Lewis acid-catalyzed oxidative

Lewis acid catalyzed oxidations.2 Oxidations with C6H5I02 alone generally proceed rather slowly at room temperature, but are strongly catalyzed by various l.cwis acids. Thus, in the presence of acetic acid, benzylic alcohols are oxidized to aldehydes a-naphthol can be oxidized to theo-quinone under these conditions. Glycol cleavage occurs efficiently with trichloroacetic acid catalysis. 

In the synthesis of graphene-type molecules, dendritic or hyperbranched polyphenylene precursors are transformed into the target molecules through intramolecular cyciodehydrogenation, with concurrent planarization. In this chapter, the various cyciodehydrogenation protocols employed to achieve C-C bond formation will be discussed with respect to their chemistry and applicability towards the construction of graphene-type systems. These transformations include (i) Lewis acid-catalyzed oxidative cyciodehydrogenation (Scholl reaction)... 

Lewis Acid-Catalyzed Oxidative Cyciodehydrogenation (Scholl Reaction)... 

Lewis Acid-Catalyzed Oxidative CYclodehYdrogenation (Schott Reaction) 389... 

Recent attempts to apply cerium(III) chloride (hydrate) and lanthanum(III) acetate to the Lewis acid-catalyzed oxidation of phenols with hydrogen peroxide proved futile in fact, they provided the worst results of over 20 metal salts studied (Ito et al., 1983). Ruthenium trichloride was even better than boron triiluoride, presumably activating the peroxide molecule rather than serving as a one-electron oxidant. 

Zr compounds are also useful as Lewis acids for oxidation and reduction reactions. Cp2ZrH2 or Cp2Zr(0 Pr)2 catalyze the Meerwein-Ponndorf-Verley-type reduction and Oppenauer-type oxidation simultaneously in the presence of an allylic alcohol and benzaldehyde (Scheme 40).170 Zr(C)1 Bu)4 in the presence of excess l-(4-dimethylaminophenyl) ethanol is also an effective catalyst for the Meerwein-Ponndorf-Verley-type reduction.1 1 Similarly, Zr(0R)4 catalyze Oppenauer-type oxidation from benzylic alcohols to aldehydes or ketones in the presence of hydroperoxide.172,173... 

Finally in 2005, Hutt and Mander reported their strategy for the synthesis of nominine (Scheme 1.3) [29], The approach relies upon construction of the steroidal ABC carbocyclic ring structure followed by stepwise preparation of the fused aza-ring system. In the key sequence of the synthetic study, enone 50 was oxidized to dienone 51 with DDQ followed by Lewis acid-catalyzed intramolecular conjugate addition of the methylcarbamate to the newly formed dienone to deliver pyrrolidine 52. 

Adolfsson, H. Mobrg, C. (1995) Chiral Lewis acid catalyzed asymmetric nucleophilic ring opening of cyclohexene oxide., Tetrahedron Asymmetry, 6 2023-2031. 

Pattenden and Teague have prepared tricyclic diol 684 which is epimeric to the naturally occurring A < -capnellene-8p,10a-diol (68S) Their strategy, which is summarized in Scheme LXXI, encompasses two critical cyclization steps. The first is the Lewis acid-catalyzed ring closure of enol acetate 686 and the second involves reductive closure of acetylenic ketone 687. It is of interest that the oxidation of 688 proved to be stereospecific. 

In another research laboratory, surprised by the lack of success of other research groups and the previous statements about the impossibility of applying biocatalytic chemistry to polithiophenes and polypyrroles, special attention was paid to the enzymatic polymerization of the EDOT monomer [43]. In this case, the first trials succeeded and a blue-colored polymer solution was obtained after 16h of reaction (Scheme 4). As is well-known, an acidic reaction medium is suitable to increase the rate of polymerization. Protonic acids and a variety of Lewis acids catalyze the equilibrium reaction of EDOT to the corresponding dimeric and trimeric compounds without further oxidation or reaction [44]. In this work, three different pHs were evaluated (pH = 2, 4, and 6) in order to establish the optimum for adequate synthesis of EDOT. The UV-visible (UV-Vis) spectra for these three reactions are... 

This chapter deals mainly with the 1,3-dipolar cycloaddition reactions of three 1,3-dipoles azomethine ylides, nitrile oxides, and nitrones. These three have been relatively well investigated, and examples of external reagent-mediated stereocontrolled cycloadditions of other 1,3-dipoles are quite limited. Both nitrile oxides and nitrones are 1,3-dipoles whose cycloaddition reactions with alkene dipolarophiles produce 2-isoxazolines and isoxazolidines, their dihydro derivatives. These two heterocycles have long been used as intermediates in a variety of synthetic applications because their rich functionality. When subjected to reductive cleavage of the N—O bonds of these heterocycles, for example, important building blocks such as p-hydroxy ketones (aldols), a,p-unsaturated ketones, y-amino alcohols, and so on are produced (7-12). Stereocontrolled and/or enantiocontrolled cycloadditions of nitrones are the most widely developed (6,13). Examples of enantioselective Lewis acid catalyzed 1,3-dipolar cycloadditions are summarized by J0rgensen in Chapter 12 of this book, and will not be discussed further here. 

Campholenic Aldehyde Manufacture. Campholenic aldehyde is readily obtained by the Lewis-acid-catalyzed rearrangement of a-pinene oxide. It has become an important intermediate for the synthesis of a wide range of sandalwood fragrance compounds. Epoxidation of (+)- Ct-pinene (8) also gives the (+)-o -a-pinene epoxide [1686-14-2] (80) and rearrangement with zinc bromide is highly stereospecific and gives (-)-campholenic aldehyde... 

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