Alkenylstannane

The reaction of alkenyl iodides or triflates, alkenylstannanes, and CO affords divinyl ketones[397,398]. Thus the capnellene skeleton 538 has been synthesized by the carbonylation of the cyclopentenyl triflate 536 with the alkenyltin 537[392], The macrocyclic divinyl ketone 540 has been prepared in a moderate yield by the carbonylative cyclization of 539[399]. 

Aryl halides react with a wide variety of aryl-, alkenyl- and alkylstan-nanes[548-550]. Coupling of an aryl tritlate with an arylstannane is a good preparative method for diaryls such as 688. The coupling of alkenylstannanes with alkenyl halides proceeds stereospecifically to give conjugated dienes 689. The allylstannane 690 is used for allylation[397,546,551-553]. Aryl and enol triflates react with organostannanes smoothly in the presence of LiCl[554]. 

The intramolecular coupling of organostannanes is applied to macrolide synthesis. In the zearalenone synthesis, no cyclization was observed between arylstannane and alkenyl iodide. However, intramolecular coupling take.s place between the alkenylstannane and aryl iodide in 706. A similar cyclization is possible by the reaction of the alkenylstannane 707 with enol triflate[579]. The coupling was applied to the preparation of the bicyclic 1,3-diene system 708[580]. 

Alkenylation of cyclopentenone with the alkenylstannane 719 has been used for the introduction of an a,>-chain into a prostaglandin derivative[590]. Even the vinyl mesylate (methanesulfonate) 720 can be used for coupling with alkenylstannanes[59l]. 

The intramolecular insertion of an internal alkyne into an aryl or alkenyl halide 727 generates aryl- or alkenylpalladium as an intermediate, which is trapped with an organozinc or organostannane to give 728. Overall cis addition to the alkyne takes place[595,596]. The reaction of the alkenylstannane 730 with the 2-bromomethylfuran 729 is used for the introduction of a prenyl group[597]. 

Sulfonyl chloride reacts with an alkenylstannane to give the alkenylsulfone 882[752]. 

Transmetalalions of alkenylstannanes with copper sails are reversible if they ate perfotcned witli CuCl in polar solvents [101], Tliis has found application in cycli-zahon reactions fScheme 2.49) [102],... 

Alkenylstannanes react with 1,1-dibromoalkenes to give enynes.204 These reactions are thought to involve elimination of the elements of HBr prior to reductive elimination. 

Lewis acid-catalyzed hydrostannylation has been observed using ZrCl4. With terminal alkynes the Z-alkenylstannane is formed.142 These reactions are probably similar in mechanism to Lewis acid-catalyzed additions of silanes (see p. 811). 

Addition of tri-n-butylstannyllithium to aldehydes followed by iodination and dehydro-halogenation gives primarily Zs-alkenylstannanes.155... 

Using the olefination reactions mediated by CrCl2137, Hodgson prepared E-alkenylstannanes of the type 57138 ... 

Oxidative coupling of alkenylstannanes.3 1-Alkenylstannanes undergo homocoupling to 1,3-dienes when treated with f-butyl hydroperoxide in the presence of catalytic amounts of Pd(OAc)2. Under these conditions 1-alkenylstannanes couple with 2-aIkenyIstannanes to give 1,4-dienes. 

Tributyl-l, 1 -diiodomethylstannanes react with aldehydes in the presence of CrCl2 to give -alkenylstannanes. 

Alkenylstannanes are usually reported to be resistant to hydrogenation with typical metal catalysts, though a rhodium(l) catalyst has been used at 100atm to reduce 3-hydroxy-l-alkenylstannanes.220 Diimine has been used to reduce some acyclic and cyclic methylstannylalkene compounds, but lower yields were obtained with tributylstan-nylalkenes (Equation (72)).221,198... 

The stannacyclopentadienes (stannoles) can be regarded as a special group of alkenylstannanes. In the past they have been prepared by reactions similar to those which are used for acyclic alkenylstannanes, for example, by the reaction of LiPhC=CPh-CPh=CPhLi with Me2SnCl2. In recent years, however, some methods have been developed that are special to the cyclic compounds, and involve transition metal chemistry. 

The acidity of terminal alkynes makes available routes to alkynylstannanes that do not apply to alkenylstannanes. Thus, alkynylstannanes can be made by the acidolysis of aminostannanes with alkynes, and the iV-stannylpyr-roles are recommended for this purpose as they can be readily prepared by azeotropic dehydration of the trialkyltin oxide and pyrrole, and the amine that is liberated is non-basic.242... 

Addition reactions at the alkyne bonds are dealt with in the section on alkenylstannanes that are produced. The alkynyl-tin bond is more readily cleaved by both electrophiles and nucleophiles than is the alkenyl- or alkyl-tin bond. Strong electrophiles such as halogens or halogen acids attack at the z/Mzi-position of the triple bond to give a /3-stannyl cation that is stabilized by C-Sn hyperconjugation, but this is followed by cleavage of the C-Sn bond (Equation (83)). 

As well as alkenylstannanes [106-108], other classes such as a-heteroatom-substituted alkyltributylstannanes [109] and, more importantly, allylic stannanes [110, 111] also undergo these Sn-Cu transmetalations. Otherwise difficult to prepare, allylic copper reagents may, however, be obtained by treatment of allylic stannanes (produced in turn from organolithium, magnesium, or zinc organometallics) with Me2CuLi LiCN. They enter into cross-coupling reactions with alkyl bromides [110] or vinyl triflates (Scheme 2.52) [111]. 

A 1,2-metalate rearrangement of a higher order cuprate, known as a Kodenski rearrangement [64], was used as a key step in the synthesis of the marine antiinflammatory sesterterpenoid manoalide 95 (Scheme 9.20) [65]. Treatment of the alkenyl lithium 89 (prepared from the alkenylstannane 88 with s-BuLi in a diethyl ether-pentane mixture) with the homocuprate 91 (produced from iodoalkane 90) gave the iodoalkene 94 in 72% overall yield from 88. The reaction proceeds as fol-... 

One of the first cross-coupling reactions performed on solid supports was the Stille reaction [250] which is a paUadium-catalyzed reaction of a trialkylaryl or trialkylalkenyl stannane with an aromatic iodide, bromide or triflate. In contrast to the process in liquid-phase, the organotin reagent is easily removed from the solid-phase because of the subsequent washing processes. Immobilized aryl halides have been frequently coupled with aryl and alkenylstannanes, whereas stan-nanes attached to the solid support have been used less frequently for the StiUe reaction. An example is the synthesis of a benzodiazepine library by EUman et al. Recently, a Stille cross-couphng reaction has been employed in the synthesis of al-kenyldiarylmethanes (ADAM) series of non-nucleoside HlV-1 Reverse Transcriptase Inhibitors (Scheme 3.14) [251]. 

Terminal alkenylstannanes can be prepared after homologation of aldehydes via the Corey-Fuchs reaction.95... 

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