Chiral Aminal Templates: Diastereoselective Addition to Hydrazones; An Asymmetric Synthesis of α-Amino Aldehydes

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Abstract
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.

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