Acetals, 2-halo rearrangements

Second, one should take into account the stability of nitroso acetals (343) associated with the possibility of their rearrangement to give oxazines (344). In addition, it should be taken into account that cyclic nitroso acetals (343) can be transformed into halo derivatives of dihydrooxazines (345). (These transformations of nitroso acetals (343) will be considered in more detail in Section 3.5.4.3.3.)... 

Aliphatic and aryl aliphatic amino ketones are made by the amination of the halogenated carbonyl compounds, - e.g., dimethylaminoacetone (74%), l-diethylamino-2-pentanone (79%), and a-methylaminopropio-phenone (57%). It is noteworthy that this system may undergo a rearrangement, viz., ArCOCH,Br+ (C,H,),NH— ArCHjCON(C,H5)a (45%). The reaction of a-halo ketones with arylamines is even more complex. Examples of the formation of a-aminoaldehydes by this method are few. However, the same results may be achieved by the amination of the halo acetals with subsequent hydrolysis. "... 

Tertiary a-halo ketimines 3 reacted with alcohols in the presence of nitrogen bases, e.g. triethylamine, 1,4-diazabicyclo[2.2.2]octane, l,5-diazabicyclo[4.3.0]non-5-ene or 1,8-diaza-bicyclo[5.4.0]undec-7-ene, to afford mainly l-alkoxy-2,2-dialkylcyclopropylamines 4, together with variable amounts of a-alkoxy ketimines 5 and rearranged a-amino acetals 6. The geminal functionalized cyclopropanes 4, obtained in up to 80% yield, and the a-alkoxy ketimines 5, were formed via intermediate 2-(alkylamino)allylcarbenium ions 7. 

Anhydrous hydrogen chloride, bromide, or iodide will add to alkenes by a carbocationic mechanism to give Markovnikov products. The products may have rearranged structures if the first intermediate carbocation can improve in stability by a 1,2-hydride or alkyl shift. Addition to a, -unsaturated carbonyl compounds affords the -halo compounds (Eq. 6.46) [74], which are prone to elimination and thus often isolated as the acetals. Aqueous... 

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