D. A. Evans, N Finney Hydrazone Transformations-3 Chem 206 Tosylhydrazones- Better Than Hydrazones R|clH NaOAC3H20 =NNHTs+ N一NH Tosylhydrazones are isolable, stable, and easily prepared The presence of the tosyl leaving group strongly biases the system towards polar reaction pathways under hydridic reducing conditions R Ts CHO NHTS LAH (XS) R-C-N一 C-N-NH THF,△ G W. Kabalka, et al. J. Org. Chem. 1975, 40, 1834 Another Interesting Leaving Group H/H2O Ph LAH OI L. Caglioti, M. Magi Tetrahedron 1963, 19, 1127 -stilbene Further refinements Very mild reduction with NaBH3CN under slightly acidic conditions(pH 4-5) No reduction in the absence of acid; carbonyl, nitro, nitrile FGs unaffected Aromatic, sterically hindered carbonyls very poor substrates A R. Chamberlin, et al. Tetrahedron Lett. 1991, 32, 1691 laBH3 CN, CH3 COz NHTS R.O. Hutchins et al. JATsNHNH2 LAH (xs) THF, D THF, D CHO N NHTs H N N Ts H CH3 H N NHTs H N N – H R C R NNHTs Me H – Me N N Ph Ph OR B RO NH Ts C N H R R OAc O BH O R–H R C R H N NH Ph Ph N N R Me Me R C R H N B NH Ts RO OR –N2 C H H R R NaOAc•3H2O Ph Ph N N R Me Me N N R Hydrazone Transformations-3 Chem 206 – – L. Caglioti, M. Magi Tetrahedron 1963, 19, 1127. –Ts– H + /H2O Tosylhydrazones – Better Than Hydrazones Tosylhydrazones are isolable, stable, and easily prepared. The presence of the tosyl leaving group strongly biases the system towards polar reaction pathways under hydridic reducing conditions. Further Refinements Very mild reduction with NaBH3CN under slightly acidic conditions (pH 4-5). No reduction in the absence of acid; carbonyl, nitro, nitrile FGs unaffected. Aromatic, sterically hindered carbonyls very poor substrates. NaBH3CN, CH3CO2H 94% R. O. Hutchins, et al. JACS 1973, 95, 3662. 59% G. W. Kabalka, et al. J. Org. Chem. 1975, 40, 1834. – + -stilbene LAH A. R. Chamberlin, et al. Tetrahedron Lett. 1991, 32, 1691. Another Interesting Leaving Group D. A. Evans, N. Finney