Regioselectivity in Cross-Coupling Reactions of 2,6,8-Trichloro-9-(tetrahydropyran-2-yl)purine: Synthesis of 2,6,8-Trisubstituted Purine Bases
作者:Michal Hocek、Radek Pohl
DOI:10.1055/s-2004-834881
日期:——
The regioselectivity of cross-coupling reactions (Pd-catalyzed Suzuki-Miyaura reactions with phenylboronic acid and Fe-catalyzed reactions with methylmagnesium chloride) of 2,6,8-trichloro-9-(tetrahydropyran-2-yl)purine with varying amounts of the organometallic reagent was studied. In general, the regioselectivity of these reactions was quite low giving mixtures of isomers of mono-, di- and trisubstituted products. Nevertheless, 2,6-dichloro-8-methyl-9-THP-purine (1aab), 2-chloro-6,8-dimethyl-9-THP-purine (1abb) and 2,8-dichloro-6-phenyl-9-THP-purine (1aca) were isolated in acceptable yields and used as intermediates for further cross-coupling reactions giving a series of 2,6,8-trisubstituted 9-THP-purines that were deprotected to the corresponding purine bases. Characteristic 13C NMR shifts of CH3 or ipso-Ph carbons in different positions of the purine ring have been observed enabling rapid and facile identification of the particular isomer.
研究了 2,6,8-三氯-9-(四氢吡喃-2-基)嘌呤与不同量的有机金属试剂发生交叉偶联反应(钯催化的与苯硼酸的铃木-宫脲反应和铁催化的与甲基氯化镁的反应)的区域选择性。一般来说,这些反应的区域选择性很低,会产生单取代、二取代和三取代产物的异构体混合物。不过,2,6-二氯-8-甲基-9-THP-嘌呤(1aab)、2-氯-6,8-二甲基-9-THP-嘌呤(1abb)和 2,8-二氯-6-苯基-9-THP-嘌呤(1aca)以可接受的产率分离出来,并用作进一步交叉偶联反应的中间体,得到一系列 2,6,8-三取代的 9-THP-嘌呤,这些嘌呤被脱保护为相应的嘌呤碱。在嘌呤环的不同位置观察到 CH3 或 ipso-Ph 碳的特征性 13C NMR 移动,从而能够快速、简便地识别特定的异构体。