The Michael addition of a chiral amine [(-)- 6] to alpha,beta-unsaturated esters ( 4) was attained and the stereoselectivity was inverted by changing the solvent from diethyl ether to tetrahydrofuran when alpha,beta-unsaturated esters having an aromatic ring at the beta-position were employed. In addition, the chiral auxiliary in the Michael adducts ( 9A) was facilely removed with N-iodosuccinimide
Acylation of β-Amino Esters and Hydrolysis of β-Amido Esters: <i>Candida antarctica</i>
Lipase A as a Chemoselective Deprotection Catalyst
作者:Harri Mäenpää、Liisa T. Kanerva、Arto Liljeblad
DOI:10.1002/cctc.201501381
日期:2016.3.18
tert‐butyl esters of 3‐amino‐3‐phenylpropanoic acid (E>100), 3‐amino‐4‐methylpentanoic acid (E>100) and 3‐aminobutanoic acid (E=60) on 1.0–2.0 m scale. With the N‐acylated resolution products, the exceptional ability of CAL‐A to hydrolyse amides and bulky tert‐butyl esters was then studied. In all N‐acylated tert‐butyl esters, chemoselectivity favoured the amide bond cleavage. The tert‐butyl ester bond was
An asymmetric ammonia synthon for Michael additions
作者:Joel M. Hawkins、Timothy A. Lewis
DOI:10.1021/jo00033a037
日期:1992.3
The highly diastereoselective 1,4-addition of lithiated chiral amine 1 to alpha,beta-unsaturated esters, followed by hydrogenolysis of the benzylic-type C-N bonds of the 1,4-adducts, provides an asymmetric ammonia synthon for Michael additions. Under optimized conditions, lithiated 1 adds to alpha,beta-unsaturated tert-butyl esters in dimethoxyethane at -63-degrees-C in high yield with very high diastereoselectivity. Small, large, functionalized, and chiral beta-ester substituents are amenable, with (S)-1 consistently adding to (E)-3 from the top as drawn in Table II. Hydrogenolysis liberates the beta-amino esters with typically 95-99% ee.