Synthesis of a series of ω-dimethylaminoalkyl substituted ethylenediamine ligands for use in enantioselective catalysis
作者:Subrata K. Ghosh、Carola Ganzmann、John A. Gladysz
DOI:10.1016/j.tetasy.2015.09.012
日期:2015.12
The title compounds H2NCH((CH2)(n)NMe2)CH2NH2 L1-1A (n = 1-4) are efficiently synthesized in enantiopure form. The commercial starting materials, L-asparagine, (S)-5-hydroxymethy1-2-pyrrolidinone, and (S)-6-(((benzyloxy)carbonyI)-amino)-2-((tert-butoxycarbonyl)amino)hexanoic acid, are elaborated in 6-9 standard steps to giye Ll (18% overall), 12 (13%), L3 (36%) and LA (38%) or the corresponding tris(hydrochloric acid) salts [H3NCH((CH2)(n)NHMe2)CH2NH3](3+) 3Cl(-), which are preferable for long term storage. The sequences make use of isobutyl carbamate, Cbz, and Boc protecting groups and Hofmann type rearrangements; the dimethylamino groups are introduced at late stages, either via reductive dimethylations or nucleophilic displacements involving mesylates and HNMe2. L1-L4 chelate to [Co(en)(2)](3+) fragments to give octahedral complexes that catalyze numerous enantioselective reactions. (C) 2015 Elsevier Ltd. All rights reserved.