Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 17.1 Preparation of aliphatic amino acid derived γ-alkoxycarbonylamino-β-oxo ylides and pyrolysis to give α,β-acetylenic γ-amino acid and GABA analogues
作者:R. Alan Aitken、Nazira Karodia、Tracy Massil、Robert J. Young
DOI:10.1039/b110243e
日期:2002.2.6
A series of eleven α-aminoacyl stabilised phosphorus ylides 9â19 have been prepared by condensation of N-alkoxycarbonyl protected amino acids with Ph3PCHCO2Et using a carbodiimide peptide coupling reagent. Upon flash vacuum pyrolysis at 600 °C, these undergo extrusion of Ph3PO to give the corresponding α,β-acetylenic γ-amino esters 21â29, 33 and 34 in moderate yield. In two cases the terminal alkynes 30 and 31 are also formed. The β-aminoacyl ylide 20 from β-alanine
similarly gives the α,β-acetylenic δ-amino ester 35 upon pyrolysis. Regioselective addition of HBr to the triple bond of one acetylenic ester 25 was observed giving a mixture of E and Z
α-bromoacrylates 36. Hydrogenation of the N-Cbz acetylenic esters 21â23 and 33 results in N-deprotection and hydrogenation of the triple bond to afford the chiral GABA analogues 37â40 in 70 â>95% ee as determined by 19F NMR of their Mosher amides. Fully assigned 13C NMR spectra of all the ylides and acetylenic ester derivatives are presented.
通过使用羰二亚胺肽偶联试剂,将N-烷氧羰基保护的氨基酸与Ph3PCHCO2Et缩合,制备了一系列十一种α-氨基酰稳定的膦叶立德9〜19。在600°C下进行闪蒸真空热解,它们会排出Ph3PO,以中等产率得到相应的α,β-炔基γ-氨基酯21〜29、33和34。在两种情况下,还形成了末端炔烃30和31。来自β-丙氨酸的β-氨基酰膦叶立德20在热解时同样生成α,β-炔基δ-氨基酯35。观察到HBr对一个炔基酯25的三键的选择性加成,得到E和Z α-溴丙烯酸酯36的混合物。对N-Cbz炔基酯21〜23和33的氢化导致N-脱保护和三键的氢化,以70〜>95%的ee提供手性GABA类似物37〜40,这由它们的Mosher酰胺的19F NMR确定。给出了所有膦叶立德和炔基酯衍生物的全分配13C NMR谱。