Isatin, also known as tribulin, is an
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
derived from
indole
Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...
with formula C
8H
5NO
2. The compound was first obtained by Otto Linné Erdman and Auguste Laurent in 1840 as a product from the oxidation of
indigo dye
Indigo dye is an organic compound with a distinctive indigo, blue color. Indigo is a natural dye obtained from the leaves of some plants of the Indigofera#Uses, ''Indigofera'' genus, in particular ''Indigofera tinctoria''. Dye-bearing ''Indigofer ...
by
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
and
chromic acids.
Isatin is a well-known natural product which can be found in plants of the genus ''
Isatis'', in ''
Couroupita guianensis
''Couroupita guianensis'', known by a variety of common names including cannonball tree, is a deciduous tree in the flowering plant family Lecythidaceae. It is native to lowland tropical rainforests of Central and South America, from Costa Rica, ...
'', and also in humans, as a metabolic derivative of
adrenaline
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...
.
It looks like a red-orange powder, and it is usually employed as building block for the synthesis of a wide variety of
biologically active compounds including
antitumorals,
antivirals
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Antiviral drugs are a class of antimicrobials ...
, anti-HIVs, and
antituberculars.
The isatin core is also responsible for the color of “
Maya blue
Maya blue () is a unique bright turquoise or azure blue pigment manufactured by cultures of pre-Columbian Mesoamerica, such as the Mayas and Aztecs, during a period extending from approximately the 8th century to around 1860 CE. It is found in ...
” and “Maya yellow” dyes.
It is rumored that isatin is a MAOI with dopaminergic properties.
Synthesis
Sandmeyer methodology
The Sandmeyer methodology is the oldest and straightforward way for the synthesis of isatin. The method involves the condensation between
chloral hydrate
Chloral hydrate is a geminal diol with the formula . It was first used as a sedative and hypnotic in Germany in the 1870s. Over time it was replaced by safer and more effective alternatives but it remained in use in the United States until at ...
and a primary arylamine (e.g.
aniline
Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...
), in the presence of
hydroxylamine hydrochloride
Hydroxylammonium chloride is a chemical compound with the formula . It is the hydrochloric acid salt of hydroxylamine (). Hydroxylamine is a biological intermediate in nitrification (biological oxidation of ammonia with oxygen into nitrite) and ...
, in aqueous
sodium sulfate
Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 mill ...
to form an α‐isonitrosoacetanilide. Isolation of this intermediate and subsequent
electrophilic cyclization promoted by strong acids (e.g.
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
) furnishes isatin in >75% yield.
Stolle methodology
The Stolle procedure is considered the best alternative to Sandmeyer methodology for the synthesis of both substituted and unsubstituted isatins. In this case primary or secondary arylamines are condensed with
oxalyl chloride
Oxalyl chloride is an organic chemical compound with the formula . This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.
Preparation
Oxalyl chloride was first prepared in 1892 by the ...
to form a chlorooxalylanilide intermediate which can then cyclize in the presence of a
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...
(e.g.
aluminium trichloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms a hexahydrate with the formula , containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are col ...
,
titanium tetrachloride
Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds o ...
,
boron trifluoride
Boron trifluoride is the inorganic compound with the formula . This pungent, colourless, and toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.
Structure and bonding
The g ...
, ''etc''.).
Other procedures
More recent approaches to the synthesis of N-substituted isatins involves the direct
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
of commercially available, substituted indoles or oxindoles with different
oxidizing agents
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
such as
TBHP,
IBX-SO3K,
tBuONO ''etc''.
Reactivity
The presence of an
aromatic ring
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The e ...
, a
ketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
and a
γ-lactam moiety, gives to isatin the rare potential to be used as both an
electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an ...
and a
nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
: indeed, it undergoes an enormous number of reactions, such as N-substitutions,
electrophilic aromatic substitution
Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitut ...
at positions C-5 and C-7 of the phenyl ring,
nucleophilic additions onto the C-3
carbonyl group
In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes ...
,
chemoselective reductions,
oxidations,
ring-expansions and
spiro-annulations. Because of this unique reactivity, isatin is considered one of the most valuable
building blocks in
organic synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...
.
''N''-Substitution
The ''N''-functionalization of the isatin core can be readily obtained by the
deprotonation
Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...
of the amino moiety, forming the corresponding
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
or
potassium salt
In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). T ...
, and subsequent addition of an
electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an ...
(e.g. alkyl or acyl
halides
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluo ...
).
On the other hand, ''N''-arylation is usually achieved by
cross-coupling reactions with
aryl halides using
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
or
palladium catalysts.
Ring expansion
In the field of
organic synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...
,
ring expansions are considered valuable reactions since they allow the obtainment medium-size ring (7-9 atoms) which are difficult to synthesize through "classical" methods.
To date, only few articles concerning the ring expansion of isatin derivatives has been reported.
The first one is an acid-catalyzed one-pot
multicomponent reaction involving isatins, aminouracils, and isooxazolones to form isoxazoquinolines, important
scaffolds in
medicinal chemistry
Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacy involved with drug design, designing and developing pharmaceutical medication, drugs. Medicinal chemistry involves the identification, ...
.

In another one-pot
multicomponent reaction, a unique two-carbon expansion has been achieved by reacting isatin with indene-1,3-dione and N-substituted
pyridinium bromide to form dibenzo
,dzepin-6-ones.
''C-2''/''C-3'' nucleophilic addition
Isatin suffers
nucleophilic addition
In organic chemistry, a nucleophilic addition (AN) reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic addit ...
on
carbonyls at ''C-2'' and ''C-3'' positions. The
regioselectivity
In organic chemistry, regioselectivity is the preference of chemical bonding or breaking in one direction over all other possible directions. It can often apply to which of many possible positions a reagent will affect, such as which proton a str ...
of the process strongly depends both on the
substrate
Substrate may refer to:
Physical layers
*Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached
** Substrate (aquatic environment), the earthy material that exi ...
(properties of the
substituents
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety (chemistry), moiety in the resultant (new) molecule.
The suffix ''-yl'' is used when naming organic compounds that conta ...
on the isatin core, especially those bonded to the nitrogen atom) and the reaction conditions (
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
, temperature etc.). In some cases the
nucleophilic addition
In organic chemistry, a nucleophilic addition (AN) reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic addit ...
could be followed by secondary reactions (''e.g.''
cyclization
A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...
,
ring expansion,
ring opening ''etc.'')
Oxidation
The oxidation of isatin using
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
(
Baeyer–Villiger oxidation
The Baeyer–Villiger oxidation is an organic reaction that forms an ester from a ketone or a lactone from a cyclic ketone, using peroxyacids or peroxides as the oxidant. The reaction is named after Adolf von Baeyer and Victor Villiger who first ...
) or
chromic anhydride yields
isatoic anhydride,
a compound widely used either in
herbicide
Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
products and in
medicinal chemistry
Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacy involved with drug design, designing and developing pharmaceutical medication, drugs. Medicinal chemistry involves the identification, ...
. The use of
peroxydisulfuric acid
Peroxydisulfuric acid is an inorganic compound with a chemical formula . It is also called Marshall's acid after Professor Hugh Marshall, who discovered it in 1891.
Structure and bonding
This oxoacid features sulfur in its +6 oxidation state a ...
gives rise to
1,4‑benzoxazine compounds.
Dimerization
Dimerization of isatin with
KBH4 in methanol yields
Indirubin
Indirubin is a chemical compound most often produced as a byproduct of bacterial metabolism. For instance, it is one of the compounds responsible for the generally benign condition purple urine bag syndrome, resulting from bacteria metabolizing in ...
.
This represents the
indigo pigment's red component and a highly effective
cytotoxic
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are toxic metals, toxic chemicals, microbe neurotoxins, radiation particles and even specific neurotransmitters when the system is out of balance. Also some types of dr ...
compound.
Reduction
Reduction of the non-amide carbonyl group obviously occurs to give
oxindole
Oxindole (2-indolone) is an aromatic heterocyclic organic compound with the formula . It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing ring. Oxindole is a modified indoline with a ...
, respectively.
See also
*
Pfitzinger reaction
References
Reviews
*
*
*
*
External links
*{{cite EB1911 , wstitle=Isatin , volume=14 , pages=865–866 , short=1
Lactams
Oxindoles