Best Synthetic Methods Oxidation

Although the enantioselective oxidation of alkyl aryl sulfides is well developed, much less is known about dialkyl sulfides. Tsutomu Katsuki of Kyushu University has designed J. Am. Chem. Soc. 2007, 129, 8940) an Fe(salan) complex that combines with aqueous to oxidize alkyl methyl sulfides in high ee. 

The oxidation of alcohols to aldehydes and ketones is one of the most widely practiced of synthetic transformations. Ge Wang of the University of Science and Technology in Beijing has developed Chem. Lett. 2007, 36, 1236) a Mo catalyst that used aqueous to effect this transformation. Secondary alcohols are oxidized more rapidly than primary alcohols. Vinod K. Singh of the Indian Institute of Technology, Kanpur, has found Synth. Comm. 2007, 37, 4099) that the solid, inexpensive 6 can take the place of oxalyl chloride in the Swem oxidation. Viktor V. Zhdankin of the University of Miimesota, Duluth has devised J. Org. Chem. 2007, 72, 8149) a polymer-bound hypervalent iodine reagent that is easily separated after use, and reoxidized for reuse. 

Enones such as 11 are versatile intermediates for organic synthesis. Makoto Tokunaga, now at Kyushn University, and Yasushi Tsnji, now at Kyoto University, have fotmd Tetrahedron Lett. 2007, 48, 6860) a Pd catalyst that, in the presence of O, will oxidize a cycUc ketone snch as 10 to the enone. 

The direct oxidation of an alcohol to the acid is not always an efficient process, so the conversion of 12 to 13 would often be carried out over at least three steps. David Milstein of the Weizmann Institute of Science has devised Science 2007, 317, 790) a Ru catalyst that effected the transformation in a single step, generating as a byproduct as the oxida- 

The oxidation of an aldehyde to the corresponding amide is also a useful transformation. Noritaka Mizuno of the University of Tokyo has designed (Angew. Chem. Int. Ed. 2007, 46, 5202) a Rh catalyst that can combine, in water, the aldehyde 14 and NH OH to give the primary amide 15. Johann Chan of Amgen Inc., Thousand Oaks, CA has found J. Am. Chem. Soc. 2007,129, 14106) a different Rh catalyst that mediated the oxidation of a sulfonamide to the nitrene, which under the reaction conditions inserted into the aldehyde H to give the amide 17. 

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Best Synthetic Methods Enantioselective Oxidation and Reduction... 

A. H, Haines, Methods for the Oxidation of Organic Compounds Alcohols, Alcohol Deriatives, Alkyl Halides, Nitroalkanes, Alkyl Azides, Carbonyl Compounds, Hydroxyarenes, and Aminoarenes , in the series Best Synthetic Methods , ed. A. R. Katritzky, O. Meth-Cohn and C. W. Rees, Academic Press, New York,... 

A.H. Haines, Best Synthetic Methods - Methods for the Oxidation of Organic Compounds Alkanes, Alkenes, Alkynes and Arenes, Academic Press, London and Orlando FL, 1985. 

Terminal double bonds are selectively oxidized to methyl ketones. A typical procedure for the oxidation of 1-decene to 2-decanone in 65-73% yield with PdCli/CuCl is given in Organic SynthesisAlthough there are several known synthetic methods for methyl ketone preparation, the PdCh-catalyzed oxidation of terminal alkenes seems to be one of the best. In other words, terminal alkenes can be regarded as precursors of methyl ketones, or as masked methyl ketones based on this reaction. This re-... 

The first reports of a reaction of an amine with an aldehyde by Schiff [584] led to the establishment of a large class of ligands called Schiff bases. Among the most important of the Schiff bases are the tetradentate salen ligands (N,N -bis(salicy-laldehydo)ethylenediamine), which were studied extensively by Kochi and coworkers, who observed their high potential in chemoselective catalytic epoxidation reactions [585]. The best known method to epoxidize unfunctionalized olefins enantioselectively is the Jacobsen-Katsuki epoxidation reported independently by these researchers in 1990 [220,221]. In this method [515,586-589], optically active Mn salen) compounds are used as catalysts, with usually PhlO or NaOCl as the terminal oxygen sources, and with a O=Mn (salen) species as the active [590,591] oxidant [586-594]. Despite the undisputed synthetic value of this method, the mechanism by which the reaction occurs is still the subject of considerable research [514,586,591]. The subject has been covered in a recent extensive review [595], which also discusses the less-studied Cr (salen) complexes, which can display different, and thus useful selectivity [596]. Computational and H NMR studies have related observed epoxide enantioselectivities... 

This method of preparation of ylides from the corresponding triazolinedi-ones is limited in its synthetic utility. Oxidation of suitable urazolyl compounds seems to be a much more versatile entry to this class of highly reactive dipolar compounds. Starting substituted urazoles are often readily available by simple nucleophilic substitution reactions of urazoles with suitable alkyl halides. As is evident from the preceding sections, many other substituted urazoles can be prepared by the ene-type reaction of TADs, by the reaction of TADs with ketones, or by their electrophilic aromatic substitution reactions. Oxidation of these urazoles, e.g., 501, 428, 504, and 506, can be effected with tert-butyl hypochlorite, or, in some cases, excess PTAD can be used. Various approaches and utilization of this synthetic strategy are best seen in the following examples. 

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