Short Synthesis of Methylphenidate and Itsp-Methoxy Derivative
摘要:
A short method for the preparation of racemic threo- and erythro-methylphenidate derivatives is described. Condensation between a-ethoxy carbamate 1 and silyl ketene acetals 2a-b in the presence of TESOTf (20 mol%) afforded a 1.5:1 mixture of carbamates 3a-b/4a-b. Hydrogenolysis in EtOH followed by treatment with 3N HCl/MeOH afforded the corresponding hydrochlorides 7a-b/8a-b in good yields.
Solid-Phase Synthesis of Piperidines by N-Acyliminium Ion Chemistry
摘要:
An efficient solid-phase procedure for the synthesis of a number of 2-substituted piperidines is reported. Starting from solid-supported carbamate-tethered delta-amino acetals, 2-benzotriazolyl-substituted (Bt-substituted) piperidines were obtained by acid-induced ring-closure followed by trapping of the transient N-acyliminium ions with benzotriazole. These 2-Bt-substituted piperidines were then used as precursors for the successful introduction of several C-nucleophiles by N-acyliminium. ion chemistry. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
The stereochemistry of the addition of titanium enolates of N-propionyl-oxazolidin-2-ones to 5- and 6-membered N-acyliminium ions
作者:Ronaldo A. Pilli、Conceição de Fátima Alves、Maria Alice Böckelmann、Yvonne P. Mascarenhas、J. Geraldo Nery、Ivo Vencato
DOI:10.1016/s0040-4039(99)00398-6
日期:1999.4
The stereochemistry of the addition of the N-propionyl titanium enolates 2a and 2b to 5- and 6-membered 2-ethoxycarbamates 1a-f was investigated. The addition proceeded stereoselectively to afford the corresponding (2S,1′S)-2-substituted pyrrolidines as the major diastereoisomer. Despite the lack of reactivity between 2-ethoxypiperidines 1b and N-propionyl titanium enolates 2a and 2b, less bulky carbamate