Methodologies, tools for synthesis - Reactive small species

For several decades, we have investigated the synthesis of unstabilized compounds. Recently, we synthesized cycloalkylimines by dehydrocyanation of the corresponding α-aminonitriles. Thus, the imines with a four to eight membered ring were synthesized for the first time. The largest ones are stable enough to undergo tautomerism by deuteration of the 4 hydrogen atoms on the carbon in α-position of the imino group.

We have also extensively studied the compounds detected in the interstellar medium (ISM) in the aim to identify new target compounds which could be present in this medium. About 200 molecules have been detected in the ISM since the first one in 1937. Many of them are organics. Thus, the millimeter spectra of many compounds including cyanates, nitriles, hemiacetal and several unstabilized imines have been synthesized. Their millimeter wave spectra were recorded in collaborations with spectroscopists in France or Europa before sending them to astrophysicists in Europa or in the USA. Methoxymethanol (CH3OCH2OH) has thus been observed in the ISM and the detection of hydroxyacetonitrile (CH3OCN) by an italian team shortly followed our publication of the spectrum. We also participated to various studies on methylisocyanate which was detected in Orion.

Cyanopolyynes, the formula of which is H-(C☰C)_n-CN, are probably the most interesting organic compounds detected so far in the interstellar medium. However, their synthesis in the laboratory is very challenging because of their instability. Even though the first member of the family, the cyanoacetylene (n=1), was synthesized in 1910, our group was the first to synthesize the next member of the family, the cyanobutadiyne (n = 2). Its reactivity has thus been investigated, as well as some mechanisms that could lead to this compound in the interstellar medium or the atmosphere of Titan. The methylated counterpart H3C-(C☰C)₂-CN has also been investigated in the context of space science.

In order to synthesize the following members of this family, we synthesized the bromocyanobutadiyne (Br-C☰C-C☰C-CN) and reacted it with terminal acetylenes. Contrary to what was anticipated, the corresponding cyanopolyynes were not obtained but other complex molecules were isolated, following an unprecedented mechanism.

We recently studied the sequence of [2+2]cycloaddition-retroelectrocyclization between ynamides and tetracyanoethylene. Actually, we carried out a methodology showing that it was possible to obtain 1,1,4,4-tetracyanobutadienes from several ynamides and tetracyanoethylene by simply mixing them together in dichloromethane at room temperature. This reaction is very tolerant to numerous substituents. We are currently investigating the possibility to extend this methodology to more complex systems and to study their optical properties.

For more information : Jean-Claude Guillemin, Yann Trolez