Efficient Synthesis of Tetrahydroxylated Pyrrolizidines by Nitrone Cycloaddition Leading to Unnatural Stereoisomers of 7-Deoxycasuarine

[摘要]：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.

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