Enantioselective Synthesis of (1R,4S)-1-Amino-4-(hydroxymethyl)-2-cyclopentene, a Precursor for Carbocyclic Nucleoside Synthesis
作者:Ki Hun Park、Henry Rapoport
DOI:10.1021/jo00081a019
日期:1994.1
(1R,4S)-1-Amino-4-(hydroxymethyl)-2-cyclpentene, an important precursor for the synthesis of carbocyclic nucleosides, has been prepared from D-glucono-delta-lactone in enantiomerically pure form (er > 99/1). The synthesis proceeded from the lactone via the diisopropylidene-2-amino-2-deoxymannonate and hydrolysis of the terminal isopropylidene group. Selective oxidation of the primary alcohol and esterification gave the corresponding mannarate which was deoxygenated at C5. Further transformations by regiospecific eliminative cleavage of the ketal and hydrogenation gave dimethyl (2S,3R)-2-amino-3-hydroxyadipate. Dieckmann cyclization through specific carbanion formation at C5 led to the aminohydroxy(methoxycarbonyl)cyclopentanone which was readily converted in a series of high-yielding steps to the target cyclopentene. Throughout the synthesis, stereo- and regioselectivities were strongly influenced by the sterically demanding 9-phenyl-9-fluorenyl protecting group on nitrogen.
(1R,4S)-1-氨基-4-(羟甲基)-2-环戊烯,作为合成碳环核苷的重要前体,已从D-葡萄糖内δ-乳酸酯以对映体纯形式(er > 99/1)成功制备。整个合成过程从乳酸酯出发,依次通过二异丙基亚胺-2-氨基-2-脱氧甘露酸酯,以及末端异丙基亚胺基团的水解。随后,通过选择性氧化主要醇并进行酯化,得到相应的甘露酸酯,该酸酯在C5位去氧。进一步通过对酮醇的区域特异性消除裂解和氢化反应,得到二甲基(2S,3R)-2-氨基-3-羟基己二酸酯。通过Dieckmann环化反应,形成特定的羧酸酐结构,生成氨基羟甲基(甲氧基羰基)环戊酮。一系列高产率的转化步骤使其最终转化为目标环戊烯。在整个合成过程中,氮原子上连接的空间位阻较大的9-苯基-9-芴基保护基对立体选择性和区域选择性产生了显著影响。