Alkynyl stannanes

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

Reaction of (diisopropylamino)chloroboryl ethers of alkynols (57) with alkynyl-stannanes (58) in the presence of nickel catalysts has been reported to afford formal f/ms-alkynylboration products (60), which could undergo the Suzuki-Miyaura coupling with organic halides. The 2-borylalkenylnickel(II) complex (59) was isolated as an intermediate in a reaction of the chloroboryl ether (57) with 1 equiv. of a nickel(0)-phosphine complex and characterized by X-ray crystallography.61... 

Dioxa-, oxathia-, and dithiaboroles undergo efficient transmetallation with alkynyl stannanes, furnishing the 5-alkynyl boroles. Thus the reaction of bis(trimethylstannyl) acetylene 273 with 2 equiv of bromoboranes 272 in toluene at room temperature furnishes air-sensitive boroles 274 as colorless solids in good yield (Equation 10) <2004EJI4223>. 

The hypervalent tin compound 350 reacts with the strong base lithium diethylamide leading to the elimination of chloride and subsequent coordination between B-N-Sn to form azoniastannaboratole derivative 351 (Equation 18) <2003JOM188>. The starting materials (m-borylstannanes 350) can be obtained by the organoboration of alkynyl-stannanes stereoselectively. 

Other related species, such as alkyl chloroformates183, dialkyl carbamyl chlorides1, 77-aryl iminoyl chlorides184 or N-substituted isocyanide dichloride (with alkynyl stannanes only)185 behave in an analogous manner. Acylation of acid chlorides has even proven to be possible with acyltin reagents, or by dimerization of acid chlorides with hexabutylditin and high CO pressure186. 

The Stille reaction, which represents over half of all current cross-coupling reactioi has been used in total synthesis with excellent results. The reaction may also be carried o intramolecularly and with alkynyl stannanes instead of the more usual aryl or vinyl stannan even to form medium-sized rings. This example forms a ten-membered ring containing t alkynes. 

Interesting coupling reactions can be earned out with alkenyl- and alkynyl-stannanes. Reductive eoupling of aeid ehlorides with ( )-l,2-bis(tri-n-butylstannyl)-... 

Carbostannation of alkynes, and 1,2- and 1,3-dienes can be brought about by acyl, allyl, or alkynyl-stannanes in the presence of a nickel(O) catalyst. ... 

SEM and -THP-protected pyrazole-5-boronates are easily prepared via direct lithiation and undergo cross couplings under standard conditions." Pyrazole-5/3-stannanes (with no M-protection) can be prepared by ring synthesis from alkynyl stannanes. The example shown below, bearing a 4-fluorine, requires iodo-arenes as substrates for cross coupling."" ... 

Propargylic alcohols When catalyzed by Me2AlCl, the addition of alkynyl-stannanes to aldehydes is subject to chelation control by a (3-alkoxy or siloxy group in the substrate. 

Coupling of alkenyl- or alkynyl-stannanes with alkenyl(phenyl)iodonium triflates leads to stereodefined dienes or enynes. ... 

The great majority of o-acetylide transition metal complexes are prepared by interaction of a metal halide with acetylide, RC C", or the formal oxidative addition of terminal alkynes or alkynyl stannanes to the metal center. As amply demonstrated in the previous section, alkynyliodonium salts may serve as electrophilic acetylene equivalents. In other words, transition metal complexes may act as nucleophiles in reactions with alkynyliodonium species. Indeed, the reaction [81] of the square planar Vaska s complex, 106, and its Rh analog, 107, with a variety of alkynyliodonium triflates in toluene results in 89-96% isolated yield of the hexa-coordinate o-acetylide complexes, 108 and 109 [Eq. (58)]. Reaction is essentially instantaneous and occurs with retention of stereochemistry around the metal center. 

Corey and Cimprich have used acetylenic dimethylborane as the nucleophile for the asymmetric addition of acetylenic nucleophiles to aldehydes. This reagent was generated in sitn from the corresponding alkynyl stannane and bromodimethylborane (Scheme 21.12). A typical procedure involved addition of a solution of bromodimethyl-borane in methylcyclohexane to a solution of the alkynyl stannane (1.3 to 1.5) in toluene at -78°C. A solntion of the oxazaborolidine (0.25 to 1 equiv in toluene) was added after 30 minntes, and after an additional 15 minntes the aldehyde was added. The chiral... 

A four-component coupling between benzyl halides and alkynyl stannanes has been developed for the preparation of functionalized enynes. Activated olefins participate in a regioselec-tive Pd(dba)2-catalyzed three-component coupling with allylic acetates and BusSnH. Allylic amines have been prepared via reaction of vinyl halides, alkenes, and amines in the presence of Pd(dba)2 and BU4NCI. Organogermanes and silanes have been constructed via multicomponent carbogermanylation and carbosilylation sequences. 

Nickel-catalyzed Carbostannylation. When 3-trimethylsilyl-1 -propyne is subjected to a 1,2-diene in the presence of an alkynyl-stannane and a nickel catalyst, a carbostannylation takes place with high Z-selectivity under the specified conditions. Alternative conditions provided the -isomer as the major product (eq 43). ... 

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