Glyoxal is efficiently transformed into the chiral aminals bearing the hydrazone functionality 2a and 2b. These compounds react under complete diastereocontrol with various organolithium reagents, affording chiral hydrazines 3-9. Reduction with Raney nickel leads to aminal protected alpha-aminoaldehydes, which, in turn, are easily hydrolyzed to the free chiral aldehydes (after tBoc protection of the amine).
Chiral Aminal Templates: Diastereoselective Addition to Hydrazones; An Asymmetric Synthesis of α-Amino Aldehydes
作者:Alex Alexakis、Nathalie Lensen、Jean-Philippe Tranchier、Pierre Mangeney、J. Feneau-Dupont、J. P. Declercq
DOI:10.1055/s-1995-4042
日期:1995.8
The monohydrazone of glyoxal may be derivatized into a chiral aminal with diamine 7. The resulting chiral reagent 13 reacts with complete diastereocontrol with organolithium reagents in THF. This sterically controlled reaction may be altered to chelation control by using Grignard reagents in toluene, affording the opposite diastereomer in excellent de. The N-N bond of the hydrazine functionality is then cleaved with Raney nickel, assisted by ultrasound. After protection of the resulting primary amino functionality, the aminal is hydrolyzed to afford the desired α-amino aldehydes without epimerization. The same reaction sequence, without cleavage of the N-N bond, affords an α-hydrazino aldehyde.