Arylstannanes preparation

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]. 

Ketones can be prepared by trapping (transmetallation) the acyl palladium intermediate 402 with organometallic reagents. The allylic chloride 400 is car-bonylated to give the mixed diallylic ketone 403 in the presence of allyltri-butylstannane (401) in moderate yields[256]. Alkenyl- and arylstannanes are also used for ketone synthesis from allylic chlorides[257,258]. Total syntheses of dendrolasin (404)f258] and manoalide[259] have been carried out employing this reaction. Similarly, formation of the ketone 406 takes place with the alkylzinc reagent 405[260],... 

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

Innumerable aryl- and heteroarylstannanes take part in Stille couplings with halopyridines. In one such example, the union of arylstannane 106 and 4-bromopyridine furnished arylpyridine 107 [90], Arylstannane 106 was prepared from the Pd-catalyzed reaction of hexabutylditin with iodoarene 105, which arose from aminobenzolactam 104 via a Sandmeyer reaction. 

Triorganostannyl anions are excellent nucleophiles in SrnI processes with aromatic substrates,86 and arylstannanes can be prepared from the photostimulated reactions of Ph3SnNa or Me3SnNa (from R3SnCl + Na) and aryl halides in DMSO, or of aryl amines, via their ammonium salts,88 in liquid ammonia, or of phenols, via their phosphates, in liquid ammonia.89 Examples are given in Equations (11)—(13). 

Stille cross-coupling and reductive N-heteroannulation steps. lodination of 1033, followed by Stille cross-coupling of the corresponding iodo derivative 1034 with the arylstannane 1035, gave the annotation precursor 1036. Reductive N-heteroannula-tion of 1036 afforded the carbazolone 1001, which was previously (99) (see Scheme 5.143) used to prepare clausenalene (90) via a Wolff-Kishner reduction followed by aromatization (659) (Scheme 5.155). 

Another major route for synthesis of stannanes is reaction of an organometallic reagent with a trisubstituted halostannane. This is the normal route for preparation of arylstannanes. 

Support-bound stannanes have been prepared from phenyllithium bound to macro-porous polystyrene and chlorostannanes [14,41], by treatment of support-bound alkyl chlorides with lithiated stannanes [21,41], and by radical or palladium-mediated addition of stannanes to alkenes and alkynes (Figure 4.7 [42-47]). The chloride of poly-styrene-bound chlorostannanes can be displaced by treatment with arylzinc reagents, thereby yielding resin-bound arylstannanes [46]. Polystyrene-bound stannanes have also been prepared by copolymerization of 4-[2-(dibutylchlorostannyl)ethyl]styrene with styrene and divinylstyrene [48],... 

Aryl ketones can also be prepared by C-acylation of support-bound arylstannanes with acyl halides (Entry 4, Table 12.1). The reaction conditions are mild and suitable for selective chemical transformations of polystyrene-bound intermediates. As an alternative, resin-bound arylstannanes can be converted into benzophenones by treatment with aryl halides and carbon monoxide ([(Pd(PPh3)4], DMSO, 80 °C, 18 h-3 d [8]). 

Coupling of an aryl triflate with an arylstannane is a good mediod for the preparation of biaryls and other bis-aromatic species of all types. Coupling of vinyl groups takes place with retention of stereochemistry. Furdiermore transfer of die allyl group occurs smoothly. 

In the presence of a catalytic amount of PdCh, Ar>,BiX2 (X=C1, OAc) couples with arylstannanes to give biaryls (Scheme 14.155) or, under a CO atmosphere, diaryl ketones (Scheme 14.156) [316]. Unsymmetrical biaryls are also prepared by Pd-catalyzed reaction of diaryliodonium salts with Ar3BiX2 [317]. Terminal acetylenes are phenylated by Ph3BiF2 under CuCl catalysis to afford phenyl-substituted acetylenes [318]. 

The first application of arylstannanes was presented by Stille who demonstrated the transferability of an aryl group from tetraphenyltin [50]. This approach was generalised by the improved preparation of arylstannanes from trialkylstannanes and aryl halides followed by their Pd(0) catalysed coupling with aryl halides [51]. Similarly to aryl halides, aryl triflates also react with arylstannates to give biphenyls [52]. Electron-rich aryl triflates are especially suitable coupling reagents in the synthesis of unsymmetrical biaryls [53]. Symmetrical biaryls can be easily obtained by the reaction of an aryl triflate with 0.5 eg. of hexamethyldistannane. 

N-Tosylbenzamides. These compounds are prepared from arylstannanes and TsNCO under Friedel-Crafts reaction conditions. 

Numerous methods for the preparation of symmetrical and unsymmetrical diaryl- and hetaryliodo-nium organosulfonates have been developed. A common synthetic approach to unsymmetric diaryl-and hetaryl(aryl)iodonium tosylates (e.g 262, 264, 266 and 268) is based on the reactions of [hydroxy(tosyloxy)iodo]arenes with aryltrimethylsilanes 261 [198], aryltributylstannanes 263 [376], aryl-boronic acids 265 [377], or the appropriate heteroaromatic precursors 267 (Scheme 2.75) [378,379]. The reaction of HTIB with arylstannanes proceeds under milder conditions compared to arylsilanes and is applicable to a wide range of arenes with electron-withdrawing substituents. Arylboronic acids in general have some advantage over arylstannanes in the case of the electron-rich heterocyclic precursors [377]. 

Tin Reagents. The Af-protected triflyloxy derivative 41 of pyrrolo[2,3-d]pyrimidine when reacted with an arylstannane affords 5-aryl derivatives (Scheme 20). A closely related reaction has been used in the preparation of the 5-substituted ]S-2 -deoxyribo-sylpyrrolo[2,3-[Pg.423]

These types of coupling procedures, though useful, may be limited by the availability of the requisite stannane. A promising solution to this problem involves reaction of readily available allylic acetates with aryl halides in the presence of hexa-n-butyl-distannane (Bu SnSnEu ). This avoids the need to prepare the previously used substrate, the arylstannane, and it will be interesting to see whether this technique becomes applicable to processes such as those shown in Scheme 53-... 

The Sn-NMR chemical shifts of the poly(alkyl-) and poly(arylstannanes), surprisingly, are quite similar the cyclic products have up field chemical shifts (Table 8.1). In contrast to the fairly linear polystannanes prepared by the catalytic action of zirconocene catalysts, branched polymers are obtained in the reaction of Bu2SnH2 with the rho-... 

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