Total synthesis and structural elucidation of ent-micropyrone and (+)-ascosalipyrone
作者:Claire Gregg、Michael V. Perkins
DOI:10.1039/c2ob25501d
日期:——
The total synthesis of 6-[(1S,3S)-1,3-dimethyl-2-oxopentyl]-4-hydroxy-3,5-dimethyl-2H-pyran-2-one (22), the enantiomer of the natural product micropyrone (1), was achieved in 9 linear steps (10% overall yield), from Evans auxiliary (R)-12 with key coupling of the dianion of dione 17 and aldehyde 11. Formation of the pyrone ring and subsequent oxidation at C7 was achieved without epimerization of the sensitive position α to both the pyrone ring and the carbonyl. The same sequence using the alternate dione 24 achieved the total synthesis of 6-[(1S,3S)-1,3-dimethyl-2-oxopentyl]-4-hydroxy-3-methyl-2H-pyran-2-one (28), the (+)-enantiomer of the natural product, ascosalipyrone (2). In both cases diastereomeric aldehydes 11 and 16 were taken through the synthetic sequence to give two possible diastereomers of the natural products. Comparison of the 1H and 13C NMR data for the synthetic isomers with that reported for the natural products determined their relative stereochemistry. Comparison of the optical rotation obtained for 22 established it to be the enantiomer of micropyrone.
从伊文思助剂 (R)-12,通过二酮 17 和醛 11 的二酐键偶联,经过 9 个线性步骤(总收率 10%)实现了 6-[(1S,3S)-1,3-二甲基-2-氧代戊基]-4-羟基-3,5-二甲基-2H-吡喃-2-酮(22)的全合成,该化合物是天然产物微吡喃酮(1)的对映体。吡酮环的形成和随后在 C7 处的氧化在敏感位置 α 与吡酮环和羰基发生表聚的情况下得以实现。使用替代二酮 24 的相同步骤实现了 6-[(1S,3S)-1,3-二甲基-2-氧代戊基]-4-羟基-3-甲基-2H-吡喃-2-酮 (28) 的全合成,这是天然产物升水吡喃酮 (2) 的(+)-对映体。在这两种情况下,非对映醛 11 和 16 都是通过合成序列得到天然产物的两种可能的非对映异构体。将合成异构体的 1H 和 13C NMR 数据与报告的天然产物的 1H 和 13C NMR 数据进行比较,确定了它们的相对立体化学结构。通过比较 22 的旋光度,确定了它是微吡喃酮的对映体。