作者:Peter C. Astles、Eric J. Thomas
DOI:10.1039/a606551a
日期:——
Alkylation of the racemic sulfone 25, available from the
epoxide 8, using the iodide 24 followed by reduction gives the
protected hydroxy acetal 27. Selective deprotection gives the
alcohol 28. This is converted into the bromide 29 which is used
to alkylate the keto phosphonate 33. Hydrolysis of the alkylated
keto phosphonate 30 gives the aldehyde 31 which is cyclised under
mild conditions (63%) and the product treated with
methylmagnesium iodide, to give the racemic thunbergols 3 and 4,
in a ratio of 3â¶4 = 10â¶90. The
laevorotatory sulfone 25 has been prepared by regioselective
ring-opening of the epoxide 38 followed by hydrogenation,
selective protection and functional group modification. After
alkylation of this sulfone using the iodide 24 and conversion
into the aldehyde 46, an asymmetric aldol condensation gives the
hydroxy amide 47 which is converted directly into the hydroxy
keto phosphonate 49 by reaction with an excess of lithiated
dimethyl methylphosphonate. After protection of the hydroxy
group, selective hydrolysis of the acetal gives the aldehyde 51
which is cyclised as before to give the naturally occurring
cembratrienediols 1 and 2 after reaction with methylmagnesium
iodide and deprotection.
使用碘化物 24 对环氧化物 8 生成的外消旋砜 25 进行烷基化,然后还原,得到受保护的羟基缩醛 27。选择性脱保护得到醇 28。再将其转化为溴化物 29,用于烷基化酮基膦酸酯 33。烷基化的酮基膦酸盐 30 经水解后得到醛 31,醛 31 在温和条件下进行环化(63%),产物经甲基碘化镁处理后得到外消旋噻吩伯醇 3 和 4,比例为 3â¶4 = 10â¶90。通过环氧化物 38 的区域选择性开环,然后进行氢化、选择性保护和官能团修饰,制备出了来沃托砜 25。使用碘化物 24 将该砜烷基化并转化成醛 46 后,通过不对称醛醇缩合得到羟基酰胺 47,再通过与过量的甲基膦酸二甲酯反应直接转化成羟基酮膦酸盐 49。在保护羟基后,选择性水解缩醛得到醛 51,醛 51 与甲基碘化镁反应并脱保护后,如前环化,得到天然的 cembratrienediols 1 和 2。