This journal is c The Royal Society of Chemistry 2013 Chem. Commun., 2013, 49, 2189--2191 2189 Cite this: Chem. Commun., 2013, 49, 2189 Fluorinated 5- and 7-membered carbacycle motifs by reaction of difluorocarbene with acetylene ethers† Poh Wai Chia,z Davide Bello,z Alexandra M. Z. Slawin and David O’Hagan* The reaction of acetylene ethers with difluorocarbene (CF 2 ), gen- erated from the Ruppert–Prakash reagent, unexpectedly gave rise to co-produced fluorinated bicyclic [2.1.1]-hex-2-ene and cyclo- hepta-1,4-diene ring products. The Ruppert–Prakash 1 reagent (TMSCF 3 ) has shown consider- able versatility both as a nucleophilic trifluoromethyl carbanion ( À CF 3 ) donor 1,2 and as a source of difluorocarbene (:CF 2 ). 3,4 Recently it was demonstrated that when olefins or acetylenes are treated with TMSCF 3 and sodium iodide as a catalyst, the corresponding difluorocyclopropanes 1 and difluorocyclo- propenes 2 are efficiently generated indicating products arising by direct addition of the unsaturated substrates with difluoro- carbene. 4 These reactions are summarised in Scheme 1. In each case the R substituent of 1 and 2 in that study was aryl or aliphatic, not heterocyclic. As part of an ongoing programme exploring the nature of chains and rings containing the CF 2 group 5 we began to investigate the reaction of the Ruppert–Prakash reagent with acetylenic ethers to explore whether difluoromethylenecyclo- propene ethers (R = ÀOR 0 2) could be prepared. The outcome was surprising. Treatment of acetylene ethyl ether 3a with TMSCF 3 under the published 4 sodium iodide catalysed conditions gave two major fluorinated products. Separation of the two products proved to be difficult due to their similarly low polarity. Nevertheless, the major product was isolated as a crystalline solid, and X-ray structure analysis revealed the seven membered cyclohepta-1,4-diene ring product 4a as shown in Fig. 1a. At this stage we were unable to confidently assign a structure to co-produced 5a based on NMR and mass spectro- metry data. This product was a liquid and not easily amenable to X-ray analysis for structure elucidation. In order to generate a crystalline analogue of product class 5 the reaction was carried out using pBr-phenylacetylene ether 3b. This gave rise to the analogous products 4b and 5b, both of which were crystalline solids. Product 4b was shown (Fig. 1c) by X-ray analysis to again contain the cyclohepta-1,4-diene ring system. Structure analysis Scheme 1 In 2011 Wang et al., reported that the Ruppert–Prakash reagent reacts with olefins and acetylenes to generate difluoro-cyclopropanes and cyclopropenes respectively by direct difluorocarbene addition. 4 Fig. 1 X-ray structures of (a) 4a, (b) 5b and (c) 4b allowed structure determination of these novel fluorinated ring systems. University of St Andrews, School of Chemistry and Centre for Biomolecular Sciences, North Haugh, St Andrews, Fife, KY16 9ST, UK E-mail: do1@st-andrews.ac.uk; Fax: +44 (0)1334 463800; Tel: +44 (0)1334 467171 † Electronic supplementary information (ESI) available. CCDC 916377–916379. For ESI and crystallographic data in CIF or other electronic format see 10.1039/ c3cc39066g ‡ These authors contributed equally to this work. Received 19th December 2012, Accepted 25th January 2013 DOI: 10.1039/c3cc39066g www.rsc.org/chemcomm ChemComm COMMUNICATION Downloaded on 26 February 2013 Published on 28 January 2013 on http://pubs.rsc.org | doi:10.1039/C3CC39066G View Article Online View Journal | View Issue