Coupling of alkenylstannanes

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]. 

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. 

This alternative to the Friedel-Crafts reaction, extensively developed by Stille and coworkers, is particularly important, since the reaction conditions are essentially neutral, and so provides a method for acylation of compounds containing an acid-sensitive functionality which would preclude the use of the Friedel-Crafts reaction. Reaction temperatures are often below 100 C, and high (1000-fold) turnovers of the catalyst have been achieved. Solvents employed include chloroform, toluene, and, on occasions, HMPA. Some reactions have been carried out under an atmosphere of carbon monoxide to prevent excessive decarbonylation of the acyl palladium intermediate. Indeed, carbonylative coupling of alkenylstannanes with allyl halides in the presence of carbon monoxide ca. 3 atm or greater 1 atm =101 kPa) offers an alternative to the Friedel-Crafts acylation, ketones being formed by the reaction of the stannane with the acyl species formed by carbon monoxide insertion into the allyl palladium intermediate. ... 

Acylations. 2-Alkynoic esters arc the presence of (PhaP>4Pd and ba.se i DM Stille coupling. The usefulness preparation of arylcoumarin inhibitors < readily obtained from RSnBu, and brom The Stille coupling is accelerated b congested substrates has been developed coupling of alkenylstannanes using shgl synthesis of (—)-wodeshiol.- ... 

Useful structures arise from regioselective coupling of alkenylstannanes with benzylic bromides, that of alkynylstannanes with allenyl bromides, and hydrosilanes with alkenyl iodides. ... 

Coupling of allylic compounds. Cross-coupling of alkenylstannanes with allylic carbonates provides 1,4-dienes. Allyltriethylgermane is obtained from Et,GeSnBuj and allylic halides. ... 

Pd(0)-Catalyzed Reactions of sp Organic Halides and Pseudohalides 3.6.3.3 Coupling of Alkenylstannanes... 

TABLE 12. Pd-Catalyzed Cross-Coupling of Alkenylstannanes with Allylstannanes... 

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]. 

Coupling of aryl halides with alkenyl stannanes promoted through palladium metal catalysis, otherwise known as the Stille coupling, has many applications,22 including solid-phase variants (see Chapter 2).3-5 One of these is featured in Nicolaou and co-workers solid-phase synthesis of (5)-zearalenone wherein a resin-bound alkenylstannane undergoes a Stille cycli-... 

The palladium/copper-cocatalyzed coupling of the readily available trisubsti-tuted alkenyl(phenyl)iodonium triflates 77 with alkynyl- and alkenylstannanes proceeds under exceedingly mild conditions with retention of geometry of the alkenyl ligand of the iodonium salt (Scheme 35) [60]. 

The construction of the highly functionalized cyclic polyether framework 339 in maitotoxin has been achieved by efficient coupling of the alkenylstannane 338 with the enol triflate 337 [159]. The smooth coupling occurs in the presence of CuCl (2 equivalents) and K2CO3 in THF. 

Figure 2.1.10 76.4 MHz " Snp H NMR spectrum of a mixture of isomers of alkenylstannanes, in which a boryl group is either in cis- or in trans-position relative to the stannyl group. The line widths of the " Sn NMR signals are a function of the residual broadening owing to partial relaxation of three-bond " Sn— 6 spin-spin coupling. ...

The stereospecific Stille coupling of alkenyl bromides or iodides with alkenylstannanes is one of the most widely applied methods for the synthesis of dienes. Thus, a slight modification of the original method was applied in the coupling of alkenyl iodide 1 with (Z)-alkenylstannane 2, stereospecifically building a polyene as the last step in the synthesis of (—)-stipiamide (Scheme 5.4.1).25... 

Panek reported the syntheses of the anti-fnngal agents cystothiazoles A (100a) and B (101) from non-symmetrical bisthiazoles 98a,b, which were prepared by the regioselective coupling of bistriflate 96 with stannanes 97a,b (Scheme 5.4.19).This synthesis also made nse of a second Stille coupling of 98a,b with alkenylstannane 99. 

The coupling of benzyl halides with stannanes has been occasionally used in synthesis.One illustrative example is the total syntheses of piericidin A1 (119) and B1 (120).i2o in these syntheses a heterobenzylic Stille cross-coupling reaction of 116 with alkenylstannane 117 proceeded in the presence of a Pd(0) complex bearing bulky PrBuj as the ligand to give key intermediate 118 (Scheme 5.4.23). 

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