Aryl-de-hydrogenation

As shown in Schemes 10-44 and 10-45, two products may be formed in a Meerwein reaction Scheme 10-44 shows a simple aryl-de-hydrogenation of cinnamic aldehyde, whereas Scheme 10-45 shows an aryl-de-hydrogenation combined with the addition of HC1 to the double bond of the methyl ester of cinnamic acid. No systematic studies have been made as to which of the two products will be formed in a given reaction, what experimental conditions will favor one or the other product, and what substituents or other structural characteristics of the alkene influence the ratio of the two types of product. The addition product can, in most cases, easily be converted... 

Arylation of Aromatic Compounds by Diazonium Salts Arylation or Aryl-de-hydrogenation... 

Two further notes (1) Many transformations can be named using either of two reactants as the substrate. For example, the transformation methylene-de-oxo-bisubstitution above, can also be named ethylidene-de-triphenylphosphoranediyl-bisubstitution. In this book, unless otherwise noted, we will show only those names in which the substrate is considered to undergo the reactions indicated by the titles of the chapters. Thus the name we give to 1-12 (ArH + RCI- ArFt) is alkyl-de-hydrogenation, not aryl-de-chlorination, though the latter name is also perfectly acceptable under the IUPAC system. (2) The IUPAC rules recognize that some transformations are too complex to be easily fitted into the system, so they also include a list of names for some complex transformations, which are IUPAC approved, but nonsystematic (for some examples, see reactions 2-44, 8-36, 9-63). 

Friedel-Crafts Arylation. The Scholl Reaction De-hydrogen-coupling... 

For benzylamine (entry 8) the arylation reaction with m-trifluoromethylbenzene remains the main process (yield 46 %). The only other fluorinated product observed, but the starting compound, is the trifluoromethylbenzene (29 %). In a parallel way, the arylation reaction is apparently accompanied by a partial amine dehydrogenation into the corresponding imine 1, whose formation could explain the presence of N-benzylidene benzylamine 2, and dibenzylamine 2, this last one being detected in small amount. These results are described in the Scheme 1 in which the nickel complex could act as a catalyst for the (de)-hydrogenation processes (refs. 10, 11). 

However, still with p-chlorotrifluoromethylbenzene and the same nickel catalyst, benzylamine gives only the reduction product (entry 10) in the competition between arylation and (de)-hydrogenation process, the last one overbalance owing to the less efficient arylating agent. 

Boc-protection needed during reductive hydrogenation of the azide group to prevent reaction medium becoming basic Competitive de-chlorination of the aryl chloride group occurs under basic conditions... 

It was postulated [152, 153] that the aryl amine is oxidized by direct oxygen transfer from Compound I to the substrate. In contrast, for the oxidation of alkaloids, e.g. morphine, codeine and thebaine (Eq. 12), to the corresponding N-oxi-des by hydrogen peroxide in the presence of HRP or crude enzyme preparation from poppy seedlings, a radical mechanism was proposed [154]. 

Transformation of a phosphonio-substituted phospholide derivative under conservation of the r-electron system has been demonstrated in a number of cases which include substitution of a ring-hydrogen atom, replacement of a PRs -moiety by a hydride, or reductive de-arylation of a PhsP " - to a phosphinyl substituent PPh2. Subsequent re-quaternisation of the latter allows the formal substitution of a PhsP " - by a modified Ph2(R)P -moiety in a two-step reaction. The application of this scheme is not only perfectly suitable for the synthesis of bis-phosphonio-benzophospholides with different phosphonio-moieties but, since the last reaction stage tolerates a variety of functional groups in the electrophile, offers as well a convenient pathway for the synthesis of side-chain functionalised phosphonio-phospholide derivatives from more simple substituted precursors. 

Arylation at a Carbon Containing Active Hydrogen Bis(ethoxycarbonyl)methyl-de-halogenation, etc. 

A pyrrolidine-thiourea organocatalyst (69) facilitates Michael addition of cyclohexanone to both aryl and alkyl nitroalkenes with up to 98% de and ee 202 The bifunctional catalyst (69) can doubly hydrogen bond to the nitro group, leaving the chiral heterocycles positioned for cyclohexyl enamine formation over one face of the alkene. 

The structure of the rearranged methoxy-phenol 27 was easily determined by de-methylation with hydrogen iodide to give the hydroquinol 30. Oxidation affords the red 2,3,4,6-tetraphenylquinone 31, identical to the quinone which was first prepared by Kvalnes, 6> by arylating quinone with aryldiazonium salts. 

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