Double inversion of configuration

The vinylogous elimination to give alkenylcyclopropanes may also be effected via rt-allyl palladium complexes34,35. The palladium(0)-catalyzed substitution of allylic esters with stabilized carbon nucleophiles via 7i-allyl palladium derivatives stereospecifically proceeds with net retention (double inversion) of configuration. Thus, the chirality of an allylic substrate is transferred to resultant alkenylcyclopropanes in the intramolecular S J/ reaction via 7i-allyl palladiums (equation 21)36,3. ... 

In this reaction sequence, allylic alcohol 6 is converted into 7 with a double inversion of configuration, and thus retention. 

Alkyl Migration with Double Inversion of Configuration... 

With retaining enzymes, the configurations at the anomeric center of the substrate (glycoside) and the product (free sugar) are the same after two nucleophilic attacks at this carbon, with overall double inversion of configuration (Scheme 9.19). 

The 5 -phosphoramidite of the novel bicyclic nucleoside (14), restricted to an S-type conformation, has been synthesised in eight steps via double inversion of configuration at the C4 position of protected l-(3 -deoxy-p-D-psicofuranosyl)uracyl and introduction of an azide moiety. The secondary amino group at C4 permitted the subsequent incorporation of (14) into oligonucleotides via a 5 -3 directed variation of the standard phosphoramidite approach for synthesis of oligonucleotides. Thermal denaturation studies showed rather large decreases in duplex stabilities toward complementary DNA and RNA. ... 

Synthesis from o-mannose Synthesis of (-)-swainsonine (1) has been also ac-comphshed by utihzing D-mannose as a starting material (Scheme 4).2i8-220 p-Mannose was converted into 42 in 81% overall yield. Double inversion of configuration at C-4 of 42... 

Exposure of 1 to aliphatic expoxides (58) results in the corresponding sulfamidates (59). The sulfamidates can be further converted to cw-amino alcohols (60) with double inversion of configuration.17... 

This mechanism accounts for retention of configuration in both directions without requiring sequential double inversion of configuration. It also provides for a plausible explanation of the essential role of pyridoxal-5 -phosphate in glycogen phosphorylase catalysis, as the phosphate of the cofactor, pyridoxal-5 -... 

The scope of regio- and stereo-selective synthesis of vinylallenes by 1,5-(>S )-substitution of enyne acetates and oxiranes with organocuprates has been explored the products are usually obtained as mixtures of E- and Z-isomers (Scheme 12), ° Optimum conditions for stereoselective alkynylation of trans-2,3-epoxy sulfides at C(2), with double inversion of configuration, on reaction with alkynylaluminiums (Scheme 13) have been sought. 

Fig. 6. Formation of Wl- 4) linkage via substrate enzyme complex involvii double inversion of configuration at Cl catbon...

In this section, we will consider reactions of amino acids other than those leading to peptide formation—that is much the most significant process and will be covered in the next section. Many of the other reactions are simply those you would expect for primary amines, or carboxylic acids. The amino groups can be acylated by acid chlorides or anhydrides (Figure 22.24). Reaction with nitrous acid leads to diazotization the reaction in Figure 22.25 goes with a double inversion of configuration, via an unstable a-lactone. The product is obtained in better than 95 % enantiomer excess. 

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