Organostannanes 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]. 

Arenediazonium salts are also used for the couplina[563], (Z)-Stilbene was obtained unexpectedly by the reaction of the ti-stannylstyrene 694 by addition-elimination. This is a good preparative method for cu-stilbene[564]. The rather inactive aryl chloride 695 can be used for coupling with organostannanes by the coordination of Cr(CO)3 on aromatic rings[3.565]. 

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]. 

Coleman established the hydroxypropyl stereochemistry via addition of a homochiral a-alkoxyalkyl organometallic species. This reagent was prepared in high enantiomeric excess using a Noroyi BINAL-H reduction of organostannane 33, which was transmetallated with ra-BuLi to achieve the desired organolithium reagent 35 (Scheme 7.5). Both enantiomers of 35 could be obtained via this route. 

The main method for the preparation of different types of organostannanes is the ancient Wilrtz reaction between triorganotin halides or diorganotindihalides. Reactions proceed with or without solvent. Usual solvents are benzene, toluene, xylene, diethyl ether and ethanol. Occasionally hquid ammonia is also used. The preferred metals for this reaction are sodium and lithium. In the case of triorganotin halides, the reaction leads to symmetric hexaorganoditin compounds72 ... 

Unsymmetric organostannanes can be prepared by the reaction of triorganotin sodium compounds in hquid ammonia with a triorganotin halide73,74 ... 

Like most aryl halides, furyl halides and furyl triflates have been coupled with a variety of organostannanes including alkenyl, aryl, and heteroaryl stannanes in the presence of catalytic palladium. Carbamoylstannane 66 was prepared by treating lithiated piperidine with carbon monoxide and tributyltin chloride sequentially. The Stille reaction of 66 and 3-bromofuran then gave rise to amide 67 [61]. In another example, lithiation of 4,4-dimethyl-2-oxazoline followed by quenching with MesSnCl resulted in 2-(tributylstannyl)-4,4-dimethyl-2-oxazoline (68) in 70-80% yield [62], Subsequent Stille reaction of 68 with 3-bromofuran afforded 2-(3 -furyl)-4,4-dimethyl-2-oxazoline (69). 

The Diels-Alder reaction has also been used to prepare special reagents. Thomas and coworkers80, for instance, studied the Diels-Alder reactions of methyl (E)- and (Z)-3-(triphenylstannyl)acrylates 72a and 72b with cyclopentadiene and converted the organostannanes obtained to tin hydrides. (E)-72a afforded endo 73 exclusively with 99% yield, whereas (Z)-72b afforded a 2 1 mixture of endo 74 and exo 75 with 77% overall yield (equation 24). Cycloadduct 73 was easily converted to tin hydride 76. By... 

We note that while tin reagents have often been employed for the organoboron halides/ the use of organostannanes as starting materials can also be applied to the synthesis of heavier group 13 derivatives. In the context of polyfunc-tional Lewis acid chemistry, this type of reaction has been employed for the preparation of ort/ o-phenylene aluminum derivatives. Thus, the reaction of 1,2-bis(trimethylstannyl)benzene 7 with dimethylaluminum chloride, methylaluminum dichloride or aluminum trichloride affords l,2-bis(dimethylaluminum)phenylene 37, l,2-bis(chloro(methyl)aluminum)phenylene 38 and 1,2-bis(dichloroalumi-num)phenylene 39, respectively (Scheme 16). Unfortunately, these compounds could not be crystallized and their identities have been inferred from NMR data only. In the case of 39, the aluminum derivative could not be separated from trimethyltin chloride with which it reportedly forms a polymeric ion pair consisting of trimethylstannyl cations and bis(trichloroaluminate) anions 40. 

Barrett and Kohrt" ° and Kelly and Lang" independently reported the first examples of oxazole triflates (Scheme 6.17). In both cases, the requisite 2-aryl-4(5/7)-oxazolone, 56 or 59, was treated with trifluoromethanesulfonic anhydride (Tf20) to afford 60a or 60b, respectively, which were then coupled successfully with a variety of organostannanes. Kelly and Lang" attempted to extend this methodology to prepare the key oxazole triflates 63 in their approach to sulfomycin I. However, they were unexpectedly thwarted when 61 could not be cyclized to the requisite 4(57/)-oxazolone precursors 62. Schaus and Panek described an unproved procedure to prepare 56 in 90% yield very recently. 

In 2003, Fairlamb and co-workers reported on the synthesis of complex 57 as a novel catalyst for Stille reactions. The complex is prepared in one step from Pd2dba3-GHGl3, PPh3, and A-bromosuccinimide, and catalyzes the coupling of allylic and benzylic bromides with a variety of organostannanes in toluene at 60 °G. 

The acylpalladium is formed by CO insertion as the intermediate of the carbonylation. They can be prepared directly by the oxidative addition of acyl chlorides to Pd(0). Thus ketones can be prepared by the reaction of acyl halides with organozinc reagents and organostannanes. Benzoacetate (490) is obtained by the reaction of benzoyl chloride with the Reformatsky reagent 489 [243], The macrocyclic keto lactone 492 is obtained by intramolecular reaction of the alkenylstannane with acyl chloride in 491 [244]. 

Cellulose can be modified with organostannane chlorides, such as dibutyl or triphenyl derivatives [91,92], or with organotin halides in the presence of bisethylenediamine copper(II) hydroxide [93]. Epoxy-activated cellulose was prepared by reacting cellulose acetate fibers with sodium methoxide, followed by reacting it with epichlorohydrin in DMSO. This epoxy-activated cellulose has proved to be a useful intermediate to react with substances containing active hydrogen, such as amine, amino acid, or carboxylic acids [94], as shown in Fig. 3. Epoxidized cellulose has also been converted to a thiol derivative via reduction of a thiosulfate intermediate [95], and sulfoethylcellu-[ose has been obtained from sodium chloroethanesulfonate [96]. Cellulose... 

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