Elimination reactions Hoffmann product

Consider the elimination reaction below, which uses a strong, sterically hindered base (LDA). The product will be a double bond. This reaction will produce the Hoffmann product. Draw this product. 

So, if we look back at the reaction above, we find that the two possible products are monosubstituted and disubstituted double bonds. Whenever you have an elimination reaction where more them one possible double bond can be formed, we have names for the different products based on which one is more substituted and w hich one is less substituted. The more substituted product is called the Zaitsev product, and the less substituted product is called the Hoffmann product. Usually you get the Zaitsev product, but under special circumstances you can get the Hoffman product. If you use a strong, sterically hindered base, you can form the Hoffman product. 

Vinyl substitutions on alkenes not having their double bonds conjugated with carbonyl groups often proceed more rapidly and give better product yields when the reactions are conducted in the presence of an unhindered secondary amine. Conjugated and nonconjugated dienes are usually only minor products in these cases. The major products normally are allylic amines obtained by nucleophilic attack of the secondary amine upon the ir-allylpalladium intermediates. Since allylic amines may be quatemized and subjected to the Hoffmann elimination, this is a two-step alternative to the direct vinyl substitution reaction.90... 

As CO is highly toxic, and causes respiratory problems, its elimination is quite important Industrially, CO elimination is required for C02 laser application, and the production of pure hydrogen for fuel cells. Catalysis testing of the reaction has been performed, independently, with an IR gas-sensor by Hoffmann et al. and with a combustible CO gas sensor by Yamada et al. [25, 26]. In both groups, C02 produced by CO oxidation was quantified by an IR gas-sensor. 

Reaction with a-silyltertiary aliphatic amines leads to results of the same type, including silyl- and non-sily 1-products, proceeding either from a Stevens rearrangement or a Hoffmann elimination.364... 

Another example is the reaction of benzyne with 1-methyl- (and benzyl)-3, 3-dimethylbenzo[d]-l,3-azasiloline (see their preparation in Section IV.A.2.p). Stevens rearrangement product is obtained (48%) as a single compound. If a Me on nitrogen is replaced by an Et, then Hoffmann elimination occurs.251 It should be noted that an Y-alkyl MSMA is converted into an Y-aryl RSMA in the former case and into a Y-aryl MSMA in the latter case. 

Structure 4 is an intermediate for manufaeturing vitamin A (Scheme 2). The annual demand for vitamin A is about 3000 tons. Major producers are BASF, Hoffmann-La Roche and Rhone-Poulenc Animal Nutrition [55]. At an early stage in the synthesis BASF and Hoffmann-La Roche are using a hydroformylation step to synthesize 4 starting from l,2-diacetoxy-3-butene (5) and 1,4-di-aeetoxy-2-butene (6), respectively [56, 57]. The selectivity toward the branched product in the BASF process is achieved by using an unmodified rhodium carbonyl catalyst at a high reaction temperature. The symmetry of 6 in La Roche s process does not lead to regioselectivity problems. Elimination of acetic acid and isomerization of the exo double bond (La Roche) yields the final product 4 in both processes. 

Now let us go one step further and investigate the homologue mesylate which containes one methylene group more in the side chain. When the alcohol 21 ) was attempted to mesylate, the desired derivative could not be isolated. The formation of the internal quaternary derivative is so fast, that this is the only product isolated in 71 % yield. This compound was very sluggish to react with sodium cyanide. The reaction has been performed in ethylene glycol at 200 Now no attack at an a-carbon with respect to the charged nitrogene occured, only an epimer-pair i2 ) was isolated in 68 % combined yield. Presumably a Hoffmann-type elimination is... 

In two-phase systems, absorption of mierowave radiation by dieleetrie heating and ionic conduction enables individual phases to be heated at different rates, potentially affording sizable temperature differenees. Raner et al. (1995) performed a Hoffmann elimination using a two-phase water-chloroform system The reaction carried out in water at 105 °C led to polymerization of the final product. However, the reaction proceeds adequately under microwave irradiation in a two-phase water-chloroform system. The temperatures of the aqueous and oiganie phases were 110... 

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