|Budget Amount *help
¥6,500,000 (Direct Cost : ¥6,500,000)
Fiscal Year 1996 : ¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1995 : ¥4,600,000 (Direct Cost : ¥4,600,000)
Metals are covered with thin but tightly bound oxide layrs on its surface. In order to employ such metals in organic synthesis, efficient methods for removing the oxide layrs should be developed.
Metal-oxide layrs of manganese metal surface is effectively removed by treatment with Me_3SiCl, and a catalytic amount of PbCl_2 activates the manganese metal amazingly. Reformatsky-type reaction and allylation of carbonyl compounds are performed with the activated manganese metal. In sddition, three-component coupling reactions of alkyl iodides, alpha, beta-unsaturated nitriles (or esters), and carbonyl compounds are achieved in good to excellent yields with the manganese reducing system. Although the role of PbCl_2 is unclear, addition of a catalytic amount of the salt is essential for reducing the alkyl iodide.
Addition of alkyl radicals to allylic acrylates in a 1,4-fashion gives alpha-allyloxycarbonyl-substituted alkyl radicals, which produce ketene silyl acetals after one-electron reductio
n and trapping with Me_3SiCl. The 1,4-addition and successive Ireland-Claisen rearrangement take place by using alkyl iodides and the manganese-PbCl_2-Me_3SiCl system in DMF and THF.The double bond produced has E geometry as expected from the Ireland-Claisen rearrangement.
The above sequential reactions are realized by using the moderate manganese reducing system which discriminate between alkyl and alpha-alkoxycarbonyl-substituted alyl radicals.
The following stereoselective organic transformations have also been developed with low-valent chromium. (1) Synthetically useful (E) -1-alkenylboronic esters are prepared stereoselectively from aldehydes with olne-carbon extention by using a geminal dichromium reagent derived from a dichloromethylboronic ester, CrCl_2, and LiI under mild conditions. (2) By examination of the previously reported preparative methods of alkynyl- and alkenylchromium reagents in terms of a catalytic amount of nickel (II) salt, standard protocols for perparation of the chromium reagents are established. Less