Stereoselective Synthesis of Polysubstituted Tetrahydrofurans by Radical Cyclization of Epoxides Using a Transition-Metal Radical Source. Application to the Total Synthesis of (±)-Methylenolactocin and (±)-Protolichesterinic Acid
摘要:
Radical cyclization reactions of substituted alpha-(prop-2-ynyloxy) epoxides using bis(cyclopentadienyl)-titanium(III) chloride as the radical source resulted in polysubstituted tetrahydrofurans. Titanium(III) species were prepared in situ from commercially available titanocene dichloride and zinc dust in tetrahydrofuran, Upon radical cyclization, 2-aryl epoxides 3a-e afforded only trans products 4a-e whereas the 2-alkyl epoxides 3f-h formed a mixture of isomeric products 4f-h in a ratio of 5:1. Some of the aryl tetrahydrofuran derivatives have already been used for the synthesis of bioactive furofuran lignans. 2-Pentyl-3-(hydroxymethyl)-4-methylenetetrahydrofuran (4f) and 2-tridecyl-3-(hydroxymethyl)-4-methylenetetrahydrofuran (4g) have been transformed to two antitumor antibiotics (+/-)-methylenolactocin (1f) and (+/-)-protolichesterinic acid (1g), respectively, in good overall yield.
The title complex oxidizes primary and secondary alcohols to the corresponding carbonyl compounds. Stereoselective epoxidation of allylic alcohols is also described.
标题络合物将伯醇和仲醇氧化为相应的羰基化合物。还描述了烯丙醇的立体选择性环氧化。
Stereoselective Epoxidation of Allylic Alcohols and Dehydrogenative Oxidation of Secondary Alcohols by Means of<i>t</i>-Butyl Hydroperoxide and Aluminium Reagents
作者:Kazuhiko Takai、Koichiro Oshima、Hitosi Nozaki
DOI:10.1246/bcsj.56.3791
日期:1983.12
of a solution of geraniol and (t-BuO)3Al in benzene with t-BuOOH at 5 °C gives (2R*, 3R*)-2,3-epoxy-3,7-dimethyl-6-octenyl acetate in 83% yield after acetylative workup. Eight allylic alcohols are converted to α,β-epoxy alcohols in preparative yields. The epoxidation of secondary (E)-allylic alcohols shows opposite stereoselectivities to t-BuOOH–VO(acac)2 system. Asymmetric epoxidation with a chiral
在 5 °C 下用 t-BuOOH 处理香叶醇和 (t-BuO)3Al 在苯中的溶液,得到 (2R*, 3R*)-2,3-epoxy-3,7-dimethyl-6-octenyl acetate in 83乙酰化处理后的 % 产率。八种烯丙醇以制备产率转化为α,β-环氧醇。仲 (E)-烯丙醇的环氧化显示出与 t-BuOOH-VO(acac)2 系统相反的立体选择性。用手性异羟肟酸作为配体的不对称环氧化产生不令人满意的对映体过量程度。同样的系统也可以将仲醇以极好的收率转化为酮,而伯醇反应非常缓慢。
Selective oxidation with t-butyl hydroperoxide and aluminium reagents
作者:Kazuhiko Takai、Koichiro Oshima、Hitosi Nozaki
DOI:10.1016/s0040-4039(00)77778-1
日期:1980.1
Stereoselective epoxidation of allylic alcohols is achieved with organoaluminium peroxides. Transformation of secondary alcohols to ketones with same reagents is also disclosed.
用有机铝过氧化物可以实现烯丙基醇的立体选择性环氧化。还公开了用相同的试剂将仲醇转化为酮。
Reaction of cyanotrimethylsilane with oxiranes under Yb(CN)3 catalysis