Allylation indium-promoted

C-branched sugars or C-oligosaccharides are obtainable through indium-promoted Barbier-type allylations in aqueous media.151 Indium-mediated allylation of a-chlorocarbonyl compounds with various allyl bromides in aqueous media gave the corresponding homoallylic chlorohydrins, which could be transformed into the corresponding epoxides in the presence of a base (Eq. 8.62).152... 

Extension of this reaction toward a one-pot asymmetric Mannich-hydrocyanation reaction sequence was also reported by the Barbas group [29]. In this one-pot two-step process proline-catalyzed asymmetric Mannich reaction of unmodified aldehydes with the a-imino glyoxylate was performed first, then diastereoselective in situ cyanation. The resulting /i-cyanohydroxymethyl a-amino acids were obtained with high enantioselectivity (93-99% ee) [29]. Another one-pot two-step reaction developed by Barbas et al. is the Mannich-allylation reaction in which the proline-catalyzed Mannich reaction is combined with an indium-promoted allylation [30], This one-pot synthesis was conducted in aqueous media and is the first example of a direct organocatalytic Mannich reaction in aqueous media [28, 30]. 

The most widely used preparative method of allylindium(m) or propargylindium(lll) compounds is the oxidative addition of metallic indium or indium(l) halides to allylic or propargyl substrates.4 26 27 Allylic bromides and iodides serve as good allylic sources without any other activation. In the case of allylic chlorides, a proper additive such as lithium iodide is required to promote the oxidative addition. Allylic indium compounds prepared by oxidative addition of metallic indium are considered to exist as the sesquihalide structure (allyl jImXj), which has been... 

The effect of proximal groups on the diastereoselectivity in the addition of allylindium to a carbonyl group has been extensively surveyed.153 When a- and /3-hydroxy aldehydes are subjected to the allylation, excellent diastereocontrol is realized, syn- 1,2-Diol and anti- 1,3-diol products are formed, respectively, at accelerated rates (Tables 1 and 2). Protection of the free hydroxy group results in the alternative formation of 1,2-anti products. High stereoselectivities have been observed for indium-promoted allylations of a- and /3-hydroxy aldehydes in aqueous media, implying that a chelate control still operates even in water.72,73,154-158... 

A one-pot Mannich/indium-promoted allylation sequence affords highly functionalized lactones with 73% and >99% ee as a mixture of two diastereomers. There is no significant asymmetric induction for the allylation step (Equation (24)).192... 

Indium-promoted cyclization of 55 affords 2-vinylcyclohexanol 56 in 32% yield as a single stereoisomer. The configuration has tentatively been assigned as trans (Equation (34)).211 The intramolecular allylation of 57 gives chromane 58 as a mixture of cis- and trans- isomers (Equation (35)).212... 

Oxime ethers derived from 2-pyridinecarboxaldehyde and glyoxylic acid can be allylated effectively in water with functionalized allylic bromides promoted by indium (Scheme 67). When the metal is positioned in close proximity to flanking heteroatomic centers, chelation by indium is operative and affects both reactivity and stereochemistry... 

Canac, Y, Levoirier, E, Lubineau, A, New access to C-branched sugars and C-disaccharides under indium promoted Barbier-type allylations in aqueous media, J. Org. Chem., 66, 3206-3210, 2001. 

Lubineau reported a series of research works on the preparation of C-branched monosaccharides and C-disaccharides under indium promoted Barbier-type allylation in aqueous media [49]. In the case of substrate 97, the reaction, which took place in H20/Et0H (1 2) at 50 °C, gave unique stereoisomer 98 with complete regio- and diastereoselectivity. From... 

Allyl transfer to alkynes and 1,4-dienes from 1-alkynes and ally in THF at room temperature.. M similar reaction (water is present 1 Allylation of carbonyl compe and tin in promoting allylation of scope of the indium-promoted all of both reacting components, t intermediates. Allylation of unp selection to furnish 5yn-1.2-anu witnessed. ... 

Butenylcyclopropanes. The indium-promoted reaction of enones with allyl bromide gives cyclopropane derivatives in which two C3H5 units are unified to effect reductive gem-di alkylation of the carbonyl group of the enones, when the initial adducts are treated with LiBr before workup. Otherwise the normal allylation products prevail. 

Achiral allylic indium reagents and chiral aldehydes. Allylindium reagents generated in water react smoothly with aldehydes and ketones (Scheme 10-99) [196], The reaction of achiral aldehydes and a-oxygenated aldehydes 290 with the allyl indium reagents proceeds smoothly to homoallylic alcohols without the need for external promoters. It is interesting to note that the a-hydroxyl aldehyde was se-leetive for the syn (chelation-eontrolled) product even in water. 

The 1,4-asymmetric induction in the indium-promoted coupling reaction of aldehydes to protected and unprotected 3-substituted 3-oxy-bromomethylidenepropanes has been investigated [200]. The highest selectivity was observed in reactions of the silyl-protected bromomethylvinyl alkanols. A representative series is shown below in Scheme 10-102. The free hydroxyl and the methyl ether containing allylic bromides were less selective than the corresponding silyl derivative [201],... 

The indium-promoted allylation of carbonyl compounds in the presence of cinchona alkaloids (2 equiv), as a route to chiral allylic alcohols, was recently reported by Loh [20, 21]. The reaction is applicable to a variety of aldehydes and ketones. The enantioselectivities obtained with allyl bromides as the substrate are at the best moderate (up to 75% ee) [20]. However, the use of prenyl bromides as substrates... 

Indium-promoted addition of methyl (2)-2-(bromomethyl)-2-butenoate to a-pro-tected hydroxy aldehydes in water results in the formation of diastereomer 2 selectively via a Felkin-Anh transition state (Tab. 8.4) [28]. Diastereoselective allylation of a-ketoimides derived from Oppolzer s sultam proceeds in aqueous THF (Scheme 8.11) [29]. 

Indium trichloride in water catalyzed the conversion of dihydrofuran to the corresponding lactol, which was an intermediate in an indium-promoted allylation with various allylic bromides to provide 1,4-diols. The reaction with ally bromide is shown in the following scheme <04SL829>. 

Table III. Indium-Promoted C-Allylations of p-Oxygenated Aldehydes in Various Solvents at 25 C. 

Building on their work reported since 1996 describing investigations on the use of some sugars, notably fructosides, in reduction, epoxida-tion, and indium-promoted allylations, Plusquellec and coworkers recently reported the use of IM sucrose or ethyl fructofuranoside as additives in the aqueous aldolisation reaction of methyl 4-methylcyclo-hexanone with m-nitrophenylbenzaldehyde (and diversely functionalized analogues) performed in the presence of organocatalysts such as L-pro-line (Scheme 8, Table 6). Significant variations in the anti-syn selectivity were observed. 

In 1991, Li and Chan reported the use of indium to mediate Barbier-Grignard-type reactions in water (Eq. 8.49).108 When the allylation was mediated by indium in water, the reaction went smoothly at room temperature without any promoter, whereas the use of zinc and tin usually requires acid catalysis, heat, or sonication. The mildness of the reaction conditions makes it possible to use the indium method to allylate a methyl ketone in the presence of an acid-sensitive acetal functional group (Eq. 8.50). Furthermore, the coupling of ethyl 2-(bromomethyl)acrylate with carbonyl compounds proceeds equally well under the same reaction conditions, giving ready access to various hydroxyl acids including, for example, sialic acids. 

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