Synfacts 2009(2): 0214-0214  
DOI: 10.1055/s-0028-1087588
Organo- and Biocatalysis
© Georg Thieme Verlag Stuttgart ˙ New York

Radical Addition to C=N Bonds Mediated by Chiral Ammonium Salts

Contributor(s): Benjamin List, Saihu Liao
D. O. Jang*, S. Y. Kim
Yonsei University, Wonju, Korea
Further Information

Publication History

Publication Date:
22 January 2009 (online)


A protonated cinchona alkaloid ­derivative (PC)-mediated enantioselective radical addition of alkyl radicals to the C=N bond of N-benzoyl hydrazones is reported (for a Lewis acid mediated version, see: G. K. Friestad et al. ­Angew. Chem. Int. Ed. 2003, 42, 5061). In the presence of PC, Ph2SiH2, Et3B and air in di­chloromethane, the addition of alkyl radicals generated from alkyl iodides to N-benzoyl hydrazones furnished the adducts in good yields and good to excellent enantioselectivities (90:10 to 99.5:0.5) at -30 ˚C. The employment of diphenylsilane instead of organotin hydrides as the radical chain carrier can avoid such disadvantages as high toxicity and difficulty in purifying the product. Triethylborane is necessary for initiating the reaction at low temperatures.