ACTIVATION OF METALS AND THEIR UTILIZATION FOR ORGANIC SYNTHESIS

点击翻译按钮获取中文摘要

The following stereoselective organic transformations have developed with an activated manganese matal or chromium (II). (1) Treatment of 1-iodoalkyl triethlsilyl ether, derived from an alkanal and EtィイD23ィエD2SiI in dichloromethane, with a mixture of manganese and PbCIィイD22ィエD2 in THF generates a nonstabilized carbonyl ylide. The ylide reacts with unsaturated compounds, such as α, β-unsaturated esters, allylic ethers, and an aldehyde, to give tetrahydrofuran derivatives (or a dioxolane) via [3+2] cycloadditon reactions. (2) The mild reluctant chromium (II) chloride can discriminate between alkyl iodides, alkyl radicals, and allylic radicals. In the presence of chromium (II) the alkyl radical is so long-lived that it can undergo intermolecular addition to a 1, 3-diene. Rapid one-electron reduction of the formed allylic radical results in an allylic chromium species, which adds to an aldehyde to afford a three-component coupling product. (3) Treatment of α-chloroalkylboronic esters with CrCIィイD22ィエD2 in the presence of LiI and TMEDA generates α-boryl radicals, which add to α, β-unsaturated esters in a 1, 4-fashion under mild conditions in excellent yields. (4) A chromium hydride equivalent generated from CrCIィイD22ィエD2, BィイD212ィエD2, and water reacts regioselectively with 1, 3-dienes to give allylic chromium reagents, and the reagents add to carbonyl compounds in a chemo- and stereoselective manner. (5) A catalytic cycle of a chromium salt in a stereoselective transformation of aldehydes to (E)-1-iodoalknens using a geminal dichromium reagent, is assembled with zinc, MeィイD23ィエD2SiCI, and NaI in dioxane. (6) Iodoform is reduced with manganese in the presence of MeィイD23ィエD2SiCI to give MeィイD23ィエD2SiCHIィイD22ィエD2. A one-pot transformation of aldehydes to (E)-1-alkenyltrimethylsilanes is then performed with iodoform, manganese, MeィイD23ィエD2SiCI, and a catalytic amount of chromium(II) chloride in THF via in situ formation of MeィイD23ィエD2SiCHIィイD22ィエD2.