[Development of radical reactions in water aimed at environmentally benign synthetic reactions]

The aqueous medium radical reactions of a variety of imine derivatives such as oxime ether, oxime, hydrazone, nitrone, and N-sulfonylimine were investigated. Triethylborane-mediated intermolecular alkyl radical addition to glyoxylic oxime ether, oxime, and nitrone in water proceeded smoothly to give alpha-amino acid derivatives in good yields. Alkyl radical addition to N-sulfonylimine proceeded in aqueous media using zinc as a radical initiator. The zinc-mediated radical reaction of the hydrazone with a chiral camphorsultam provided the corresponding alkylated products with good diastereoselectivities, which could be converted into enantiomerically pure alpha-amino acids. The indium-mediated radical reactions provide new opportunities for carbon-carbon bond formation such as alkylation reactions of imines and 1,4-addition to electron-deficient olefins. The indium-mediated tandem reactions also proceeded effectively via two carbon-carbon bond-forming processes for the preparation of various types of functionalized cyclic compounds.