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Vincent Lopez
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Directed ortho metalation
Directed ortho metallation (DOM) is an adaptation of electrophilic aromatic substitution in which only bind electrophiles to the ortho-position of a group DMG direct metallation or through a compound aryllithium. The DMG interacts with lithium through a hetero. DMG Examples are the methoxy group, a tertiary amino group and an amide group.
The general principle is described in Schedule 1. An aromatic ring system with a DMG group interacts with an alkyllithium such as n-butyl-lithium in your specific aggregation state (hence (R-Li) n) from the middle two heteroatom in the DMG is a Lewis base and Lewis acid lithium. The very basic alkyllithium then deprotonated ring at the nearest position to form the ortho-aryllithium 3 while maintaining the interaction acid-base. An electrophile reacts in the next phase electrophilic aromatic substitution with a strong preference for the position of replacing the lithium ipso lithium atom.
Ordinary electrophilic substitutions with a preference group showed activation for both the ortho and para position, this reaction shows regioselectivity increased because the ortho is the only objective.
This type of reaction was discovered independently by Henry Gilman and Georg Wittig around 1940.
Scope
Victor Snieckus, one of the most active researchers studying ortho lithiation
DOM has been applied to the synthesis of enantiopure benzyl amines in scheme 3. When you reach the intermediate lithium bulky tosyl group on the imine electrophile is responsible for conducting asymmetric induction.
In another DOM implementation applies to the placement of a bulky tert-butyl group in ortho position (Scheme 4). The lithiation is an aromatic nucleophilic substitution and subsequent reaction to an electrophilic aromatic substitution sulfoxide. In the acts of tert butyllithium final step as a nucleophile in aromatic substitution nucleophilic addition through an anionic intermediate.
Directed metallation is not limited to lithium intermediates or even a rising preference. In a study found that the product of the reaction of N, N-dimethylaniline with a complex of TMEDA, sodium salt of TMP and di-tert-butylzinc is a meta zinc complex as a crystalline compound stable. This complex reacts with iodine electrophile N, N-dimethyl-3-iodoaniline:
DoM has also been applied in combination with a Suzuki in a synthesis reaction one-pot:
References
^ Directed ortho metalation. Tertiary amide and O-carbamate directors in synthetic strategies for polysubstituted aromatic Victor Snieckus Chem Rev., 1990, 90 (6), 879-933. Summary
^ Relative reactivities of organometallic compounds. XX .* metallation Henry Gilman, Robert JL Am Bebb Chem Soc, 1939, 61 (1), 109-112. Summary
^ G. Wittig et al. Chem Ber. 1940, 73, 1197
^ Ortho-metallation of enantiopure aromatic Sulfoxides and Stereocontrolled Addition to Imines Nicolas Le Fur, Ljubica Mojovic, Nelly Pl, Alain Turck, Vincent Reboul and Patrick Metzner J. Org. Chem, 2006, 71 (7), pp 2609-2616; Summary
^ Scheme 3. reaction scheme: the reaction of iodobenzene with n-butyl lithium (S)-tert-butyl-tert butanethiosulfinate enantiopure sulfoxide followed by a reaction DOM re-initiated by n-butyl lithium N-tosylimine electrophilic. The sulfoxide group is removed by hydrogenation with Raney nickel. Ts is a tosyl group, is ee enantiomeric excess
^ Anti-tert-Friedelrafts butylation substituted aromatic rings via directed metallation and sulfinylation Jonathan Clayden, Christopher C. Stimson and Martine Keenan Chemical Communications, 2006, 1393-1394 Summary
^ Directed metallation Using meta-alkali-Metal-Mediated Zincation David R. Armstrong, William Clegg, Sophie H. Dale, Eva Hevia, Lorna M. Hogg, Gordon W. Honeyman, Robert E. Mulvey Angewandte Chemie International Edition Volume 45, Number 23, pages 3775-3778 2006 doi: 10.1002/anie.200600720
^ A reaction) hexane solvent at room temperature. Selected bond lengths in 2: Zn-C bonds 203.5 hours in plane with the plane aryl, Na-C bonds 269 hours by plane from 76 to aryl
^ Directed ortho-metalation and Suzuki-Miyaura Boronation Cross Coupling of Pyridine Derivatives: A protocol of a pot Azabiaryls replaced Manlio Alessi, Andrew L. Larkin, Kevin A. Ogilvie, Laine A. Green, Sunny Lai, Simon Lopez, and Victor Snieckus J. Org. Chem, 2007, 72 (5) pp 1588-1594, (Article) DOI: 10.1021/jo0620359
^ In this sequence the starting material is lithiated nicotinamide then reacted with an ester triisopropoxyborane boronate then reacted with pinacol and finally reacted with iodobenzene and tetrakis (triphenylphosphine) palladium (0)
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