Efficient Synthesis of Tetrahydroxylated Pyrrolizidines by Nitrone Cycloaddition Leading to Unnatural Stereoisomers of 7-Deoxycasuarine
作者:Lubor Fišera、Gabriel Podolan、Lucia Kleščíková、Jozef Kožíšek、Marek Fronc
DOI:10.1055/s-0030-1260933
日期:2011.7
A convenient and efficient method has been used for the synthesis of ten new tetrahydroxylated pyrrolizidines 12a,b, 13a-c, 14a,b, and 15a-c starting from sugar-derived cyclic nitrones prepared from d-xylose, d-arabinose, d-ribose, and l-arabinose, through a five-step reaction sequence. Pyrrolizidine 12a is an enantiomer of 7-deoxycasuarine and pyrrolizidine 12b an enantiomer of the as yet unknown 7-deoxyuniflorine A. This method expands the scope of nitrone cycloadditions and is flexible enough for the synthesis of various stereoisomers of highly polyhydroxylated pyrrolizidines.
通过五步反应序列,从由d-木糖、d-阿拉伯糖、d-核糖和l-阿拉伯糖制备的糖源环状硝酮出发,采用了一种便捷高效的方法来合成十种新的四羟基吡咯烷啶12a、b、13a-c、14a、b和15a-c。吡咯烷啶12a是7-脱氧木槿碱的对映异构体,吡咯烷啶12b是未知的7-脱氧单花素A的对映异构体。这种方法扩大了硝酮环加成反应的范围,并且具有足够的灵活性,可用于合成高度多羟基吡咯烷啶的各种立体异构体。