Synthesis elimination reactions

Alkenes and Alkynes I Properties and Synthesis. Elimination Reactions of Alkyl Halides 291... 

PROPERTIES AND SYNTHESIS. ELIMINATION REACTIONS OF ALKYL HALIDES 291... 

Synthesis. The first hiUy alkyl/aryl-substituted polymers were reported in 1980 via a condensation—polymeri2ation route. The method involves, first, the synthesis of organophosphine-containing alkyl or aryl substituents, followed by the ready oxidation of the phosphine to a phosphorane with leaving groups suitable for a 1,2-elimination reaction. This phosphorane is then thermally condensed to polymers in which all phosphoms atoms bear alkyl or aryl substituents. This condensation synthesis is depicted in Eigure 2 (5—7,64). 

The amino functional group is not commonly encountered in steroid synthesis except perhaps in steroidal alkaloids. However, certain elimination reactions have been shown to have theoretical and limited preparative importance, largely due to the efforts of McKenna and co-workers. The Hofmann rule for 2 elimination predicts that alkaline elimination of quaternary ammonium salts will occur towards the carbon carrying the most hydrogen atoms cf. the converse Saytzeff orientation, above). In cyclohexyl systems, the requirement for diaxial elimination appears to be important, as in other 2 eliminations, and the Hofmann rule frequently is not obeyed [e.g., (116) (117)]. 

The final variation of the Feist-Benary furan synthesis encompasses reactions of 1,3-dicarbonyls with 1,2-dibromoethyl acetate (52). For example, treatment of ethyl acetoacetate (9) with sodium hydride followed by addition of 52 at 50°C yields dihydrofuran 53. The product can be easily converted into the corresponding 2-methyl-3-furoate upon acid catalyzed elimination of the acetate, thus providing another strategy for the synthesis of 2,3-disubstituted furans. 

Except for terpene chemistry, the Wagner-Meerwein rearrangement is of limited synthetic importance. It is rather found as an undesired side-reaction with other reactions, for example in the synthesis of alkenes by elimination reactions. 

Progressive departure from the fundamental structure of the lead agent cimetidine led to the anti ulcer agent oxmetidine (47). The synthesis involves -methylation (CH3I) of the 2-thiouracil intermediate and is followed by an addition-elimination reaction with 2-(5-methyl-4-imidazolylmethylthio) ethylamine to give oxmetidine (47). ... 

Hexamethylphosphoramide Hoffmann, Roald, 1180 Hoffmann-I.a Roche Co., vitamin C synthesis and, 773 von Hofmann. August Wilhelm, 933 Hofmann elimination reaction. 936-938... 

The preparation of mono- and di-tm-butylcyclopentadienes 1 and 2 starting from monomeric cyclopentadiene was reported first in 1963 [23]. It was noted that the nucleophilic attack of the cyclopentadienide anion on ferf-alkyl halide has to compete with elimination reaction giving isobutene. The yield of the di- and tri-fer/-butylcyclopentadienes 2 and 3 was therefore reported to be modest to low [23, 24], Recently an elegant improvement for this synthesis using phase transfer catalysis was presented (Eq. 1), but the availability of the tri-substituted derivative... 

The solid-phase synthesis of the 2(lff)-pyrazinone scaffold is based on a Strecker reaction of commercially available Wang amide linker with appropriate aldehyde and tetramethylsilyl (TMS) cyanide, followed by cyclization of a-aminonitrile with oxalyl chloride resulting in the resin linked pyrazinones. This approach allows a wide diversity at the C-6-position of pyrazinone scaffold (Scheme 35, Table 1). As it has been shown for the solution phase, the sensitive imidoyl chloride moiety can easily undergo an addition/elimination reaction with in situ-generated sodium methoxide affording the resin-linked... 

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