Amine Hofmann elimination

The Hofmann elimination route, of which many versions exist, can be carried out at much lower temperatures in conventional equipment. The PX is generated by a 1,6-Hofmaim elimination of amine from a quaternary ammonium hydroxide in the presence of a base. This route gives yields of 17—19%. Undesired polymeric products can be as high as 80% of the product. In the presence of a polymerization inhibitor, such as phenothiazine, DPXN yields can be increased to 50%. 

Chloroazetidine i, R2CCN ii, hydrolysis iii, Hofmann 81GEP3027169 degradation of amine iv, elimination... 

The reactions of (174) with various amines has been studied." " Hydrolysis of the hexamine salt of (174) gave not the symmetric diamine but (184) via a cyclic intermediate. The pyrolysis of 5-methyl-2-thenyltrimethyl ammonium hydroxide (185) is claimed to give (186) through a 1,6 Hofmann elimination reaction. The Bischler-Napieralski cyclization has been applied to acetyl derivatives of 2-(2-thienyl) ethylamine and 2-(3-thienyl) ethylamine for the preparation of sulfur analogs of isoquinoline. ... 

The preparation of an alkene 3 from an amine 1 by application of a /3-elimination reaction is an important method in organic chemistry. A common procedure is the Hofmann elimination where the amine is first converted into a quaternary ammonium salt by exhaustive methylation. Another route for the conversion of amines to alkenes is offered by the Cope elimination. 

The Hofmann elimination is a classic route to olefins via alkylammonium hydroxides from amines. In the present instance it is employed in the generation of />-xylylene, a... 

What product would you expect from Hofmann elimination of the following amine ... 

Many of the reactions of amines are familiar from past chapters. Thus, amines react with alkyl halides in S 2 reactions and with acid chlorides in nucleophilic acyl substitution reactions. Amines also undergo E2 elimination to yield alkenes if they are first qualernized by treatment with iodomethane and then heated with silver oxide, a process called the Hofmann elimination. 

Name the following amine, including R,S stereochemistry, and draw the product of its reaction with excess iodomethane followed by heating with Ag20 (Hofmann elimination). Is the stereochemistry of the alkene product Z or E Explain. 

Coniine, C H N. is the toxic principle of the poison hemlock drunk by Socrates. When subjected to Hofmann elimination, coniine yields 5-(iV,N-dimethylamino)-l-octene. If coniine is a secondary amine, what is its structure ... 

Hofmann elimination (Section 24.7) The elimination reaction of an amine to yield an alkene by reaction with iodomethane, followed by heating with Ag2Q. 

The Hofmann elimination is useful synthetically for preparing alkenes since it gives the least substituted alkene. The reaction involves thermal elimination of a tertiary amine from a quaternary ammonium hydroxide these are often formed by alkylation of a primary amine with methyl iodide followed by reaction with silver oxide. The mechanism of the elimination is shown in Scheme 1.13 in this synthesis of 1-methyl-1-... 

Hofmann elimination reactions from hi- and tri-cyclic systems can, however, be used to create internal unsaturation without loss of a trialkyl amine as shown in Scheme 1.14 for the synthesis of the hexahydrothieno [ZjJazecine. 

A method for the preparation of olefins from primary amines is shown in equation 120. Treatment of 2-(4-bromophenyl)ethylamine (358) with acetic acid, acetic anhydride and sodium nitrite generates the nitroso amide 359, which decomposes to 4-bromostyrene in the presence of rhodium(II) acetate. The procedure is thus a mild, non-basic alternative to the classical Hofmann elimination of amines396,397. 

The Hofmann elimination converts an amine into an alkene. The process begins by converting an amine to a quaternciry cimmonium salt (that is, it has a nitrogen atom with four bonds). The general mechanism for the elimination step is in Figure 13-40. Figure 13-41 illustrates a sample reaction scheme for the Hofmann elimination. 

Hofmann Elimination Converts an amine into an alkene. 

When enamines are employed as sulfene traps, thiete 1,1-dioxides (e.g. 142) can be prepared by subsequent Hofmann elimination of amine. An alternative route to thiete 1,1-dioxides involves trapping sulfenes with ynamines, as illustrated by preparation of (144) (73S534). Certain thietes such as (145) (80LA873, 78TL3617, 78TL4839) are available directly from thioketones by 2 + 2 photocycloaddition with alkynes. 

Sodium hypochlorite reacts with (1) to give the 1-chloro derivative, which gives rise to a variety of products, including the bicyclic amine, pyrrolizidine, when treated with silver salts (72CJCH67). Quaternary salts derived from (3) react with sodium methoxide to give mostly the acyclic Hofmann elimination product (83%) minor amounts of (3) (14%) are also formed, together with a trace (2%) of the product of 5N2 attack on the a-methylene carbon (80JOC3952). 

Problem 18.30 Deduce the structures of the following amines from the products obtained from exhaustive methylation and Hofmann elimination, (a) C,H jN (A) reacts with 1 mol of CH,I and eventually yields propene. (6) CjHjjN (B) reacts with 2 mol of CHjI and gives ethene and a 3° amine. The latter reacts with 1 mol of CH,I and eventually gives propene. 

Problem 18.58 An optically active amine is subjected to exhaustive methylation and Hofmann elimination. The alkene obtained is ozonized and hydrolyzed to give an equimolar mixture of formaldehyde and butanal. What is the amine ... 

Base-catalysed quaternary ammonium salts give alkenes and 3° amines. This reaction is known as Hofmann elimination or Hofmann degradation. Amines can readily be converted to quaternary ammonium salt by the treatment of excess primary alkyl halides, and then Ag20 and H2O. Quaternary ammonium salts undergo E2 elimination, when heated with NaOH to give alkenes and tertiary amines. Thermal decomposition of a quaternary ammonium salt by NaOH to an alkene is known as Hofmann elimination. 

A. C. Cope and E. R. Trumbull, Olefins from amines the Hofmann elimination reaction and amine... 

The preparation of conjugated dienes from pyridines is exemplified by the transformation of 2-picoline into the sex pheromone (669) of Lobesia botrana, a major pest of vineyards (Scheme 154) (80TL67). Thus, the lithio salt of 2-picoline was alkylated by 2-(5-chloropentyl-oxy)tetrahydropyran, the resulting pyridine (665) N-methylated, and the pyridinium salt reduced by sodium borohydride. Quaternization of the 1,2,3,6-tetrahydropyridine (666) and Hofmann elimination gave the (7 , 9Z)-undecadien-l-ol (667) as the sole isomer. Protection of the alcohol and treatment of the corresponding ammonium salt (668) of the amine with lithium dimethylcuprate gave pure (669) after hydrolysis, acetylation and HPLC purification. 

Here, we envisage building the benzimidazole scaffold directly onto the linker and, by analogy with a regular tertiary amine synthesis on the REM linker, we can quaternize the resin-bound benzimidazole compounds by reaction with reactive bromides. The quaternary salt can then be liberated by a Hofmann elimination reaction upon treatment with base. 

Step 2 Hofmann elimination/Michael addition equilibrations. Acrylic acid functions as an efficient and selective trap for dimethyl amine vs. tert-butylamine, allowing for facile control of the equilibrium between 1 and 2. 

In protic electrolytes the solvent serves as proton donor for the anion. In aprotic solvents the anion either abstracts a jS-hydrogen from the tetraalkyl-ammonium cation of the supporting electrolyte to form alkane, alkene and t-amine in a Hofmann elimination, or at low salt concentration the alkyl bromide is deprotonated in a elimination to yield a mixture of RH, and RH(-H2) 417 ... 

J. K. Crandall, M. Apparu, Base-Promoted Isomerizations of Epoxides, Org. React. 1983, 29, 345—443. A. C. Cope, E. R. Trumbull, Olefins from Amines The Hofmann Elimination Reaction and Amine Oxide Pyrolysis, Org. React. 1960, 11, 317-493. 

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