2.2.2-Propellane
Encyclopedia
[2.2.2]Propellane, formally tricyclo[2.2.2.01,4]octane is an organic compound
, a member of the propellane
family. It is a hydrocarbon
with formula C8H12, or C2(=C2H4)3. Its molecule has three rings with four carbon
atoms each, sharing one C-C bond.
This compound is unstable (although not as much as [1.1.1]propellane
). The bond angles on the shared carbons are considerably strained: three of them are close to 90 degrees, the other three to 120 degrees. The strain energy
is estimated to be 93 kcal/mol (390 kJ/mol).
in 1973 by the group of Philip Eaton
(who had earlier obtained cubane
), according to the following scheme:
The synthesis begins with photochemical [2+2]cycloaddition
of ethylene
on the cyclohexene
derivative 1 to produce the bicyclic compound
2, followed by elimination reaction
with potassium t-butoxide of acetic acid
to cyclobutene 3, followed by another cycloaddition with ethylene to 4. This compound is converted to the diazo
ketone 5 by deprotonation (using acetic acid
and sodium methoxide
) and reaction with tosyl azide
. The ketone then undergoes Wolff rearrangement
to ketene
6. Ozonolysis
forms the ketone
7, another diazotation yields the ketene 8, which undergoes Wolff rearrangement again to the ketene 9. Reaction with dimethylamine
affords the [2.2.2]propellane backbone with a dimethylamide substituent 10.
The final product 10 was found to spontaneously isomerize in solution to the monocyclic amide
11, with a half-life of 28 minutes at room temperature.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
, a member of the propellane
Propellane
In organic chemistry, propellane is any member of a class of polycyclic hydrocarbons, whose carbon skeleton consists of three rings of carbon atoms sharing a common carbon-carbon covalent bond...
family. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
with formula C8H12, or C2(=C2H4)3. Its molecule has three rings with four carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms each, sharing one C-C bond.
This compound is unstable (although not as much as [1.1.1]propellane
1.1.1-Propellane
[1.1.1]Propellane is an organic compound, the simplest member of the propellane family. It is a hydrocarbon with formula C5H6 or C23. The molecular structure consists of three rings of three carbon atoms each, sharing one C-C bond....
). The bond angles on the shared carbons are considerably strained: three of them are close to 90 degrees, the other three to 120 degrees. The strain energy
Strain energy
In a molecule, strain energy is released when the constituent atoms are allowed to rearrange themselves in a chemical reaction or a change of chemical conformation in a way that:* angle strain,* torsional strain,* ring strain and/or steric strain,...
is estimated to be 93 kcal/mol (390 kJ/mol).
Synthesis
[2.2.2]Propellane was first synthesizedOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
in 1973 by the group of Philip Eaton
Philip Eaton
Philip E. Eaton is a Professor Emeritus of Chemistry at the University of Chicago. He and his fellow researchers were the first to synthesize the "impossible" cubane molecule in 1964....
(who had earlier obtained cubane
Cubane
Cubane is a synthetic hydrocarbon molecule that consists of eight carbon atoms arranged at the corners of a cube, with one hydrogen atom attached to each carbon atom. A solid crystalline substance, cubane is one of the Platonic hydrocarbons. It was first synthesized in 1964 by Philip Eaton, a...
), according to the following scheme:
The synthesis begins with photochemical [2+2]cycloaddition
Cycloaddition
A cycloaddition is a pericyclic chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction.Cycloadditions are usually described by the...
of ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
on the cyclohexene
Cyclohexene
Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes...
derivative 1 to produce the bicyclic compound
Polycyclic compound
In organic chemistry, a polycyclic compound is a cyclic compound with more than one hydrocarbon loop or ring structures . In general, the term includes all polycyclic aromatic compounds, including the polycyclic aromatic hydrocarbons, the heterocyclic aromatic compounds containing sulfur,...
2, followed by elimination reaction
Elimination reaction
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism...
with potassium t-butoxide of acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
to cyclobutene 3, followed by another cycloaddition with ethylene to 4. This compound is converted to the diazo
Diazo
Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms as a terminal functional group. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane...
ketone 5 by deprotonation (using acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
and sodium methoxide
Sodium methoxide
Sodium methoxide is a chemical compound, with formula CH3ONa. This colourless solid, which is formed by the deprotonation of methanol, is a widely used reagent in industry and the laboratory...
) and reaction with tosyl azide
Tosyl azide
Tosyl azide is a reagent used in organic synthesis.-Uses:Tosyl azide is used for the introduction of azide and diazo functional groups. It is also used as a nitrene source and as a substrate for [3+2] cycloaddition reactions.-Preparation:...
. The ketone then undergoes Wolff rearrangement
Wolff rearrangement
The Wolff rearrangement is a rearrangement reaction converting a α-diazo-ketone into a ketene. This reaction was first reported by Ludwig Wolff in 1912....
to ketene
Ketene
A ketene is an organic compound of the form R'RC=C=O. The term is also used specifically to mean ethenone, the simplest ketene, where R' and R are hydrogen atoms.Ketenes were first studied as a class by Hermann Staudinger.-Formation:...
6. Ozonolysis
Ozonolysis
Ozonolysis is the cleavage of an alkene or alkyne with ozone to form organic compounds in which the multiple carbon–carbon bond has been replaced by a double bond to oxygen...
forms the ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
7, another diazotation yields the ketene 8, which undergoes Wolff rearrangement again to the ketene 9. Reaction with dimethylamine
Dimethylamine
Dimethylamine is an organic compound with the formula 2NH. This secondary amine is a colorless, flammable liquified gas with an ammonia-like odor. Dimethylamine is generally encountered as a solution in water at concentrations up to around 40%...
affords the [2.2.2]propellane backbone with a dimethylamide substituent 10.
The final product 10 was found to spontaneously isomerize in solution to the monocyclic amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
11, with a half-life of 28 minutes at room temperature.