Swiss chemists have carried out a complete enantioselective synthesis of one of the isomers of tetramantane, built from four articulated adamantane fragments. To do this, they used a catalytic reaction of carbene insertion into a carbon-hydrogen bond. Previously, chemists had failed to obtain such compounds, and they were extracted from fossil fuels, write the authors of a preprint posted on the Chemrxiv.org portal.
The adamantane molecule is a tricyclic carbon framework that can be thought of as a small three-dimensional unit of the diamond crystal structure. Because of this, adamantane itself and compounds in which adamantane molecules are fused together are called diamondoids. They are difficult to obtain in the laboratory because they do not contain any functional groups and often exist as several isomers that are similar to each other.
But recently, Xiao-Yu Li and Christoph Sparr of the University of Basel have made progress in this direction. They have synthesized one of the spatial isomers of tetramantane, skewed tetramantane, in optically pure form. The scientists began by taking 2-bromotriamantane and introducing it into a photochemical reaction with a derivative of benzyl acrylate, as a result of which a chain of three carbon atoms was attached to the triamantane skeleton. The scientists then modified this chain so that at its end there was a group of two nitrogen atoms, which was needed to generate the carbene particle.
The next stage of the synthesis was key to building the tetramantane skeleton. The idea was to mix the resulting diazo compound with a rhodium catalyst. This, they assumed, would produce a rhodium carbenoid capable of inserting into carbon-hydrogen bonds. The problem was that there were many carbon-hydrogen bonds next to the carbenoid, and the reaction could result in eight different products. So the chemists had to test many different catalysts and reaction conditions, but in the end they obtained the only isomer they needed in optically pure form with a yield of 97 percent.
The chemists then completed the tetramantane skeleton using ring expansion and other manipulations of functional groups. In the final step, they mixed bromotetramantane with an iridium catalyst, tris(trimethylsilyl)silane, and irradiated the reaction mixture with blue light, which caused the bromine atom to detach, leaving pure, skewed tetramantane.
The complete enantioselective synthesis of tetramantane took 17 preparative stages, and the scientists confirmed its structure by comparing the obtained NMR spectra with previously published spectra of natural tetramantane. As the chemists note, this is the first targeted synthesis of a diamondoid with four articulated adamantane fragments.
Earlier we talked about how chemists carried out a complete synthesis of the fugu fish poison - tetrodotoxin.
