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The coupling reaction of terminal alkynes with organic halides, Sonogashira-(Hagihara) coupling, takes place with only 2 equivalents of dilute aqueous ammonia as an additive. The reaction of phenylacetylene and 4-iodoanisole in the presence of 1 mol% of PdCl2(PPh3)2, 2 mol% of CuI, and 2 equiv of aqueous ammonia in THF proceeds at room temperature for 6 h to afford the coupling product in a quantitative yield.

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Iridium-catalyzed CÀC bond-forming reactions have recently attracted much attention. [1] However, the reaction with main group organometallic reagents containing elements such as boron, tin, and silicon has not been demonstrated so far. Although carbon±carbon bond formation with such main group reagents with an a,b-unsaturated carbonyl compound has been reported recently to undergo a Mizoroki±Heck-type or conjugate addition reaction with palladium, [2] rhodium, [3] and ruthenium [4] catalysts, the specific nature of the metal catalysts largely influences the reaction mechanism as well as the reaction course. Herein, we report that an iridium catalyst effects the Mizoroki±Heck-type addition/elimination reaction of a,b-unsaturated carbonyl compounds with several organosilicon reagents, and constitutes the first C À C bond formation with a main group reagent. [5] The reaction of PhSi(OMe) 3 (1) with butyl acrylate (2 a) in the presence of 5 mol % of [{IrCl(cod)} 2 ] (cod ¼ 1,5-cyclooctadiene) and tetrabutylammonium fluoride (TBAF) in toluene/H 2 O (6/1) at 120 8C for 24 h afforded the addition/ elimination product 3 a in 71 % yield while the conjugate addition product 4 a was not obtained at all. This result sharply contrasts that of the related reaction with the rhodium catalyst [{RhCl(cod)} 2 ] at 608C in THF/H 2 O (6/1), which affords the conjugate adduct 4 a as the major product with high selectivity, 3 a/4 a ¼ 3/97 (Scheme 1). [6] In contrast to the combination of silicon reagent 1 and TBAF under anhydrous conditions, which is highly effective for the palladiumcatalyzed cross-coupling reaction with organic halides, [7] the rhodium-or iridium-catalyzed reaction of this combination with 2 a proceeded only very slightly without the addition of water. Table 1 summarizes the iridium-catalyzed Mizoroki± Heck-type addition/elimination reactions of several organosilicon reagents with a,b-unsaturated carbonyl compounds. Both iridium chloride and methoxide exhibited similar reactivities in the reactions with TBAF. The reaction also proceeded in THF/H 2 O at lower temperature (70 8C), although a small amount of conjugate addition product was formed (70/5). Several aryl silanes bearing a substituent on the aromatic ring also effected the reaction. Although the reaction of an ortho-substituted aryl silane was found to be slightly slower, the Mizoroki±Heck-type product was selectively obtained over the 1,4-addition product. Alkenylsilanes, which were prepared by hydrosilylation of alkynes, could also effect the reaction to afford a diene in 67 % yield.Aryl silanediols (7±9) were also found to participate in the addition/elimination reaction. By contrast to alkoxysilanes, silanediols effected the reactions without addition of TBAF and water. However, no reaction occurred when [{IrCl(cod)} 2 ] was used as the catalyst. Only [{Ir(OMe)(cod)} 2 ] was found to be an effective catalyst. Worthy of note is that the reaction with silanediols can be a halogen-free process, which is in contrast to the palladium-catalyzed Mizoroki±Heck ...

Arylation and alkenylation of aromatic aldehydes with silanediols is shown to proceed by use of a catalytic amount of rhodium complex. Treatment of ethyl(4-methoxyphenyl)silanediol with benzaldehyde in the presence of 3 mol% of [Rh(OH)(cod)] 2 affords 4-methoxyphenyl(phenyl)methanol in 59% yield after stirring at 70°C for 24 hours. On the other hand, diarylketone was also obtained at elevated temperature via b-hydride elimination from intermediary rhodium alkoxide.Nucleophilic addition of aryl-and alkenyl-metal reagents to carbonyl compounds has been a fundamental reaction in organic synthesis. By contrast to the highly reactive organometallic nucleophilic reagents such as lithium or magnesium, use of an organosilicon reagent has rarely been studied so far. 1-3 We have recently been studying the synthetic application of silanols, a new class of organosilicon reagent bearing hydroxy groups on the silicon atom, and revealed that the carbon-silicon bond of silanols successfully affect several carbon-carbon bond-forming reactions by the catalysis of a transition metal complexes. 4 Indeed, we reported that organosilicon reagents bearing hydroxy groups on the silicon atom affect Mizoroki-Heck (MH) type reaction and conjugate addition to a,b-unsaturated carbonyl compounds in the presence of a catalytic amount of a rhodium complex. 5 Hence, we envisaged the addition of such aryl-and alkenylsilanediols to aldehydes with the rhodium catalyst.The reaction of ethyl(4-methoxyphenyl)silanediol (1) with benzaldehyde (2a) was carried out in the presence of 3 mol% of [Rh(OH)(cod)] 2 in THF at 70 °C, which conditions were similar to those for the MH-type reaction of a,b-unsaturated carbonyl compounds. 5 The corresponding secondary alcohol was obtained in 59% yield after stirring for 24 hours as shown in the Equation.The table summarizes the results on the rhodium-catalyzed reactions of several aldehydes and silanediols. The reaction with twice molar amounts of silanediol to aldehyde was found to be optimum. A cationic rhodium complex, [Rh(cod)(CH 3 CN) 2 ]BF 4 similarly catalyzed the addition reaction. However, addition of several phosphines as a ligand of the rhodium complex inhibited the reaction. A polar and non-aqueous solvent such as THF, DME, or 1,4-dioxane was found to be excellent, while use of water as co-solvent resulted in no reaction by contrast to the related reaction with boronic acid. 3a-c A protic solvent, MeOH was also found to be uneffective. Aromatic aldehydes bearing an electron-donating or -withdrawing group 2b-e both afforded the corresponding secondary alcohols in better yields than benzaldehyde (2a). The reaction of ethyl(4-methoxyphenyl)silanediol (1) with various aromatic aldehydes also resulted in giving good yields. In addition to arylsilanediols, the use of alkenylsilanediol 4 afforded the corresponding allylic alcohol in 79% yield. On the other hand, the reaction with aliphatic aldehydes (2h) was found to be unsuccessful.Oi and Inoue recently reported that aryldifluorosilanes also reacted with aldehyd...