A-vinylstannane

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mcrcuration/boration, undergo coupling with vinyl triflates (Entry 10). 

Scheme 32. Stille couplings of regioselectively generated enol triflates with a vinylstannane.

Scheme 14 Pd/IPr-catalyzed coupling of aryl halides and a vinylstannane...

C-Sn Hyperconjugation in an intermediate P-stannyl radical is also important in the conjugative homolytic substitution of an allylstannane (equation 3-30)15-16 (see Section 9.1.3.3), and in the ipso substitution of a vinylstannane (equation 3-31 see Section 8.1.2). 

The most common routes to alkenyltin compounds involve reaction between an alkenyl-metallic compound and a tin halide, or the hydrostannation of an alkyne (see Section 4.4). In recent years, the stannylmetallation of alkynes has become increasingly important. Direct hydrogenation of an alkynylstannane to a vinylstannane does not appear to be practicable, presumably because the catalyst is poisoned by the tin compound, but cis addition of dihydrogen can be achieved by hydrozirconation followed by hydrolysis,1 or in some cases, by cyclotitanation followed by hydrolysis2 (Section 8.2.2 below). 

In a similar manner to alkynes, arynes accept the addition of alkynylstannanes in the presence of a catalytic amount of a palladium-iminophosphine complex (Scheme 5.7.15). Here, a characteristic feature is the participation of a vinylstannane. The usual catalytic cycle (Scheme 5.7.16, left), starting with oxidative addition of a carbon-tin bond, is possible, but rather improbable, because there are no signs of oxidative addition of alkenylstannanes that can participate in the present carbostannylation. Consequently, the palladium(O) complex is likely to undergo oxidative cyclization with an aryne to form a palladacyclopropene (Scheme 5.7.16, right), which then reacts with an organostannane. 

It is worthy of note that palladium-mediated cross-coupling between a vinyl halide and a vinylstannane has been used in synthesis of a macrolide. For access to apoptolidin a C11-C12 bond was formed by use of the Cl-Cll and C12-C28 vinyl components to give the desired C1-C28 segment (Scheme 12.91) [193]. Intramolecular coupling under the influence of palladium catalyst resulted in the formation of the desired macrolactone, which was converted to (-)-lasonolide (Scheme 12.92) [194]. 

Acid hahdes can also be used in Migita-Kosugi-Stille coupling in this C-C bond formation fhe corresponding ketone is produced. Subjection of a benzoyl chloride derivative prepared in situ to cross-couphng with a vinylstannane provided the desired vinyl ketone which was successfully transformed to a potent COX-2 inhibitor (Scheme 12.99) [201],... 

Intramolecular coupling of 120 having an aryl iodide group and a vinylstannane group accomplished the total synthesis of (-)-zealarenone (99) (Scheme 19) [77]. The first total synthesis of macrolactin A (124) was efficiently accomplished based on the Stille reaction of 122 for both stereospecific construction of the diene moieties and closure of the 24-membered macrocyclic ring [78]. The key precursor 122 was synthesized via two Stille couplings and Mitsunobu esterification. An alternative route to the dimethyl ether 125 was reported by cyclization of 123, which was prepared by the Stille and Suzuki couplings followed by DCC-DMAP esterification... 

Scheme 2.35 highlights some a — d combinations that have been used in the synthesis of 11. The most efficient method appears to be the Pd(0)-mediated coupling of an acid chloride with a vinylstannane moiety [50, 51]. 

Fluoride may be extracted from triarylbismuth difluorides to yield fluorobismuthonium salts, as shown below. A carbon nucleophile, such as an enol ether, an allylsilane, or a vinylstannane, may then displace the Bi-bound fluoride to yield a variety of exceedingly useful triarylbismuthonium intermediates. 

Scheme 6.32 Coupling of a vinylidene dibromide with a vinylstannane followed by dehydro-...

Corey and Estreicher have developed the first method for the transformation of cyclic ketones into conjugated cyclic nitro-olefins. Following conversion of the ketone into a vinylstannane via its trisyl hydrazone, the crucial step is the replacement of tin by a nitro-group at the unsaturated carbon, for which tetranitromethane in DMSO is highly effective (e.g. Scheme 36). 

The Stille-Hegedus synthesis of the diterpene jatrophone took advantage of an intramolecular carbonylative Stille coupling between a vinyl triflate and a vinylstannane motif to forge the macrocycle found in the natural product (see below). 

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