Acetylene, HC≡CH, is one of the primary building blocks in synthetic organic and industrial chemistry. Several highly valuable processes have been developed based on this simplest alkyne and the development of acetylene chemistry has had a paramount impact on chemical science over the last few decades. However, in spite of numerous useful possible reactions, the application of gaseous acetylene in everyday research practice is rather limited. Moreover, the practical implementation of high-pressure acetylene chemistry can be very challenging, owing to the risk of explosion and the requirement for complex equipment; special safety precautions need to be taken to store and handle acetylene under high pressure, which limit its routine use in a standard laboratory setup. Amazingly, recent studies have revealed that calcium carbide, CaC2 , can be used as an easy-to-handle and efficient source of acetylene for in situ chemical transformations. Thus, calcium carbide is a stable and inexpensive acetylene precursor that is available on the ton scale and it can be handled with standard laboratory equipment. The application of calcium carbide in organic synthesis will bring a new dimension to the powerful acetylene chemistry.

Attempts originally directed towards the generation of ferrocyne (1,2-dehydroferrocene, 4) and ferrocenediyne (1,2,1',2'-tetradehydroferrocene, 5) by triflate elimination from the respective ferrocenyl triflates led to the discovery of the first anionic thia-Fries rearrangements at a five-membered ring. These reactions take place with remarkable efficiency under very mild reaction conditions and yield the respective trifluoromethylsulfonyl-substituted ferrocenols. Most remarkably, the reaction starting from 1,1'-ferrocenediyl ditriflate (9) adopts an extremely high interannular stereoinduction in that exclusively the meso rearrangement product, meso-2,2'-bis(trifluoromethylsulfonyl)-1,1'-ferrocenediol (16), is formed, the corresponding racemic product 17 is not observed. It is shown that the second anionic thiaFries rearrangement proceeds at a much larger rate than the first one. The stereochemistry and the high rate of this reaction are explained on the basis of electronic as well as steric considerations. The redox behavior of some of the unprecedented ferrocene derivatives has been characterized by cyclovoltammetry.

Upon ortho lithiation ferrocenyl triflate and 1,1′-ferrocenediyl ditriflate undergo anionic thia-Fries rearrangements instead of triflate elimination. To differentiate between an ortho metalation and an ortho deprotonation, 2-(trimethylsilyl)ferrocenyl triflate was shown to undergo an anionic thia-Fries rearrangement to 2-((trifluoromethyl)sulfonyl)ferrocenol (5) in 84% yield upon treatment with tetrabutylammonium fluoride. Metalation of the respective tributylstannyl derivative with butyllithium also led to 5 in 99% yield as the result of the anionic thia-Fries rearrangement. 2-Methoxyferrocenyl triflate also underwent the rearrangement upon ortho deprotonation with lithium diisopropylamide in practically quantitative yield at low temperature. The electron-rich 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenolate was generated from 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenyl acetate. However, ortho deprotonation again afforded the anionic thia-Fries rearrangement product. These results clearly show that even very electron rich ferrocene derivatives undergo an anionic thia-Fries rearrangement instead of a triflate elimination. In an attempt to induce an elimination supported by steric crowding, 2,3,4-trimethylferrocenyl triflate was deprotonated, giving 3,4,5-trimethyl-2-((trifluoromethyl)sulfonyl)ferrocenol in quantitative yield as the result of an anionic thia-Fries rearrangement. As an alternative to the triflates ferrocenyl imidazolylsulfonate was tested as the starting material. While this compound could not be deprotonated, the corresponding 2-trimethylsilyl derivative reacted with tetrabutylammonium fluoride in a very unusual reaction to give diferrocenyl sulfate in almost quantitative yield.

The direct vinylation of an OH group in alcohols and phenols was carried out utilizing a novel CaC 2 /KF solid acetylene reagent in a simple K 2 CO 3 /KOH/DMSO system. The functionalization of a series of hydroxyl-group-containing substrates and the post-modification of biologically active molecules were successfully performed using standard laboratory equipment, providing straightforward access to the corresponding vinyl ethers. The overall process developed involves an atom-economical addition reaction employing only inorganic reagents, which significantly simplifies the reaction set-up and the isolation of products. A mechanistic study revealed a dual role of the F − additive, which both mediates the surface etching/renewal of the calcium carbide particles and activates the CuC bond towards the addition reaction. The development of the fluoride-mediated nucleophilic addition of alcohols eliminates the need for strong bases and may substantially extend the areas of application of this attractive synthetic methodology due to increasing functional group tolerance. As a replacement for dangerous and difficult to handle high-pressure acetylene, we propose the solid reagent CaC 2 /KF, which is easy to handle, does not require dedicated laboratory equipment and demonstrates enhanced reactivity of the acetylenic triple bond.Theoretical calculations have shown that fluoride-mediated activation of the hydroxyl group towards nucleophilic addition significantly reduces the activation barrier and facilitates the reaction. † Electronic supplementary information (ESI) available. CCDC 1444527 and 1444530. For ESI and crystallographic data in CIF or other electronic format see

The generation of (η6‐aryne)chromium complexes as reactive intermediates was investigated in two ways. Although earlier attempts directed towards triflate eliminations from a variety of tricarbonyl(phenyl triflate)chromium complexes had failed, more electron‐rich phenyl triflate complexes were considered. This was accomplished either by substitution with two methoxy groups in the arene ligand or by replacement of one of the three carbonyl ligands of the tricarbonylchromium complex with triphenylphosphane. However, the attempted elimination still did not take place; in spite of the increased electron densities in the aromatic ligands, anionic thia‐Fries rearrangements were observed in high yields at –78 °C. As an alternative, elimination of lithium fluoride was tested. Tricarbonyl(2‐lithiofluorobenzene)chromium(0) was generated by tin/lithium exchange. After hydrolytic workup, tricarbonyl(fluorobenzene)chromium was obtained as the main product, indicating that the lithiation step had been successful. A dimeric side product provided evidence for the intermediacy of (benzyne)tricarbonylchromium.