Dehydrohalogenation with simultaneous

This strategy has been appHed to different solid-supported dipolarophiles such as alkynes [277] and 3-hromo-4,4,4-trifluorobutenoic acid [278], which gave rise to isoxazoles upon dehydrohalogenation. Solid-supported vinyl ethers (215) [279] are worth mentioning, because TFA treatment of the resulting isoxazolines intermediate afforded isoxazoles (218) with simultaneous release from the resin (Scheme 48). 

Intramolecular condensation of pyrrolidone 32 occurred simultaneously with dehydrohalogenation on treatment with sodium ethoxide, giving the sodium salt, which on acidification yielded the hydroxypyrrolizine (33). No information concerning tautomeric structures 33a,b could be obtained, but a l,7-dihydroxy-3/f-pyrrolizine structure (34) could be excluded.29... 

It seems unlikely that the influence of the metal is of an electrophilic nature, inducing a carbonium-ion mechanism, as the products of substitution and dehydrohalogenation are never found simultaneously. More plausibly the metal donates electrons, and carbanion or concerted processes with carbanion character rather than radical processes are usually favoured. Radical additions occur very easily to olefinic double bonds and l-bromo-l,2-diphenylethane undergoes radical bromination with N-bromosuccinimide without accompanying dehalogenation. ... 

Scheme 6.87. A representation of the reaction between benzene (CgHg) and 1-chloropropane (CH3CH2CH2CI) to produce both 1-phenylpropane and 2-phenylpropane. It is suggested that the former is generated by the reaction of an aluminum trichloride (AICI3) complex with the alkyl halide. Simultaneously, dehydrohalogenation of the halide leads to alkene that, in the presence of the Lewis acid, undergoes reaction to produce the latter.

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