Semicorrins, synthesis

Semicorrins, synthesis 26, 796 Sensitizers (s. a. Triplet sensitizers) acetone 26,720 acetophenone 26, 763 N,N-dimethylaniline 26, 85 fluorenone 22, 761 suppl. 26 methylene blue 26, 125 xylene 26, 135, 146 Sequestering agent s. Sodium pyrophosphate Shift b. a. Migration,... 

Semicorrin ligands have also been used in asymmetric cyclopropanation of silyl enol ethers to give optically active silyloxycyclopropanes which, after acid-catalyzed ring opening, serve as convenient precursors in the synthesis of chiral y-oxo carboxylic esters50. 

Ibesc ligands are generally prepared from D- or i.- pyroglutamic acid. An attractive short synthesis is shown in equation I. Several 5 aza-semicorrins such as 1 arc known and... 

There is another system, that of BINOL/BINAP, the Japanese dream of a universal chiral auxiliary [88], and there are striking similarities, but also fundamental differences, when compared with the TADDOLs (see Scheme 16). There is still a lot to do, and there are other competitors out there, sometimes referred to as preferred ligands (such as the semicorrine and oxazoline [89], the metallocene [90], the diaminocyclohexane [91], and the quinine/cincho-nine [92] systems). Everybody in the field of EPC synthesis dreams of hav-... 

Cor mth stereoselective olefin synthesis 14,717 Corrins s. Semicorrins Conmarans... 

Semicorrins have been previously prepared as intermediates in the synthesis of corrinoid and hydroporphinoid compounds [12,13]. The classic route by iminoester-enamine condensation, devisal by Eschenmoser [12], is ideally suited for preparing chiral C2-symmetric semicorrins 1 (Scheme 1). Starting either from L-pyroglutamic acid (-)-3 or from the D-enantiomer, which are both commercially available at moderate prices, the crystalline, enantiomerically pure (S,Sy and (/ ,/ )-diesters (-)-la and (+)-la are readily synthesized in multigram quantities with an overall yield of 30-40 % (Scheme 2) [8,14]. The diesters can be converted to a variety of differently substituted semicorrins by selective trans-... 

Thanks to the fundamental studies of Tsuji, Trost, and others, palladium-catalyzed allylic substitution has become a versatile, widely used process in organic synthesis [40]. The search for efficient enantioselective catalysts for this class of reactions is an important goal of current research in this field [41]. It has been shown that chiral phosphine ligands can induce substantial enantiomeric excesses in Pd-catalyzed reactions of racemic or achiral allylic substrates with nucleophiles [42]. Recently, promising results have also been obtained with chiral bidentate nitrogen ligands [43]. We have found that palladium complexes of neutral aza-semicorrin or methylene-bis(oxazoline) ligands are effective catalysts for the enantioselective allylic alkylation of l,3-diphenyl-2-propenyl acetate or related substrates with dimethyl malonate (Schemes 18 [25,30] and 19 [44]). 

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