Alkoxy groups elimination

In the effort to make pure blue-emitting materials Shim and coworkers [146] synthesized a series of PPV-based copolymers containing carbazole (polymers 95 and 96) and fluorene (polymers 97 and 98) units via Wittig polycondensation. The use of trimethylsilyl substituents, instead of alkoxy groups, eliminates the electron donor influence of the latter and leads to chain distortion that bathochromically shifts the emission (Amax = 480 nm for 95 and 495 nm for 97). In addition, a very high PLQY was found for these polymers in the solid state (64 and 81%, respectively). Single-layer PLEDs fabricated with 95 and 97 (ITO/polymer/Al) showed EL efficiencies of 13 and 32 times higher than MEH-PPV, respectively (see also Ref. [147] for synthesis and PLED studies of polymers 99 and 100) (Chart 2.20). 

In all cases examined the ( )-isomers of the allylic alcohols reacted satisfactorily in the asymmetric epoxidation step, whereas the epoxidations of the (Z)-isomers were intolerably slow or nonstereoselective. The eryfhro-isomers obtained from the ( )-allylic alcohols may, however, be epimerized in 95% yield to the more stable tlireo-isomers by treatment of the acetonides with potassium carbonate (6a). The competitive -elimination is suppressed by the acetonide protecting group because it maintains orthogonality between the enolate 7i-system and the 8-alkoxy group (cf the Baldwin rules, p. 316). 

IV-Methylated pyridazinones can be obtained from 3,6-dialkoxypyridazines by treatment with alkyl halides or dialkyl sulfates. Methyl iodide and dimethyl sulfate are most frequently used. According to the proposed mechanism, an intermediate quaternary pyridazinium salt is formed, followed by elimination of a group R from the alkoxy group. At higher temperature, l,2-dimethylpyridazine-3,6(l//,2//)-dione is formed with dimethyl sulfate. 

Photolysis of derivatives of compounds 4 and 5 has been further studied as a route to azacarbazoles. The example 264 shows normal behavior as well as elimination of an alkoxy group, and the report includes examples of derivatives of compound 5 as well as references to earlier work (93JCS(P1)1261). Production of an intermediate for an anti-tumour ellipticine analogue is shown by example 265 (84MI1), and incorporation of acetonitrile solvent by example 266 (91TL323). 

These A -acyl phosphazenes also decompose further on heating to PhaMePO and RCN. The elimination of methyl iodide probably occurs by a course closely related to the elimination of alkyl halides in the Arbusov reaction, where the alkoxy-group undergoes nucleophilic attack by halide ion. 

Aldehydes can be obtained by reaction of Grignard reagents with triethyl orthoformate. The addition step is preceded by elimination of one of the alkoxy groups to generate an electrophilic oxonium ion. The elimination is promoted by the magnesium ion acting as a Lewis acid.93 The acetals formed by the addition are stable to the reaction conditions, but are hydrolyzed to aldehydes by aqueous acid. 

Elimination of an alkoxy group or of a halogen in the case of zirconacyclopentenes has been investigated in combination with the (3, (3-carbon—carbon bond-cleavage reaction. As shown in Eq. 2.73, an OR group or a halogen at a (3-position is eliminated and trapped by the zirconium metal center [53],... 

Ti-mediated cyclization of an allenynes having a leaving group provides a five-membered ring with cross-conjugated trienes which might be produced by the elimination of an alkoxy group from a titanacycle (Scheme 16.73) [79]. 

Elimination of a Halogen and a Hetero Group Alkoxy-halo-elimination... 

Our interest in silane coupling agents and in the preparation of silicates has led us to study the mechanisms involved in the various reactions. In a previous paper, we investigated the kinetics and mechanism of the alcoholysis of TMOS [13]. This present work studies the effects of changing the substituents on a para-substituted phenyl attached directly to the alkoxysilane. The alkoxysilane silanes used have only one alkoxy group present to eliminate complications from a competing second or third alcoholysis reaction. The resulting Hammett plot yields additional information on the mechanism of this reaction. 

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