A series of 6-arylpurines (III)-(V) is obtained by [2 + 2 + 2]-co-cyclotrimerization of (I) with (II) in the presence of different Ni-and Co-phosphine complexes. The reaction is also applied successfully to the nucleoside derivative (VI). -(TUREK, P.; KOTORA*, M.; HOCEK, M.; CISAROVA, I.; Tetrahedron Lett. 44 (2003) 4, 785-788; Dep. Org. Nucl. Chem., Charles Univ., CZ-128 40 Prague 2, Czech Republic; Eng.) -Roy 18-136