DABCO

DABCO, short for1,4-diazabicyclo[2.2.2]octane, is one of a handful of molecules better known by their acronyms than by their full names¹. It is also frequently referred to as triethylenediamine, or TEDA.

DABCO has been known for at least 100 years, originally under the name quinolidine. In 1943, Otto Hromatka* and Eva Engel at the University of Vienna synthesized it via the cyclization of the dihydrobromide salt of 1-(2-bromoethyl)piperazine² or the dihydrochloride salt of 1-(2-chloroethyl)piperazine³. It is commercially produced by the catalytic thermolysis of ethylenediamine or 2-hydroxyethylamine.

Because of its two unhindered tertiary amine groups, DABCO is a strong base (pK_a1 of its conjugate acid = 3.0) and nucleophile. It is used as an alkaline catalyst in the production of polyurethane foams. As a Lewis base, it forms crystalline adducts with hydrogen peroxide and sulfur dioxide.

This year, DABCO was featured as the catalyst in two new syntheses. In April, Silong Xu and co-workers at Xi’an Jiaotong University (China) showed that it catalyzes [4 + 2] annulation reactions between 5-methylenehex-2-ynedioates and electron-deficient olefins such as 2-benzylidene-1H-indene-1,3-(2H)-dione to form spirocyclohexadiene adducts in yields up to 90% under mild conditions. Alternative catalysts gave poor yields or no reaction.

In July, Cunde Wang and colleagues at Yangzhou University (China) reported the use of DABCO to promote another set of cyclization reactions. In their process, substituted 2-amino-4H-chromen-4-ones and substituted 2,6-dibenzylidenecyclohexan-1-ones react to form 7,8,9,10-tetrahydro-12H-chromeno[2,3-b]quinolin-12-ones, also under mild conditions and in optimized yields of >80%. As with the Xu process, other basic catalysts gave significantly poorer yields.

1. Another is TEMPO, which will appear as a Molecule of the Week later this year.
2. CAS Reg. No. 89727-93-5.
3. CAS Reg. No. 34782-06-4.