Indium reagent

These mesylates, in turn, can be converted to enantioenriched allenyltin, zinc, and indium reagents which add to aldehydes with excellent diastereo-and enantioselectivity to afford either syn- or anti-homopropargylic alcohols or allenylcarbinols (eq 2, 3, and 4).3 4 Adducts of this type serve as useful intermediates for the synthesis of polyketide and hydrofuran natural products.5... 

Allenic alcohols couple with allyl indium reagents at 140°C to give allylic alcohol products. Similarly, (o-hydroxy lactones couple with organoindium reagents. 

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

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... 

Addition of the indium reagent derived from the foregoing (P)-allenylstannane to /8-benzyloxy-a-methylpropanal as the aldehyde substrate at low temperature afforded a 70 30 mixture of anti,anti and anti,syn adducts (Eq. 9.141). The improved dia-stereoselectivity in this case can be attributed to substrate control, reflecting the chelating ability of an OBn versus an ODPS group. The lower temperature may also account for the improved diasteroselectivity. 

Scheme 9.36 Transition states for additions of allenyl indium reagents to a-oxygenated aldehydes.

For the gem-diallylation of anhydrides, with an indium reagent, see Araki Katsumura lto Butsugan Tetrahedron Lett. 1989, 30, 1581. 

A large part of organoindium chemistry so far reported deals with reactions of allylic and propargylic indium reagents. These are summarized in Sections 9.14.3.1-9.14.3.9. Reactions of other type of organoindium compounds are overviewed in Sections 9.14.3.10-9.14.3.14. 

The control of diastereoselectivity in the allylation reaction of carbonyl compounds with allylic indium reagents has been an important issue since the discovery of the indium-mediated carbonyl allylation. As earlier discussions have been summarized in the precedent reviews,6-24 only relatively recent references are cited below. 

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... 

Triorganogallium and -indium reagents react with a,/3-unsaturated nitrile, ketone, and ester to give 1,4-addition products regioselectively (Table 31). In contrast, the reaction of allylgallium and allylindium sesquihalides with a,/3-unsaturated carbonyl compounds proceed in a 1,2-addition mode, whereas 1,4-addition takes place with a,/3-unsaturated nitriles.294... 

HEU-VOLHARDT ZEUNSKI Bromination 163 HENBEST Indium reagent 164 HENRY Ntlrocondansatton 16S Hspp 124... 

Preparation and Addition Reactions of Allylic and Allenic Tin and Indium Reagents... 

The high anti selectivity observed in these additions with both branched and unbranched aldehydes makes the oxygenated allylic indium reagents well suited for applications related to annonaceous acetogenins [74]. The following examples are illustrative (Eqs 55-58). 

A possible explanation might lie in the experimentally determined relatively poor reactivity of enals, compared with ynals, toward these allylic indium reagents. The slower rate of addition would enable equilibration of the kinetic (E) allylic indium intermediate to a mixture of E) and (Z) isomers. The latter would afford the syn adduct. 

Marshall, J. A. Preparation and addition reactions of allylic and allenic tin and indium reagents. Lewis Acids in Organic Synthesis 2000,1, 453-522. 

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