Umpolung of Organometallic Compounds by Electrochemical Reactions and Its Applications to Carbon-Carbon Bond Formation

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We have found that anodic oxidation of alpha-heteroatom-substituted organotin compounds results in the cleavage of the C-Sn bond and the introduction of a nucleophile onto the carbon. Therefore, the electrochemical oxidation provides an efficient method for"umpolung"of organotion compounds.On the basis of this reaction we have developed intermolecular and intramolecular carbon-carbon bond formation reactions which provide useful tools in organic synthesis.For example, the anodic oxidation of alpha-stannyl ethers and carbamates containing carbon-carbon double bonds lead to effective cyclization. A fluorine atom is introduced onto one of the original olefinic carbons in the cyclized product, indicationg that fluoride ion from Bu_4NBF_4 (supporting electrolyte) attacked the cyclized cation as nucleophile. Bu_4NPF_6 was also found to be effective as the fluoride source. The present method is generally applicable to endo cyclization to form six- and seven-membered rings. Endo cyclization to form a five-membered ring was not successful. The methord outlined here is a new approach to both electrochemical carbon-carbon bond formation and the synthesis of fluorine-containing compounds.We have also developed an intermolecular carbon-carbon bond formation. The anodic oxidation of alpha-heteroatom substituted organotin compounds in the presence of allylsilanes or silyl enol ethers as carbon nucleophiles also proceeds smoothly to give the corresponding coupling products.The reactions we have developed in this project provide new aspects of organometallic chemistry and electro-organic chemistry.