SCHOLLKOPF Amino Acid Synthesis

SCHOllkOPF Amino Acid Synthesis Asymmetric synthesis of amino acids from dihydropyrazines(see 1st edition). 

The approach exploiting a chiral centre that is already in the synthon is effective in a number of cases. The chiral moiety in the synthon diverts a reaction at a nearby prochiral centre in favour of one enantiomer (asymmetric induction). An excellent example of the latter is the Schollkopf method (4 in Scheme 6.3, see also 5 in Scheme 6.7) hydrogenation of azlactones (3 in Scheme 6.3) using a homogeneous chiral catalyst is one route illustrating the former approach. Use of chiral five-membered heterocyclic compounds (e.g., 6 and 7) offers an alternative successful approach to asymmetric amino-acid synthesis. 

Schollkopf Bis-Lactim Amino Acid Synthesis Schopf (see Robinson-Schopf Reaction)... 

Recently, Charette et al. have also demonstrated this behavior in the stereoselective cyciopropanations of a number of enantiopure acyclic allylic ethers [47]. The high degree of acyclic stereocontrol in the Simmons-Smith cyclopropanation has been extended to synthesis several times, most notably in the synthesis of small biomolecules. Schollkopf et al. utilized this method in their syntheses of cyclopropane-containing amino acids [48 a, b]. The synthesis of a cyclopropane-containing nucleoside was also preformed using acyclic stereocontrol [48c]. 

An excellent method for the diastereoselective synthesis of substituted amino acids is based on optically active bislactim ethers of cyclodipeptides as Michael donors (Schollkopf method, see Section 1.5.2.4.2.2.4.). Thus, the lithium enolates of bislactim ethers, from amino acids add in a 1,4-fashion to various a,/i-unsaturated esters with high diastereofacial selectivity (syn/anti ratios > 99.3 0.7-99.5 0.5). For example, the enolate of the lactim ether derivative 6, prepared from (S)-valine and glycine, adds in a highly stereoselective manner to methyl ( )-3-phenyl-propenoate a cis/trans ratio of 99.6 0.4 and a syn/anti ratio of 91 9, with respect to the two new stereogenic centers, in the product 7 are found105, los. 

Schollkopf, U. Enantioselective Synthesis of Nonproteinogenic Amino Acids. 109, 65-84 (1983). 

Schollkopf, U. Enantioselective Synthesis of Nonproteinogenic Amino Acids. 109, 65-84 (1983). Shibata, M. Modern Syntheses of Cobalt(III) Complexes. 110, 1-120 (1983). ... 

U. Schollkopf, Asymmetric Synthesis of Amino-Acids, Chem. Scr. 25, NS 105 (1985). 

This section deals mainly with the metalation of lactim ethers and subsequent reaction with electrophiles to generate new C—C bonds at position 3 or 6. Hydrolysis of the products leads to new amino acid esters. The chief attraction of this synthetic route is the high degree of stereoselectivity in the carbon—carbon bond-forming step. It is known as the Schollkopf method for the chiral synthesis of amino acids. 

Schollkopf-Hartwig bislactim ether reagent for asymmetric synthesis of amino acids by reaction of the metalated reagent with... 

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