Indiums transmetallation

Reagent-controlled stereoselectivity can provide stereochemical relationships over several centers when a combination of acyclic and chelation control and cyclic TS resulting from transmetallation is utilized. In reactions mediated by BF3 or MgBr2 the new centers are syn. Indium reagents can be used to create an anti relationship between two new chiral centers. The indium reagents are formed by transmetallation and react... 

Palladium catalyzes allylation of carbonyl compounds with various ally lie compounds using In-InCl3 in aqueous media (Eq. 8.66).158 Various allylic compounds can be effectively applied via the formation of TT-allylpalladium(II) intermediates and their transmetalation with indium in the presence of indium trichloride in aqueous media. 

A tandem enolate-arylation-allylic cyclisation, in which an essential z-butyldimethylsilyl ether protecting group delays the cyclisation step until the Pd-catalysed arylation is complete, enables 1-vinyl-l//-[2]benzopyrans 54 to be prepared from 2-bromobenzaldehyde (Scheme 32) <00CC1675>. 4-Substituted isochromans 55 are formed from aldehydes by a Pd-catalysed termolecular queuing cascade. The sequence involves cyclisation of an aryl iodide onto a proximate alkyne followed by an allene insertion. Transmetallation with indium then allows addition to the aldehyde (Scheme 33) . 

A third route to allenyltin halides involves transmetallation of isolable allenyltri-butyltin compounds, as exemplified by the reaction of allenyltributyltin with Bu2SnCl2 [68]. The resulting mixture of allenyl- and propargyldibutyltin chlorides reacts with various aldehydes to afford mixtures of propargyl- and allenylcarbinols (Eqs. 9.78 and 9.79). The yields of these additions are uniformly high, but the selectivity depends on the nature of the aldehyde substituent. The transmetallation route to allenyltin and -indium halides will be discussed in more detail in a later section. 

Homoallylic alcohols are provided by Pd-catalyzed reaction of iodobenzene, allene and aldehydes (Scheme 16.15) [19, 20]. A nucleophilic allylindium intermediate is generated through transmetallation of a Jt-allylpalladium species with indium. Such a Jt-allylpalladium complex can alternatively be provided through carbopalladation of ArPdl to a proximate acetylene followed by insertion of allene. 

A cyclic homoallylic alcohol is efficiently provided by a sequence of Jt-allylpalla-dium complex formation, transmetallation with hexa-n-butyldistannane and intramolecular allylation (Scheme 16.17) [22]. The same transformation can be conducted by means of indium (Scheme 16.18) [23]. 

Naphthalene-based bifunctional Lewis acids that involve boron and a heavier group 13 element have also been prepared starting from the boron/tin derivative 30 (Scheme 15). Thus, the transmetalation reaction of 30 with gallium trichloride or indium trichloride in tetrahydrofuran (THF) results in high yields of l-(dichlorogallium)-8-(dimesitylboron)naphthalenediyl 35 and l-(dichloroindium)-8-(dimesitylboron)... 

As for the synthesis of ort/io-phenylene indium complexes, the transmetallation reactions of organomercurials with indium(I) halides have also been considered for the preparation of 1,8-naphthalenediyl diindium complexes. While the dimercura-cycle 62 fails to react with InBr, l,8-bis(chloromercurio)naphthalene (25) and 1,8-bis(bromomercurio)naphthalene (63) react with their respective indium(I) halides to yield the mercura-indacycles 64 and 65 (Scheme 25) which have been isolated as bis(THF) adducts. The indium center of 65-(THF)2 is penta-coordinated and... 

A three-component reaction based on the umpolung of re-allylpalladium (II) complexes indium metal was reported by Grigg and co-workers (Scheme 8.31) [74]. In this reaction, the electrophilic nature of the n-allyl palladium species generated from aryl halides and allenes is reversed by transmetallation with indium metal. The resultant nucleophilic allylindium reagent subsequently adds to the third component - aldehyde [75] or imine [76] - to give the corresponding homo-allylic alcohol 64 or amine 65 respectively. 

Transmetallation of allenylpalladium species with indium salts has been previously reported Marshall, J. A. Grant, C. M. J. Org. Chem. 1999, 64, 8214-8219. 

Benzyl methyl ether or allyl methyl ethers can be selectively metalated at the benzylic/allylic position by treatment with BuLi or sBuLi in THF at -40 °C to -80 C, and the resulting organolithium compounds react with primary and secondary alkyl halides, epoxides, aldehydes, or other electrophiles to yield the expected products [187, 252, 253]. With allyl ethers mixtures of a- and y-alkylated products can result [254], but transmetalation of the lithiated allyl ethers with indium yields y-metalated enol ethers, which are attacked by electrophiles at the a position (Scheme 5.29). Ethers with ft hydrogen usually undergo rapid elimination when treated with strong bases, and cannot be readily C-alkylated (last reaction, Scheme 5.29). Metalation of benzyl ethers at room temperature can also lead to metalation of the arene [255] (Section 5.3.11) or to Wittig rearrangement [256]. Epoxides have been lithiated and silylated by treatment with sBuLi at -90 °C in the presence of a diamine and a silyl chloride [257]. 

Indium triiodide (Inl3) yields a transient allenylindium species from ( (-allenyltin with mainly retention of configuration. In contrast, transmetallation with BuSnCl3 affords an intermediate allenyl species with inverted... 

A new preparative method for allylic indium(m) reagents via a reductive transmetallation of 7r-allylpalladium(n) or 7T-allylnickel(n) complexes with indium(i) salts is reported. This method enables the use of a wide variety of allylic compounds, such as allylic chlorides, acetates, and even allylic alcohols, in combination with Pd or Ni catalysts.43-50 7r-Allylpalladium(ii) resulting from the addition of arylpalladium(n) to allene is also transformed by metallic indium to the corresponding allylindium.51-54 Similarly, propargylindium(m) can be prepared from the corresponding propargyl alcohol derivatives.55-58... 

Indium trichloride-mediated addition of (i )-a-(methoxymethoxy)allylic stannane (>95% ee) to cyclohexanecarbox-aldehyde affords the anti-adduct predominantly (anti syn = 98 2) and stereoselectively (>95%ee) (Equation (12)). Production of a transient allylic indium reagent is postulated via a stereosepecific anti-Se2 transmetallation. This a-(methoxymethoxy)allylic stannane reacts without allylic inversion, whereas the reaction of crotylstannane in Equation (5) (Section 9.14.3.3.1) proceeds with net allylic inversion. <5-Oxygenated allylic stannane also undergoes transmetallation with InCl3, and in situ addition to a-ODPS acetaldehyde leads mainly to the //-adduct, which is a potential precursor to D-(+)-altrose (Scheme 31).149,150... 

Allylindium, generated by transmetallation of 5-benzyloxy-4-methyl-2-pentenyl(tributyl)stannane, reacts with benzaldehyde leading to the l,5-< /z//-CE)-stereoisomer with a useful level of 1,5-stereoinduction (Equation (13)).151 2-C-branched sugars and C-disaccharides are prepared diastereoselectively by the indium-mediated reaction of 4-bromo-2-enpyranoside (Equation (14)).152... 

Indium enolates, prepared conveniently via transmetallation of lithium enolates with InCl3, react with aldehydes to give the corresponding /3-hydroxy esters (Table 20).325... 

Allylgallium sesquibromides can be prepared from allylic bromides and metallic gallium in the presence of a catalytic amount of indium, where the initially formed allylindium is converted to allylgallium. Fast transmetallation of an allyl group from indium to gallium accelerates the formation of allylgallium sesquibromide (Scheme 122). ... 

The transmetalation of organotin derivatives to their indium counterparts (Scheme 1) has recently been used to investigate a new route to Group 13 polyfunctional Lewis acids, which are becoming important in catalysis, molecular recognition, and materials synthesis. ... 

The generation of allylic indium reagents by transmetallation of allylic stannanes with InCl3 and subsequent reaction of these with aldehydes represents an important advance for diastereoselective synthesis of homoallylic alcohols [203]. In these reactions, the stannane is added to a premixed solution of the aldehyde and InCl3 in acetone. In this way, the reaetion of cyclohexanecarboxaldehyde with the 2-butenylindium reagent affords a 98/2 antilsyn mixture of homoallylic alcohols (Scheme 10-104). 

A highly stereoselective synthesis of trifluoromethylated homoallylic alcohols is possible using the transmetallation [Sn(II) to In(IIl)] pathway [205], The indium trichloride/tin-promoted reaction of trifluorobromobutene with various aldehydes afforded the homoallylic alcohols in extremely high yield and diastereos-electivity (Scheme 10-105). The strong preference for the anti products with the simple aldehydes is expected on the basis of previous observations with 2-buteny-lindium reagents explained by the cyclic transition structure xxxiv shown. The syn homoallylic alcohol was obtained upon reaction of glyoxylic acid and 2-pyri-dinyl carboxaldehyde. The syn products were proposed to arise by reaction via the 5-membered chelate transition structures xxxv and xxxvi. 

The preparation of allenylindium reagents and their reaction with aldehydes has further expanded the utility of indium in synthesis. By making use of the transmetallation protocol, enantiomerically enriched allenyltin reagents 308 (themselves generated by an anti Sn2 substitution of propargylic mesylate 307 with... 

Transmetallation reactions between allyltin compounds and other Lewis acid metal halides (e.g. Bu2SnCl2, BCI3, BBr AICI3, or TiCU) are similarly very fast,39 and the reaction between allyltriphenyltin and BCI3 (though not BF3-OEt2) is complete within one second.40 Reactions of this type have been used for preparing allylic derivatives of boron,41,42 indium,10,38 copper 43 phosphorus, arsenic, antimony,44 and other metals. 

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