Aldehydes mediated

The direct addition of simple alkyl groups onto aldehydes is the most challenging in water. Mitzel reported the indium-mediated alkylation of carbonyl compounds with a-sulfur stabilized systems.224 Recently, Li and co-workers reported an efficient addition of simple alkyl halides to aldehydes mediated by Zn/Cul with a catalytic amount of InCl in water (Eq. 8.89).225... 

The aldol reaction between enolsilanes and aldehydes mediated by chiral Lewis acids may be considered the most notable achievement in the area of asymmetric aldol reactions. However, the design of new catalyst systems to tolerate... 

Table 9.58 Enantioselective in situ addition of allenylindium bromide to aldehydes mediated by (-)-cinhonidine.

GRIGNARD-TYPE COUPLING REACTIONS BETWEEN ALKENYL HALIDES (OR TRIFLATES) AND ALDEHYDES, MEDIATED BY THE CrCI2-NiCI2 SYSTEM3... 

Alcohols have been converted into aldehydes mediated by a lipophilic / -cyclodextrin bearing a ferrocene moiety [139]. Efficient indirect in situ electroregeneration of NAD+ and NADP+ for enzymatic oxidations of butanol and 2-hexen-l-ol leading to the corresponding aldehydes using Fe bipyridine and phenanthroline complexes as redox... 

SEGPHOS [271, 272]. Using this complex as a precatalyst, transfer hydrogenation of 1,1-dimethylallene in the presence of diverse aldehydes mediated by isopropanol delivers products of ferf-prenylation in good to excellent yield and with excellent levels of enantioselectivity. In the absence of isopropanol, enantio-selective carbonyl reverse prenylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts. Notably, enantioselective ferf-prenylation is achieved under mild conditions (30-50°C) in the absence of stoichiometric metallic reagents. Indeed, for reactions conducted from the alcohol oxidation level, stoichiometric byproducts are completely absent (Scheme 13). 

New catalytic allylation methodologies continue to emerge. For example, iridium-catalyzed transfer hydrogenation of a-(trimethylsilyl)allyl acetate in the presence of aldehydes mediated by isopropanol and employing the iridium catalyst... 

The 1,3-dipolar cycloaddition of azomethine yUdes with olefins gives rise to pyrrolidines which represent structural elements of organocatalysts, natural products, and drug candidates. Asymmetric metal-catalyzed variants attracted considerable attention over the last few years [64], Recently, Vicario et al. reported an organo-catalytic [3 -i- 2] cycloaddition of azomethine ylides and a,p-unsaturated aldehydes mediated by a chiral secondary amine [65]. 

Donnelly S, Thomas EJ, Fielding M (2004) 1,5-Stereocontrol in reactions of 5-benzyloxy-4-methylpent-2-enyl bromides with aldehydes mediated by Bi(0) synthesis of aliphatic compounds with 1,5-syn-related methyl groups. Tetrahedron Lett 45 6779-6782... 

Recently, Zhu and coworkers have investigated the reaction of the zinc reagent from ethyl 3-bromodifluoromethyl-3-benzyloxyacrylate. The exclusive zinc reagent formed in DMF was the -carbon metallated product (equation 88)82. These workers utilized this reaction to prepare -dilluorovinyl substituted / -hydroxyesters in high yields and high regioselectivity via the reactions of aldehydes mediated by zinc (equation 89)82. 

BINOL-derived phosphoramidites are versatile ligands in palladium-catalysed umpol-ung allylation of aryl aldehydes mediated by diethylzinc.172 The possible roles of allyl-zinc and -palladium species in the mechanism are discussed in detail. 

C-Sucrose. A key step in a synthesis of this saccharide involves as the first step the coupling of a vinyl iodide with an aldehyde mediated by CrCl2 and a trace of NiCl2 (14, 97-98). Thus coupling of the vinyl iodide 1 with the aldehyde 2, derived from D-arabinose, provides an allylic alcohol, which on Mitsunobu inversion provides the threo alcohol 3 as the major product. This is converted to C-sucrose... 

The straightforward addition of 1-alkynes to aldehydes mediated by Gal3 and an amine gives propargylic alcohols in moderate to high yields (Scheme 127).414... 

The reaction of 3-(2-benzyloxyacetyl)thiazolidine-2-thione (2) with an aliphatic aldehyde mediated by tin(II) triflate affords the syn- and an -aldols (3) in the ratio 3 1. This ratio is reversed in the presence of 1.2 equiv. of TMEDA. Addition of the chiral diamine... 

A.2.3 Anthocyanin-Flavanol and Anthocyanin-Anthocyanin Aldehyde-Mediated... 

Cozzi, P. G. Tagliavini, E. Umani-Ronchi, A. Enantioselective Addition of Allylic Silanes and Stannanes to Aldehydes Mediated by Chiral Lewis Acids, Gazz. Chim. Ital. 1997,127, 247-254. 

Table 28 Enantioselecdve Additions of Aryl Grignards with Aldehydes Mediated by (106) or (107) R Ar...

The aldol-type reaction of a-bromo ketones with aldehydes, mediated by CrCh, has been studied by Dubois and coworkers. The reaction is carried out by addition of (241 equation 80) to a solution of (242) and CrCh in THF. The reaction proceeds with high levels of syn selectivity with bulky bromo ketones (241), independent of the substrate aldehyde used (Table 11, entries 1-6). However, the reaction is stereorandom with bromoacetophenone (entry 7) and selectively anti with 2-bromocyclohexanone (entry 8). No explanation of the stereoselectivity has been advanced, but the reaction is believed not to proceed via a simple chromium enolate since no condensation reaction is obtained by addition of (242) to a solution of (241) and CrCh. Moreover, Nozaki and coworkershave demonstrated that chro-mium(II) chloride treatment of 1-bromocyclododecanone followed by treatment with either methyl iodide or TMS-Cl produces only cyclododecanone. 

Another promising asymmetric allylation of aldehydes, mediated by a D-glucose-derived titanium reagent (54), has recently been described... 

Inaba, S., Rieke, R. D. Reformatskii type additions of haloacetonitriles to aldehydes mediated by metallic nickel. Tetrahedron Lett. 1985, 26, 155-156. 

The addition of chiral allylic bromides of the general type 247 to achiral aldehydes mediated by CrCb proceeds with a high degree of stereocontrol in which the bromide acts as the stereodominant component (Scheme 10-81) [148]. In all cases examined, major diastereomer 248 has an all-.vyn arrangement of the y-vinyl and <5-methyl substituents. On the basis of this stereochemical outcome the following conclusions can be drawn (1) the <5-center determines the stereochemical outcome of the newly created stereocenters (y and //), (2) the relative dia-stereoselection of the reaction is not affected by the presence of stereogenic centers in the allylic bromide, and (3) additional stereocenters in the e- and c-posi-tions of the bromide increase the diastereofacial selectivity but have no influence on the sense of the asymmetric induction. 

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