Process Research and Development and Scale-up of a 4,4-Difluoro-3,3-dimethylproline Derivative

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• 作者：Francesco Rossi ; Francesco Corcella ; Francesco Saverio Caldarelli ; Franco Heidempergher ; Chiara Marchionni ; Miriam Auguadro ; Marco Cattaneo ; Lucio Ceriani ; Giuseppina Visentin ; Giambattista Ventrella
• 刊名：Organic Process Research & Development
• 出版年：2008
• 出版时间：March 2008
• 年：2008
• 卷：12
• 期：2
• 页码：322 - 338
• 全文大小：1947K
• 年卷期：v.12,no.2(March 2008)
• ISSN：1520-586X

文摘

The multikilogram production of the proline derivative 1, a key intermediate of a HIV protease inhibitor, required the design of a synthetic route able to be safely, effectively, and easily scaled up. Synthesis of the proline skeleton began with construction of racemic glycine derivative 4, via an ester enolate Claisen rearrangement of Boc-glycine 3-methyl-but-2-enyl ester (3) in the absence of a Lewis acid. After a classical resolution of 4 with (S)-phenylglycinol, (S)-4 was transformed into bromo-lactone 6b with NBS. The bromo-lactone was transformed to proline alcohol 8 via a base-promoted rearrangement involving lactone solvolysis. An NMR study suggested that a bicyclic lactone was initially formed, which subsequently opened by the methanol solvent to form 8. The requisite ketone for fluorination was prepared via oxidation of the enantiomerically pure 8, using NaClO and catalytic TEMPO. gem-Difluoro proline 1 was then prepared from the ketone via fluorination with Deoxo-Fluor. During this study it was discovered that SiO₂ promoted fluorination by Deoxo-Fluor. This study allowed the production of 7.5 kg of 1 after 10 steps, in 4.5% molar yield and high purity (94–99% HPLC assay).