Editing Stereoselectivity (section)

==Examples==
An example of modest stereoselectivity is the [[dehydrohalogenation]] of 2-iodobutane which yields 60% ''trans''-2-butene and 20% ''cis''-2-butene.<ref>'' Effects of base strength and size upon in base-promoted elimination reactions.'' Richard A. Bartsch, Gerald M. Pruss, Bruce A. Bushaw, Karl E. Wiegers 
[[J. Am. Chem. Soc.]]; '''1973'''; 95(10); 3405-3407. {{doi|10.1021/ja00791a067}}</ref> Since alkene [[geometric isomer]]s are also classified as diastereomers, this reaction would also be called diastereoselective.

:[[File:Stereoselectivedehalogenation.svg|411px|Stereoselective dehalogenation]]

[[Cram's rule]] predicts the major diastereomer resulting from the diastereoselective nucleophilic addition to a carbonyl group next to a chiral center. The chiral center need not be optically pure, as the relative stereochemistry will be the same for both enantiomers. In the example below the (S)-aldehyde reacts with a thiazole to form the (S,S) diastereomer but only a small amount of the  (S,R) diastereomer:<ref>Organic Syntheses, Coll. Vol. 10, p.140 (2004); Vol. 77, p.78 (2000). [http://orgsynth.org/orgsyn/pdfs/V77P0078.pdf Link]</ref>

:[[File:Stereoselectiveadditiontoathiazole.svg|370px|Stereoselective addition of a thiazole to an aldehyde]]
The [[Sharpless epoxidation]] is an example of an enantioselective process, in which an [[Chirality (chemistry)|achiral]] [[allylic alcohol]] substrate is transformed into an optically active epoxyalcohol. In the case of chiral allylic alcohols, kinetic resolution results. Another example is [[Sharpless asymmetric dihydroxylation]]. In the example below the achiral alkene yields only one of the possible 4 stereoisomers.<ref>Organic Syntheses, Coll. Vol. 10, p.603 (2004); Vol. 79, p.93 (2002).[http://orgsynth.org/orgsyn/pdfs/V77P0078.pdf Link]</ref>

:[[File:StereoselectiveSharplessOxidation.svg|309px|Stereoselective Sharpless oxidation]]

With a [[stereogenic]] center next to the carbocation the substitution can be stereoselective in inter- <ref>'' Diastereoselective Friedel-Crafts Cyclization Reactions to 2-Substituted 1-Phenyl-1,2,3,4-tetrahydronaphthalenes'' Friedrich Mühlthau, Thorsten Bach Synthesis '''2005''': 3428-3436 {{doi|10.1055/s-2005-918482}}</ref> and intramolecular <ref>'' High Facial Diastereoselectivity in Intra- and Intermolecular Reactions of Chiral Benzylic Cations'' Friedrich Mühlthau, Oliver Schuster, and Thorsten Bach [[J. Am. Chem. Soc.]], '''2005''', 127 (26), pp 9348–9349 {{doi|10.1021/ja050626v}}</ref><ref>''Stereoselective Reactions with Stabilized Carbocations'' Pier Giorgio Cozzi and Fides Benfatti [[Angew. Chem. Int. Ed.]] '''2009''', 48 {{doi|10.1002/anie.200905235}}</ref> reactions. In the reaction depicted below the nucleophile (furan) can approach the carbocation formed from the least shielded side away from the bulky [[t-butyl]] group resulting in high facial diastereoselectivity:

:[[File:Stereoselectivereactionwithcarbocations.svg|Stereoselective reaction with carbocation Bach 2005]]