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.
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.