Rhodium-Catalyzed Asymmetric Hydrohydrazonemethylation of Styrenes: Access to 
Chiral Hydrazones, Hydrazides, Hydrazines and Amines

Kliemann, Max N.; Teeuwen, Simon; Weike, Christopher; Francio, Giancarlo; Leitner, Walter

doi:10.1002/adsc.202200804

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Rhodium-Catalyzed Asymmetric Hydrohydrazonemethylation of Styrenes: Access to Chiral Hydrazones, Hydrazides, Hydrazines and Amines

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Leitner, Walter
Research Department Leitner, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Citation

Kliemann, M. N., Teeuwen, S., Weike, C., Francio, G., & Leitner, W. (2022). Rhodium-Catalyzed Asymmetric Hydrohydrazonemethylation of Styrenes: Access to Chiral Hydrazones, Hydrazides, Hydrazines and Amines. Advanced Synthesis & Catalysis, (364), 4006-4012. doi:10.1002/adsc.202200804.

Cite as: https://hdl.handle.net/21.11116/0000-000C-83C9-D

Abstract

The catalytic asymmetric hydroformylation of styrenes was combined with condensation of the resulting aldehydes with acetohydrazide as nucleophile leading to gamma-chiral N'-substituted acetohydrazones. This cascade reaction is called hydrohydrazonemethylation (HHM) in analogy to similar hydroformylation/condensation sequences. The catalyst was formed in situ from the commercially available chiral phosphine-ligand (R,R)-PhBPE and [Rh(acac)(CO)(2)] and used at a loading of 0.2 mol%. The stable condensation products are not prone to tautomerization providing versatile chiral intermediates. Their one-pot reduction with DMAB/TsOH resulted in the corresponding gamma-chiral N'substituted acetohydrazides (14 examples) with yields ranging from 73% to 91% and enantioselectivities from 77% to 97% ee. Deprotection of the acetohydrazides led to the corresponding beta-chiral hydrazines. Reduction and hydrogenolysis of the hydrazones over Raney-Ni yielded the corresponding beta-chiral primary amines with 95% ee. Diastereoselective functionalization of the C=N bond of the hydrazones is a further synthetic option, as demonstrated by allylation with (allyl)SiCl3.