Indium promoter

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... 

Two classes of promoter have been identified for iridium catalysed carbonylation (i) transition metal carbonyls or halocarbonyls (ri) simple group 12 and 13 iodides. Increased rates of catalysis are achieved on addition of 1-10 mole equivalents (per Ir) of the promoter. An example from each class was chosen for spectroscopic study. An Inis promoter provides a relatively simple system since the main group metal does not tend to form carbonyl complexes which can interfere with the observation of iridium species by IR. In situ HP IR studies showed that an indium promoter (Inl3 Ir = 2 1) did not greatly affect the iridium speciation, with [MeIr(CO)2l3] being converted into [Ir(CO)2l4] as the batch reaction progressed, as in the absence of promoter. 

With a ruthenium promoter (added as [Ru(CO)4l2]), r(CO) bands due to Ru iodo-carbonyls dominated the spectrum, precluding the easy observation of iridium species. Before injection of the Ir catalyst, absorptions due to [Ru(CO)2l2(sol)2], [Ru(CO)3l2(sol)] and [Ru(CO)3l3] are present. After injection of the iridium catalyst (Ru Ir = 2 1), [Ru(CO)3l3] becomes the dominant Ru species (Figure 3.11(b)). The observations indicate that the Ru(II) promoter has a high affinity for iodide and scavenges Hl(aq) as H30 [Ru(CO)3l3] . An indium promoter is believed to behave in a similar manner to form H30 [Inl4] . These promoter species also catalyse the reaction of Hlj q) with methyl acetate (Eq. (3)), which is an important organic step in the overall process. 

Indium-promoted organometallic reactions are greatly accelerated in water, especially when the coreactant carbonyl compound also has good water solubility. Otherwise, aqueous tetrahydrofuran can be used. To date, indium is the most effective metal for promoting Barbier-type reactions under aqueous conditions. As illustrated here, this is of particular value where formaldehyde is concerned, since the need to generate monomeric formaldehyde by thermal cracking is avoided. 

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 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... 

Indium-promoted addition of (Z)-2-(bromomethyl)-2-butenoate to ct-protected hydroxy aldehydes in water results in the selective formation of diastereomer 37 of the possible four stereoisomers 36-39 via the Felkin-Anh transition state (Scheme 40).170... 

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... 

The indium-promoted intramolecular cyclization of -substituted (Z)- 52 and ( )-7-bromo-5-heptenophenones 53 in aqueous THF gives yjw-2-vinylcyclopentanol 54 irrespective of the double-bond geometry in the starting material. These results suggest that the indium-mediated reactions involve intramolecularly coordinated transition states, where the development of a as 5/6-bicyclic framework is most energetically feasible (Scheme 53).210... 

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... 

Indium-promoted reaction of l,4-dibromo-2-butyne with carbonyl compounds gives 1,3-butadiene derivatives via the allenic indium intermediates (Scheme 56).220 Similar indium-mediated l,3-butadien-2-ylation reactions of optically pure azetidine-2,3-diones have been investigated in aqueous media, offering a convenient asymmetric entry to the 3-substituted 3-hydroxy-/ -lactam moiety (Equation (40)). The diastereoselectivity of the addition reaction is controlled by the bulky chiral auxiliary at Q4 221 222... 

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... 

Cho, D. H., Kim, J. G., Jang, D. O. Indium-promoted convenient method for acylation of alcohols with acid chlorides. Bull. Korean Chem. Soc. 2003, 24,155-156. 

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. 

The indium-promoted reaction of f-cinnamyl bromide with a-alkoxy aldehyde 295 affords the expected 3,A-anti/4,5-nnti diastereomer as the major product (Scheme 10-101). Normal Felkin-type selectivity through transition structure xxviii is restored here in view of the -configuration of the indium reagent. 

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 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. 

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