A triply twisted Möbius annulene

26 June 2014 - Compound of Interest

mobius2.PNGThere is Möbius aromaticity news. A new compound having such aromaticity has been reported as synthesised by Schaller et al. in Nature Chemistry (DOI). The challenge: the creation of a large pi-ring (as in a regular aromatic compound) but then with one or more twists in it. As in a Möbius ring. The gain in aromaticity should offset the gain in strain. That is the theory but the authors confess that initially the project looked "fairly hopeless". They then found inspiration from a simple observation that telephone cords tend to wind around themselves in order to release strain, something called projection of twist into writhe. DNA supercoiling has something to do with it as well. The solution would then be to synthesise a compound that has writhes built in that then would convert back to twists. Schaller et al. ultimately came up with a compound that can be viewed as a cyclotrimer of three helicene units fitted with diacetylenic arms. This unusual compound called for unusual reaction conditions and the final ring-closing reaction (an Eglington coupling of two terminal alkynes) took three weeks for a 10% yield.