A simple, high-yield procedure has been developed for the ortho-lithiation and subsequent ortho-substitution of phenols by a manifold of electrophiles. N,C-Dilithiation of O-aryl N-monoalkylcarbamates proved to be impossible due to a cleavage reaction of the monolithiated intermediates. However, in situ N-silylation of O-aryl N-isopropylcarbamates proceeds smoothly with trialkylsilyl triflates N,N,N',N'-tetramethylethylenediamine (TMEDA). Separation of the formed O-aryl N-isopropyl-N-trialkylsilylcarbamates from the byproduct TMEDA·HOTf, which is insoluble in diethyl ether or toluene, is not required. ortho-Lithiation with n-butyllithiumTMEDA at 78°C leads to the corresponding aryllithium, which does not undergo anionic ortho-Fries rearrangement under the reaction conditions, but is efficiently substituted by electrophilic reagents. During the aqueous work-up, the N-silyl group is removed and the corresponding ortho-substituted O-aryl N-isopropylcarbamate is isolated. Among the introduced electrophiles are: Me3Si, Bu3Sn, PhS, I, Br, Cl, alkyl, α-hydroxyalkyl. Liberation of the free phenols is performed under mild alkaline conditions.Key words: directed ortho-metalation, ortho-lithiated O-aryl carbamates, ortho-substituted phenols, in situ protection of N-monoalkylcarbamates.
已开发出一种简单、高产率的程序,用于对苯酚进行正-锂化和随后的正-取代,通过一系列亲电试剂。O-芳基N-单烷基氨基甲酸酯的N,C-二锂化由于单锂化中间体的裂解反应而被证明是不可能的。然而,O-芳基N-异丙基氨基甲酸酯的原位N-硅烷基化与三烷基硅酰三氟甲烷(TMEDA)顺利进行。无需将形成的O-芳基N-异丙基-N-三烷基硅基氨基甲酸酯与副产物TMEDA·HOTf分离,后者在乙醚或甲苯中不溶。在-78°C下,使用正丁基锂-TMEDA进行正-锂化可得到相应的芳基锂,在反应条件下不会发生阴离子的正-Fries重排,但会被亲电试剂有效地取代。在水工作过程中,N-硅基团被去除,相应的正-取代的O-芳基N-异丙基氨基甲酸酯被分离出来。引入的亲电试剂包括:Me3Si、Bu3Sn、PhS、I、Br、Cl、烷基、α-羟基烷基。在温和的碱性条件下进行游离苯酚的操作。关键词:定向正-金属化、正-锂化O-芳基氨基甲酸酯、正-取代苯酚、原位保护N-单烷基氨基甲酸酯。