[2 + 2 + 2]‐Co‐cyclotrimerization 6‐Alkynylpurines with Diynes: A Method for Preparation of 6‐Arylpurines.

Abstract

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

[2+2+2] Cocyclotrimerization with Ferrocenylalkynes

“…A surprisingly good result was obtained with the rarely used but effective catalyst [CoBr(PPh 3 ) 3 ]. [10,13] The reaction with this complex proceeded at low temperature (20°C) to provide 3aa in 75% yield within a relatively short time. This complex was examined considering a report that a catalytic system composed of CoI 2 /2PPh 3 /Zn cyclotrimerized triynes into benzocyclic compounds.…”

“…But this disadvantage was countered by high yields of the arene 3aa (80%). Rather surprisingly, the nickel-phosphane complexes, which are known to be effective cyclotrimerization catalysts, [10,16] gave only poor yields of 3aa even after a long reaction time. Likewise, the iridium-dppe complex that has been recently reported as a highly active catalyst [12] gave 3aa in a disappointingly low yield.…”

“…There are only three reports of catalytic homocyclotrimerization of ferrocenylethyne and so we undertook a systematic investigation of the catalytic activity of transition metal complexes that could be expected to induce a smooth cocyclotrimerization of ferrocenylalkynes with diynes. Thus, we decided to assess the activity of [RhCl(PPh 3 ) 3 ], [9] [NiL 2 Br 2 ]/Zn (L 2 ϭ 2PPh 3 , [10] dppe [11] ), [{IrCl(cod)} 2 ]/dppe, [12] [CpCo(cod)]/ 2PPh 3 , [5g] and [CoBr(PPh 3 ) 3 ] [13] as the catalyst precursors for the cocyclotrimerization of ferrocenylethyne (1a) with dipropargyl malonate (2a) to 3aa (Scheme 2). The results are summarised in Table 1. [2ϩ2ϩ2] Cocyclotrimerization with Ferrocenylalkynes FULL PAPER The best yields were obtained with Rh-and Co-based catalysts.…”

Preparation of Highly Substituted 6-Arylpurine Ribonucleosides by Ni-Catalyzed Cyclotrimerization. Scope of the Reaction

“…In our previous reports, we have shown that cyclotrimerization of 6-alkynylpurines with zirconacyclopentadienes or with α,ω-diynes catalyzed by in situ generated Ni(0)-species from NiBr 2 (dppe)/Zn is a suitable method for the preparation of 9-Bn- or 9-THP protected 6-arylpurines . Herein, we wish to describe an extension of the latter methodology to the synthesis of the corresponding ribonucleosides.…”

“…Since Ni(cod) 2 /2PPh 3 − and other Ni based systems , are known to be efficient catalysts for the cyclotrimerization of various alkynes, it was desirable to compare their reactivity with the NiBr 2 (dppe)/Zn system. , Our initial study was focused on the reaction of 1a with 2a in different solvents to optimize reaction conditions. The results presented in Table show that yields of the corresponding arylpurinylglycoside 3aa rose with the increasing polarity of the solvent used.…”