Asymmetric alkene

Molybdenum catalysts that contain enantiomerically pure diolates are prime targets for asymmetric RCM (ARCM). Enantiomerically pure molybdenum catalysts have been prepared that contain a tartrate-based diolate [86], a binaph-tholate [87], or a diolate derived from a traris-1,2-disubstituted cyclopentane [89, 90], as mentioned in an earlier section. A catalyst that contains the diolate derived from a traris-1,2-disubstituted cyclopentane has been employed in an attempt to form cyclic alkenes asymmetrically via kinetic resolution (inter alia) of substrates A and B (Eqs. 45,46) where OR is acetate or a siloxide [89,90]. Reactions taken to -50% consumption yielded unreacted substrate that had an ee between 20% and 40%. When A (OR=acetate) was taken to 90% conversion, the ee of residual A was 84%. The relatively low enantioselectivity might be ascribed to the slow interconversion of syn and anti rotamers of the intermediates or to the relatively floppy nature of the diolate that forms a pseudo nine-membered ring containing the metal. 

A more versatile method to use organic polymers in enantioselective catalysis is to employ these as catalytic supports for chiral ligands. This approach has been primarily applied in reactions as asymmetric hydrogenation of prochiral alkenes, asymmetric reduction of ketone and 1,2-additions to carbonyl groups. Later work has included additional studies dealing with Lewis acid-catalyzed Diels-Alder reactions, asymmetric epoxidation, and asymmetric dihydroxylation reactions. Enantioselective catalysis using polymer-supported catalysts is covered rather recently in a review by Bergbreiter [257],... 

Like alkenes, asymmetrical alkynes follow Markovnikov s rule when an asymmetrical molecule, such as H2O or HBr, is added to the triple bond. An example is given below. 

Keywords Alcohols Alkenes Asymmetric transfer hydrogenation C-alkylation Imines Ketones W-aUcylation Oxidation Reduction Transfer hydrogenation... 

Functionalized Alkenes Asymmetric hydroformylation of functionalized alkenes can serve as a useful method for the syntheses of polyfunctionalized intermediates to biologically... 

Alkyl-substituted acyclic alkenes, asymmetric hydrosilylation,... 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

Scheme 13. [2 + 2] Photocycloaddition of enones with alkenes Asymmetric induction by chiral centers of the alkenes.

The epoxide functional group is often an intermediate in organic synthesis sequences because it can be readily opened by a variety of nucleophiles, leading to complex functionalization that starts with just an alkene. Asymmetric variants of epoxidation are important reactions, with the Sharpless and Jacobsen epoxidations being the most well known. Both these reactions involve metal catalysts. 

The past 30 years have witnessed an explosion of oxo knowledge such as the conversion of unfunctionahzed alkenes asymmetric, tandem, or sequential reactions and the work in other and unconventional media with highly sophisticated... 

Regioselective hydroamidation of 1-alkynylphosphine sulfides provided (E)-2-amino-l-thiophosphinyl-l-alkenes. Asymmetric hydrogenation led to the corresponding saturated derivative (Scheme 25). ... 

Huang XG, Craita C, Vogel P. Palladium-catalyzed conversion of (3,7-unsaturated silyl suliinates into (E)-alkenes asymmetric synthesis of polypropionate fragments. J. Org. Chem. 2004 69(12) 4272 275. 

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