It is soluble in many solvents, such as alcohols, ethers, haloalkanes, esters, and also is miscible with polar aprotic solvents. Cyclohexenone reacts both ketones and alkenes. It has an electron-poor carbon-carbon double bond as a typical representative of the α, β-unsaturated carbonyl compounds. With strong bases, the positions 4 and 6 are deprotonated.
Synthesis
There are several different synthetic routes for the production of cyclohexenone. The reduction following acid hydrolysis of 3-ethoxy-2-cyclohexen-1-one is available for the laboratory scale. The precursor is accessible from resorcinol through 1,3-cyclohexanedione. Anisole is also available. Cyclohexanone is obtained by Birch reduction followed by acid hydrolysis. It can be obtained from cyclohexanone by α-bromination and elimination, or from 3-chloro cyclohexene by means of hydrolysis and oxidation. Technically is 2-cyclohexen-1-one produced by catalytic oxidation of cyclohexene, for example with hydrogen peroxide and vanadium catalysts. There are several patented process variants with different oxidizing agents or catalysts.
Reagent
Cyclohexenone is a widely used building block in organic synthesis chemistry, as it offers many different ways to extend molecular frameworks. Cyclohexenone is easily adapted to Michael addition with nucleophiles or, it could be employed by a Diels-Alder reaction with electron-rich dienes. Furthermore, this compound reacts with organocopper compounds from 1,4-addition, or with Grignard reagents 1,2-addition, i.e., with attack of the nucleophile at the carbonyl carbon atom. Cyclohexenone is also used in multi-step synthesis in the construction of polycyclic natural products. Cyclohexenone was accidentally found to be an in-vitro catalyst for a relatively mild decarboxylation of alpha amino acids in 1986. Researchers in Japan were attempting to use t-butyl peroxide as a catalyst for decarboxylation using a solvent choice of cyclohexanol. Curiously they found that when they used lower-purity cyclohexanol, the reaction proceeded as much as 4 times faster compared to when they used relatively pure cyclohexanol. They found that cyclohexanol contained cyclohexenone as a natural impurity, which was three times more abundant in the technical grade cyclohexenone compared to the more purified cyclohexanol. Further research showed that 1% cyclohexenone in cyclohexanol will decarboxylate most alpha-amino acids, including non-standard ones, with a yield of 80-95% in a matter of several hours. The exceptions are certain amino acids like histidine, which was reported to take over 26 hours, and poly-amino acids, which fail to decarboxylate using 2-cyclohexenone and another route must be found instead.
