Diastereomer derivatives reagent selection

Currently, several hundred reagents are available for the preparation of diastereomer derivatives, and this list continues to grow. In consequence, any type of comprehensive coverage is impossible here. As well as the nature of the reactive group, cost, reactivity, stability, and availability are important selection criteria, since in advance of trial experiments, success cannot be guaranteed for analytes not studied previously. For trace analysis, the choice of a more selective and sensitive detector for the analysis may minimize the number of options to reagents with suitable characteristic detector properties. 

Similar results are found with the threose derivatives 11 and 13. Both aldehydes can be readily synthesized in either enantiomeric form from l- and D-tartaric acid. The open-chain aldehyde 11 with Grignard reagents affords predominantly the all-.v> n(xj/o)-diastereomer 12. The steric demand of the nucleophile apparently does not affect the diastereoselectivity, and the extremely high selectivity observed with [(l,3-dioxolan-2-yl)methyl]magnesium bromide is attributed to the presence of the dioxolane moiety, which is thought to stabilize the a-chelated transition state. 

Addition of Grignard and organolithium reagents to imines 2. derived from enantiomerically pure (S)-valinol (1), provides a-substituted phenethylamines 3 in moderate to good yield and excellent diastereoselectivity (in each case only one diastereomer can be detected by NMR)15. By appropriate selection of imine and organometallic reagent both diastereomeric amines are accessible (see also refs 16 and 17). 

In some cases (3), the addition of a chiral shift reagent (Eu(hfc)3) is necessary to obtain baseline separation of the signals corresponding to the p-proton of both diastereomers by H NMR. Diastereomeric mixtures derived from secondary alcohols have also been analyzed by HPLC. The resolution of a secondary alcohol (4) could be achieved by a selective crystallization of one of the two diastereomeric camphorsulfonate esters. ... 

The reduction of sullinyl imines is well precedented. Recently, Ellman demonstrated that the tcrt-butyl derivative is a highly selective reagent for this transformation that can also be removed under very mild conditions. Formation of the imine using titanium ethoxide followed by reduction under standard conditions (sodium borohydride in methanol) provided the desired product as a 5 1 mixture of diastereomers (Scheme 5.14). 

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