A HemN-like radical S-adenosyl-L-methionine (SAM) enzyme adds a SAM-based methylene radical generated via a radical relay to an sp2 carbon of substrate to produce a SAM-substrate covalent adduct, which is converted to the cyclopropane ring by a methyltransferase in the biosynthesis of natural product CC-1065.
Future long-term space travel and cis-lunar research platforms such as the Deep Space Gateway require a reliable life support system and - similarly to our demands on Earth - a renewable energy source. The production of so-called ‘solar fuels’, i.e. fuels such as hydrogen or long-chain hydrocarbons generated only from sunlight, water and carbon dioxide is currently investigated for terrestrial applications. These solar fuels are promising candidates for meeting the global quest for alternative energy sources. Currently, the most efficient systems comprise the ones operating according to the natural photosynthetic process: semiconductors are employed as light absorbers which transfer electrons upon photoexcitation to integrated electrocatalysts, catalyzing the respective half-cell reaction of water-splitting (photoanode) or fuel production (photocathode). Although, these systems are interesting as well for space applications from the point of oxygen and fuel generation, solar fuel production in microgravity environment has not been realized and investigated yet.
Carbyne, the elusive sp-hybridized linear allotrope of carbon, is a controversial material (Fig. a). It has fascinated scientists for decades because it ought to exist but all claims of its synthesis and identification in meteorites have turned out to be dubious. Many attempts have been made to prepare structures consisting exclusively of sp-carbon, either in linear or cyclic form. However, their inherent instability in a pristine form seems to result in immediate decomposition under standard conditions. Linear polyynes with enormous end-capping protective groups are, so far, the best isolable model system for carbyne. Wesley Chalifoux and Rik Tykwinski managed to make the longest known linear polyyne with 44 sp carbon atoms (22 consecutive triple bonds, Nature Chem. 2010, 2, 967). The Fritsch-Buttenberg-Wiechell (FBW) rearrangement is a valuable synthetic tool in the synthesis of these long molecular wires. In this rearrangement the 1,1-dibromoolefin is transformed undergoing a 1,2-shift to an acetylene upon treatment with a strong reducing agent (Fig. b).