Hofmann rearrangement

Last updated
Hofmann rearrangement
Named after August Wilhelm von Hofmann
Reaction type Rearrangement reaction
Identifiers
RSC ontology ID RXNO:0000410

The Hofmann rearrangement (Hofmann degradation) is the organic reaction of a primary amide to a primary amine with one less carbon atom. [1] [2] [3] The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to give an isocyanate intermediate. The reaction can form a wide range of products, including alkyl and aryl amines.

Contents

The Hofmann rearrangement Hofmann Rearrangement Scheme.png
The Hofmann rearrangement

The reaction is named after its discoverer, August Wilhelm von Hofmann, and should not be confused with the Hofmann elimination, another name reaction for which he is eponymous.

Mechanism

The reaction of bromine with sodium hydroxide forms sodium hypobromite in situ , which transforms the primary amide into an intermediate isocyanate. The formation of an intermediate nitrene is not possible because it implies also the formation of a hydroxamic acid as a byproduct, which has never been observed. The intermediate isocyanate is hydrolyzed to a primary amine, giving off carbon dioxide. [2]

Hoffman rearrangement.png

  1. Base abstracts an acidic N-H proton, yielding an anion.
  2. The anion reacts with bromine in an α-substitution reaction to give an N-bromoamide.
  3. Base abstraction of the remaining amide proton gives a bromoamide anion.
  4. The bromoamide anion rearranges as the R group attached to the carbonyl carbon migrates to nitrogen at the same time the bromide ion leaves, giving an isocyanate.
  5. The isocyanate adds water in a nucleophilic addition step to yield a carbamic acid (aka urethane).
  6. The carbamic acid spontaneously loses CO2, yielding the amine product.

Variations

Several reagents can be substituted for bromine. Sodium hypochlorite, [4] lead tetraacetate, [5] N-bromosuccinimide, and (bis(trifluoroacetoxy)iodo)benzene [6] can effect a Hofmann rearrangement.

The intermediate isocyanate can be trapped with various nucleophiles to form stable carbamates or other products rather than undergoing decarboxylation. In the following example, the intermediate isocyanate is trapped by methanol. [7]

The Hofmann rearrangement using NBS. Hoffmann Rearrangement NBS.png
The Hofmann rearrangement using NBS.

In a similar fashion, the intermediate isocyanate can be trapped by tert-butyl alcohol, yielding the tert-butoxycarbonyl (Boc)-protected amine.

The Hofmann Rearrangement also can be used to yield carbamates from α,β-unsaturated or α-hydroxy amides [2] [8] or nitriles from α,β-acetylenic amides [2] [9] in good yields (≈70%).

Applications

See also

Related Research Articles

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is a functional group with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

<span class="mw-page-title-main">Imine</span> Organic compound or functional group containing a C=N bond

In organic chemistry, an imine is a functional group or organic compound containing a carbon–nitrogen double bond. The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions.

In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

<i>N</i>-Bromosuccinimide Molecule

N-Bromosuccinimide or NBS is a chemical reagent used in radical substitution, electrophilic addition, and electrophilic substitution reactions in organic chemistry. NBS can be a convenient source of Br, the bromine radical.

<span class="mw-page-title-main">Curtius rearrangement</span> Chemical reaction

The Curtius rearrangement, first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of nucleophiles such as water, alcohols and amines, to yield a primary amine, carbamate or urea derivative respectively. Several reviews have been published.

The Strecker amino acid synthesis, also known simply as the Strecker synthesis, is a method for the synthesis of amino acids by the reaction of an aldehyde with ammonia in the presence of potassium cyanide. The condensation reaction yields an α-aminonitrile, which is subsequently hydrolyzed to give the desired amino acid. The method is used commercially for the production of racemic methionine from methional.

<span class="mw-page-title-main">Favorskii rearrangement</span>

The Favorskii rearrangement is principally a rearrangement of cyclopropanones and α-halo ketones that leads to carboxylic acid derivatives. In the case of cyclic α-halo ketones, the Favorskii rearrangement constitutes a ring contraction. This rearrangement takes place in the presence of a base, sometimes hydroxide, to yield a carboxylic acid but most of the time either an alkoxide base or an amine to yield an ester or an amide, respectively. α,α'-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.

<span class="mw-page-title-main">(Bis(trifluoroacetoxy)iodo)benzene</span> Chemical compound

(Bis iodo)benzene, C
6
H
5
I(OCOCF
3
)
2
, is a hypervalent iodine compound used as a reagent in organic chemistry. It can be used to carry out the Hofmann rearrangement under acidic conditions.

<span class="mw-page-title-main">Alpha-Haloketone</span>

In organic chemistry, an α-haloketone is a functional group consisting of a ketone group or more generally a carbonyl group with an α-halogen substituent. α-haloketones are alkylating agents. Prominent α-haloketones include phenacyl bromide and chloroacetone.

Di-<i>tert</i>-butyl dicarbonate Chemical compound

Di-tert-butyl dicarbonate is a reagent widely used in organic synthesis. Since this compound can be regarded formally as the acid anhydride derived from a tert-butoxycarbonyl (Boc) group, it is commonly referred to as Boc anhydride. This pyrocarbonate reacts with amines to give N-tert-butoxycarbonyl or so-called Boc derivatives. These carbamate derivatives do not behave as amines, which allows certain subsequent transformations to occur that would be incompatible with the amine functional group. The Boc group can later be removed from the amine using moderately strong acids. Thus, Boc serves as a protective group, for instance in solid phase peptide synthesis. Boc-protected amines are unreactive to most bases and nucleophiles, allowing for the use of the fluorenylmethyloxycarbonyl group (Fmoc) as an orthogonal protecting group.

The Lossen rearrangement is the conversion of a hydroxamate ester to an isocyanate. Typically O-acyl, sulfonyl, or phosphoryl O-derivative are employed. The isocyanate can be used further to generate ureas in the presence of amines or generate amines in the presence of H2O.

<i>tert</i>-Butyloxycarbonyl protecting group Protecting group used in organic synthesis

The tert-butyloxycarbonyl protecting group or tert-butoxycarbonyl protecting group is a protecting group used in organic synthesis.

<span class="mw-page-title-main">Lead(IV) acetate</span> Organometallic compound (Pb(C2H3O2)4)

Lead(IV) acetate or lead tetraacetate is an organometallic compound with chemical formula Pb(C2H3O2)4. It is a colorless solid that is soluble in nonpolar, organic solvents, indicating that it is not a salt. It is degraded by moisture and is typically stored with additional acetic acid. The compound is used in organic synthesis.

Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula H2NCOOH. It can be obtained by the reaction of ammonia NH3 and carbon dioxide CO2 at very low temperatures, which also yields ammonium carbamate [NH4]+[NH2CO2]. The compound is stable only up to about 250 K (−23 °C); at higher temperatures it decomposes into those two gases. The solid apparently consists of dimers, with the two molecules connected by hydrogen bonds between the two carboxyl groups –COOH.

Weerman degradation, also named Weerman reaction, is a name reaction in organic chemistry. It is named after Rudolf Adrian Weerman, who discovered it in 1910. In general, it is an organic reaction in carbohydrate chemistry in which amides are degraded by sodium hypochlorite, forming an aldehyde with one less carbon. Some have regarded it as an extension of the Hofmann rearrangement.

<span class="mw-page-title-main">Oseltamivir total synthesis</span>

Oseltamivir total synthesis concerns the total synthesis of the antiinfluenza drug oseltamivir marketed by Hoffmann-La Roche under the trade name Tamiflu. Its commercial production starts from the biomolecule shikimic acid harvested from Chinese star anise and from recombinant E. coli. Control of stereochemistry is important: the molecule has three stereocenters and the sought-after isomer is only 1 of 8 stereoisomers.

<span class="mw-page-title-main">Schmidt reaction</span> Chemical reaction between an azide and a carbonyl derivative

In organic chemistry, the Schmidt reaction is an organic reaction in which an azide reacts with a carbonyl derivative, usually an aldehyde, ketone, or carboxylic acid, under acidic conditions to give an amine or amide, with expulsion of nitrogen. It is named after Karl Friedrich Schmidt (1887–1971), who first reported it in 1924 by successfully converting benzophenone and hydrazoic acid to benzanilide. The intramolecular reaction was not reported until 1991 but has become important in the synthesis of natural products. The reaction is effective with carboxylic acids to give amines (above), and with ketones to give amides (below).

<span class="mw-page-title-main">Acyl azide</span>

Acyl azides are carboxylic acid derivatives with the general formula RCON3. These compounds, which are a subclass of organic azides, are generally colorless.

<span class="mw-page-title-main">Imidoyl chloride</span>

Imidoyl chlorides are organic compounds that contain the functional group RC(NR')Cl. A double bond exist between the R'N and the carbon centre. These compounds are analogues of acyl chloride. Imidoyl chlorides tend to be highly reactive and are more commonly found as intermediates in a wide variety of synthetic procedures. Such procedures include Gattermann aldehyde synthesis, Houben-Hoesch ketone synthesis, and the Beckmann rearrangement. Their chemistry is related to that of enamines and their tautomers when the α hydrogen is next to the C=N bond. Many chlorinated N-heterocycles are formally imidoyl chlorides, e.g. 2-chloropyridine, 2, 4, and 6-chloropyrimidines.

<span class="mw-page-title-main">2-Bromopyridine</span> Chemical compound

2-Bromopyridine is an organic compound with the formula BrC5H4N. It is a colorless liquid that is used as an intermediate in organic synthesis. It can be prepared from 2-aminopyridine via diazotization followed by bromination.

References

  1. Hofmann, A. W. (1881). "Ueber die Einwirkung des Broms in alkalischer Lösung auf Amide" [On the action of bromine in alkaline solution on amides]. Berichte der Deutschen Chemischen Gesellschaft. 14 (2): 2725–2736. doi:10.1002/cber.188101402242.
  2. 1 2 3 4 Everett, Wallis; Lane, John (1946). The Hofmann Reaction. Organic Reactions. Vol. 3. pp. 267–306. doi:10.1002/0471264180.or003.07. ISBN   9780471005285.
  3. Shioiri, Takayuki (1991). "Degradation Reactions". Comprehensive Organic Synthesis. Vol. 6. pp. 795–828. doi:10.1016/B978-0-08-052349-1.00172-4. ISBN   9780080359298.
  4. Mohan, Ram S.; Monk, Keith A. (1999). "The Hofmann Rearrangement Using Household Bleach: Synthesis of 3-Nitroaniline". Journal of Chemical Education. 76 (12): 1717. Bibcode:1999JChEd..76.1717M. doi:10.1021/ed076p1717.
  5. Baumgarten, Henry; Smith, Howard; Staklis, Andris (1975). "Reactions of amines. XVIII. Oxidative rearrangement of amides with lead tetraacetate". The Journal of Organic Chemistry. 40 (24): 3554–3561. doi:10.1021/jo00912a019.
  6. Almond, Merrick R.; Stimmel, Julie B.; Thompson, Alan; Loudon, Marc (1988). "Hofmann Rearrangement under Mildly Acidic Conditions using [I,I-Bis(Trifluoroacetoxy)]iodobenzene: Cyclobutylamine Hydrochloride from Cyclobutanecarboxamide". Organic Syntheses. 66: 132. doi:10.15227/orgsyn.066.0132.
  7. Keillor, Jeffrey W.; Huang, Xicai (2002). "Methyl Carbamate Formation via Modified Hofmann Rearrangement Reactions: Methyl N-(p-Methoxyphenyl)carbamate". Organic Syntheses. 78: 234. doi:10.15227/orgsyn.078.0234.
  8. Weerman, R.A. (1913). "Einwirkung von Natriumhypochlorit auf Amide ungesättigter Säuren". Justus Liebigs Annalen der Chemie. 401 (1): 1–20. doi:10.1002/jlac.19134010102.
  9. Rinkes, I. J. (1920). "De l'action de l'Hypochlorite de Sodium sur les Amides D'Acides". Recueil des Travaux Chimiques des Pays-Bas. 39 (12): 704–710. doi:10.1002/recl.19200391204.
  10. Maki, Takao; Takeda, Kazuo (2000). "Benzoic Acid and Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a03_555. ISBN   3527306730..
  11. Allen, C. F. H.; Wolf, Calvin N. (1950). "3-Aminopyridine". Organic Syntheses . 30: 3. doi:10.15227/orgsyn.030.0003.; Collective Volume, vol. 4, p. 45
  12. US 20080103334,"Process For Synthesis Of Gabapentin"

Bibliography