Arylstannanes formation

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... 

Pd/PCy(pyrrolidinyl)2 proved to be effective for room-temperature cross-couplings of an array of primary alkyl bromides and iodides with both vinyl- and arylstannanes (Table 6, entries 4-10). These examples establish that the desired carbon-carbon bond formation proceeds in the presence of functional groups such as cyanides (entry 5), esters (entries 5,7, and 8), and pyridines (entry 9). 

The alkyl-transfer process from tin to palladium causes the formation of methylarenes when ArSnMe, was used as the parent stannane, or K-butylarenes in the case of ArSnBu, usually in amount up to 30% [79]. Ordinarily preferential transfer of an aryl-over alkyl-group from tin to palladium became less favourable in the case of arylstannanes bearing coordinating substituents at the or//zo-benzylic positions. For example, the reaction of stannane 196 with 4-acetylphenyl triflate (197) gave the expected biaryl 198 in 50% yield, but also 4- -butylacetophenone (199) with a 24% yield [79], Scheme 30. 

During an investigation into the addition reactions of element-element o-bonds to the C—C triple bonds of arynes, Yoshida et al. observed aryne insertion into the S—Sn o-bond of stannyl sulfides (Equation 12.16) [22]. The reaction is initiated by nudeophihc attack of the sulfur atom of the stannyl sulfide on the aryne triple bond, resulhng in the formation of a zwitterion, which undergoes intramolecular nudeophihc substitution at the stannyl moiety. This affords the corresponding 2-(arylthio)arylstannane 19. 

Rhodium catalysts have been widely used for C-C bond formation processes [71], Particularly noteworthy are the Rh(I)-catalyzed additions of boronic acids and their derivatives to a.p-unsaturated carbonyl compounds [72-78] and aldehydes [75, 79] (Chapter 4). The groups of Miyaura and Hayashi have shown that Rh(I) catalyzes the addition of sodium tetraphenylborate and arylstannanes to N-sulfonylimines [80-82]. Miyaura and co-workers have also reported the first example of a Rh(I)-cat-alyzed addition of an arylboronic acid to an N-sulfonylimine (77), to give sulfonamide 78 (Equation 13) [83]. Reactions proceeded with 2 equivalents of arylboronic acids using either a cationic Rh(I) catalyst alone, or in combination with appropriate phosphine ligands such as bis(diphenylphosphino)propane or P(i-Pr)3. Boronic esters will also react, particularly in the presence of triethylamine. The reaction does not proceed with simple aldimines, such as PhCH NPh. 

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