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Enantioselective Preparation of γ ‐Amino Acids and γ ‐Lactams from Nitro Olefins and Carboxylic Acids, with the Valine‐Derived 4‐Isopropyl‐5,5‐diphenyl‐1,3‐oxazolidin‐2‐one as an Auxiliary
Author(s) -
Brenner Meinrad,
Seebach Dieter
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19991215)82:12<2365::aid-hlca2365>3.0.co;2-#
Subject(s) - chemistry , isopropyl , enantioselective synthesis , valine , nitro , amino acid , stereochemistry , organic chemistry , biochemistry , catalysis , alkyl
Titanium enolates of acyl‐oxazolidinones 1 , derived from acetic, propanoic, 3‐methylbutanoic, and 4‐methylpentanoic acids and 4‐isopropyl‐5,5‐diphenyl‐1,3‐oxazolidin‐2‐one, are added to aliphatic and aromatic nitro olefins in the presence of TiCl 4 ( Schemes 2 – 4 ). The products, 4‐nitro carboxylic‐acid derivatives 2 , are formed in high diastereoselectivities (ds 80 to >99%) and in good yields (50 – 75% of purified samples of ds >98%). Hydrogenation over Raney ‐Ni of the NO 2 group in the adducts leads directly to the corresponding γ ‐lactams ( 3 and 8 ; 80 – 92%), with recovery of the insoluble auxiliary ( ca . 95%). Ring opening is achieved through the N ‐Boc‐lactams ( 4 ), which are converted to N ‐Boc‐protected γ ‐amino acids 5 or to their benzyl and methyl esters ( 6 and 7 ; Scheme 5 ). The configuration of the products (containing up to three new stereogenic centers; Scheme 1 ) is assigned by comparison with literature data, by X‐ray crystal‐structure analysis (for 2c , g , f , 8 , Fig .), and by analogy. Thus, the ( S )‐auxiliary gives rise to combination of the trigonal centers of enolate and nitro olefin with Si / Si topicity (relative topicity all ‐ lk ; cf . A ).