Semicorrin structure

Chiral C2-symmetric semicorrins (structure 4), developed by Pfaltz [11], were proven to be highly efficient ligands for the copper-catalyzed enantio-selective cyclopropanation of olefins. Variations of the substituents at the stereogenic centers led to optimized structures and very high enantioselectiv-ities [12]. 

Subsequently, bis(oxazoline) ligands ((70) and (71)), structurally related to the semicorrin ligand, were introduced and further expanded the scope of asymmetric cyclopropanation... 

Figure 3. X-ray crystal structure of Pfaltz semicorrin-copper catalyst (40). [Adapted from (31).]...

Pyrrolidinyl Enolate-, and Semicorrinate Anions as Chelate Ligands for fron(II) and Copper(II) Ions From Molecular to Collective Structures. 152... 

Semicorrins form stable chelate complexes with a variety of metal ions such as Co , Rh Pd , or Cu . Depending on the metal ion, the ligand structure, and the reaction conditions, mono-or bis(semicorrinato) complexes are obtained. - ... 

In close structural analogy to the semicorrinate ligands of 9, the bidendate, chiral C2-symmetric 5-azasemicorrins 10 and bis(4,5-dihydrooxazol-2-yl)methane systems n is6,2i7 12 218,219 12 a, and 14 perform exceptionally well in copper-catalyzed enantioselective cyclo-... 

In close structural analogy to the semicorrinate ligands of 9, the bidendate, chiral C2-symmetric 5-azasemicorrins 10216 and bis(4,5-dihydrooxazol-2-yl)methane systems li,196 217 12,218 219 12a,197 13,220 and I4197a perform exceptionally well in copper-catalyzed enantioselective cyclo-propanation reactions with diazo esters. With 10, 11, and 12 a, the active catalyst is prepared in situ by adding a catalytic amount of a copper(I) salt with a weakly coordinating anion [copper(I) triflate,196,217,219 copper(I) perchlorate197] to the free ligand with the enolizable system 12 (as well as with 12a and 14) it has been prepared by reaction with copper(I) terh butoxide or from the copper(I) bischelate complex by reduction with phenylhydrazine. 

Intramolecular cyclopropanations with unsaturated diazo ketones have also been reported. Furthermore, enantioselective cyclopropanation with diazomethane can be achieved in up to 75% ee. In detailed mechanistic discussions, a copper(I) species, complexed with only one semicorrin ligand, and formed by reduction and decomplcxation, is suggested as the catalytical-ly active species, cisjtrans Stereoselection and discrimination of enantiotopic alkene faces should take place within a copper-carbene-alkene complex25-54"56. According to these interpretations, cisjtrans selectivity is determined solely by the substituents of the alkene and of the diazo compound (especially the ester group in diazoacetates) and is independent of the chiral ligand structure (salicylaldimine or semicorrin)25. 

Jacobi and Liu used the Dinu-oth rearrangement to generate structural motifs for semicorrins, tripyrrolines, and higher analogs such as cobyric acid, a functional analog of vitamin B12. Treatment of iminolactone... 

Inspired by the structures of corrinoid and porphinoid metal complexes, which in nature play a fundamental role as biocatalysts, we have developed a route to chiral C2-symmetric semicorrins 1, a class of bidentate nitrogen ligands specifically designed for enantioselective catalysis [7]. These ligands possess a number of structural features that make them attractive ligands for the stereocontrol of metal-catalyzed reactions. 

The obvious first test of methylene-bis(oxazolines) 6 was the copper-catalyzed cyclopropanation. Among the various derivatives that we had prepared (6 R = benzyl, c-alkyl, phenyl, tert-hutyl the bulky t rt-butyl-substituted derivative proved to be the most effective ligand, giving similarly high enantiomeric excesses as the semicorrin Ic (R = CMe20H) (Scheme 14) [25]. The same results were obtained by Masamune and coworkers in an independent parallel study [28]. More recently, Lowenthal and Masamune showed that the method works also well for certain trisubstituted and unsymmetrically disubstituted cis-olefins if the di-t rt-butyl-substituted ligand is replaced by structurally modified bis(oxazolines) [32]. 

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