Alkynes fluoro

The first example of a cyclization of fluorine-containing 5-hexenyl radicals was the study of the radical-iniOated cyclodimenzation reaction of 3,3,4,4-tetra-fluoro-4-iodo-1-butene. In this reaction, the intermediate free radical adds either to more of the butene or to an added unsaturated species [54, 55] (equation 56). Electron-deficient alkenes are not as effective trapping agents as electron-nch alkenes and alkynes [55]. 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

As a direct consequence of Bent s rule,56 carbon compounds with a significant amount of s-character in their bonds to an electronegative element, e.g., fluoro-alkynes, are unstable. Thus, reactions which involve change in hybridization at a carbon atom bearing such an acceptor can be promoted when the amount of s-character at the reactive atom decreases. The role of rehybridization in a variety of chemical and supramolecular processes has been extensively analyzed and reviewed recently.55,58... 

Fuchigami and co-workers utilized the regioselective anodic fluorination of aryl propargyl sulfides 301 for the preparation of fluorinated alkyne intermediates, which were subsequently isomerized by sodium ethoxide to furnish 1-fluoro-l-arylthioallenes 302 (Scheme 8.80) [166]. 

The alkyne (15 mmol) is added to TBA-H2F3 (9 g, 30 mmol) in Cl(CH2)2Cl (l ml) and the mixture is protected from atmospheric moisture and heated until the reaction is complete. H20 (5 ml) is added and the mixture is extracted with Et20 (3 x 10 ml). The extracts are washed with H,0 to pH 5, dried (Na2S04), and evaporated to yield the Z- and f-fluoro-alkenes [e.g. MeOCOCF=CHC02Me (60°C, 30 h), 80% PhCF=CHC02Me (120°C,... 

The nickel-catalyzed electrochemical carboxylation of l-(perfluoroalkyl) aUcenes proceeds regioselectively to afford 4-fluoro-4-perfluoroalkyl-3-alkenoic acids via a Ni(II)-allyl complex and a final F elimination (Fig. 19) [107]. Electrochemical carboxylation of alkynes in the presence of... 

Similarly, l-bromo-l,l-difluoro-2-alkynes, which were prepared by the reaction of lithium acetylides with CF2ClBr [284] or CF2Br2 [285], also reacted with carbonyl compounds in the presence of zinc to afford the corresponding a,a-difluoropropargyl alcohol [285]. This reaction has been utilized for the preparation of 3-fluoro-2,5-disubstituted furans [286] and other fluorinated biologically active compounds [285,287] (Scheme 99). 

The electrophilic anti addition of benzeneselenenyl fluoride to C = C bonds has been performed in a one-pot reaction with, /V-(phenylselanyl)phthalimide/triethylamine tris(hydrogen fluoride) using disubstituted alkynes to give a-fluoro-/T(phenylselanyl)alkenes 4.217... 

Me2 AsH and the perfluorocycloalkene by addition/elimination.133 Fluoroaliphatic diarsines may be obtained from the addition of tetramethyldiarsine to fluoro-alkenes or -alkynes (equations 38 and 39).134... 

The phenylthiofluorination of alkynes using A -(phenylsulfanyl)phthalimide and hydrogen fluo-ride/pyridinc yields the substituted l-fluoro-2-(phenylsulfanyl)aIkencs... 

Besides processes (1) and (2), the reader should be aware that nucleophilic attacks on alkynes are treated in other chapters of this book, dealing with rearrangements, cyclizations, polyacetylenes, cyclic acetylenes and perhaps others. A number of publications overlap with ours in different ways and at different levels -. They treat individual alkynes or families " , e.g. acetylene, diacetylenes , acetylene dicarboxylic esters haloacetylenes , alkynyl ethers and thioethers > ynamines , fluoro-alkynes ethynyl ketpnes , nitroalkynes , etc. synthetic targets, e.g. pyrazoles , if-l,2,3-triazoles , isothiazoles , indolizines S etc. reagents, e.g. nitrones , lithium aluminium hydride , heterocyclic A -oxides - , azomethine ylids - , tertiary phosphorus compounds , miscellaneous dipolar nucleophiles - , etc. The reader will appreciate that all of these constitute alternate entries into our subject. 

Uneyama and coworkers reported electrochemical generation of PhSeF for fluoro-selenation of alkenes and alkynes and recycling of the selenenylating reagent [52] ... 

Fluoro-l-iodo-l-alkenes. These compounds are prepared from 1 -alkynes by the... 

Addition reactions of the Si-Si bonds across carbon-carbon triple bonds have been most extensively studied since the 1970s by means of palladium catalysts. In the early reports, palladium complexes bearing tertiary phosphine ligands, mostly PPh3, were exclusively employed as effective catalysts, enabling the alkyne bis-silylation with activated disilanes, i.e., disilanes with electronegative elements on the silicon atoms such as hydro [36], fluoro [37], chloro [38], and alkoxy-disilanes [39,40] and those with cyclic structure (Scheme 4) [41-44]. The bis-silylation reactions could be successfully applied to terminal alkynes and acetylenedicarboxylates to give (Z)-l,2-bis(silyl)alkenes, which are otherwise difficult to synthesize. 

Other alkenyl complexes have been formed by displacement of fluoride or chloride ion from fluoro-olefins by metal carbonyl anions, by reactions of the perfluoroalkenylsilver derivative with metal halide compounds, and by insertion of an alkyne into a metal-X bond, and parameters are given with structures [168] to [187]. (8, 86-91) As... 

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