Aldehydes by carbonylation

Carreira and Kruger reported facile transmetallation of silicon enolates to other soft metal enolates including Gu derivatives.499 They reasoned that the use of soft metal fluoride complexes enabled silyl metal transmetallation with catalytic use of a soft metal source. The concept is illustrated in Scheme 103. Normal Lewis acid-catalyzed reactions of silicon enolates with aldehydes proceed via activation of aldehydes by carbonyl oxygen coordination to Lewis acids, as shown in the upper equation of Scheme 103. A key step for catalytic turnover is the desilyation of 233 by the... 

The synthetic utility of the carbonylation of zirconacycles was further enhanced by the development of a pair of selective procedures producing either ketones or alcohols [30] and has been extensively applied to the synthesis of cyclic ketones and alcohols, most extensively by Negishi [22—27,29—33,65,87,131—134], as detailed below in Section I.4.3.3.4. The preparation of unsaturated aldehydes by carbonylation with CO is not very satisfactory. The use of isonitriles in place of CO, however, has provided a useful alternative [135], and this has been applied to the synthesis of curacin A [125]. Another interesting variation is the cyanation of alkenes [136]. Further developments and a critical comparison with carbonylation using CO will be necessary before the isonitrile reaction can become widely useful. The relevant results are shown in Scheme 1.35. 

Synthesis of aldehydes by carbonylation. Brown s original synthesis of aldehydes by reaction of trialkylboranes with carbon monoxide in the presence of lithium trimethoxyaluminum hydride (see Carbon monoxide, 2, 60) sufFered from the disadvantage that only one of the three alkyl groups was utilized thus the maxi-... 

Bis(9-borabicyclo [3.3.1]nonane) is a useful reagent for synthesis of aldehydes by carbonylation of olefins.17... 

Trifluoroacetic acid hydrogen chloride Aldehydes by carbonylation H... 

Fructose, a /3-hydroxy ketone, is then cleaved into two three-carbon molecules—one ketone and one aldehyde—by a reverse aldol reaction. Still further carbonyl-group reactions then occur until pyruvate results. 

A solid-phase version of the palladium-catalyzed carbonyl allylation of aldehydes by allylic alcohol has been described. Thus, allylation of resin-bound aldehyde (P = Merrifield resin) with allylic alcohols (e.g., MeCH=CHCH2OH) in the presence of SnCl2 afforded the homoal-lylic alcohols under different solvent conditions, in DMSO and aqueous DMSO respectively (Eq. 8.45).102... 

Gordon used a household microwave oven for the transfer hydrogenation of benz-aldehyde with (carbonyl)-chlorohydridotris-(triphenylphosphine)ruthenium(II) as catalyst and formic acid as hydrogen donor (Eq. 11.43) [61]. An improvement in the average catalytic activity from 280 to 6700 turnovers h-1 was achieved when the traditional reflux conditions were replaced by microwave heating. 

Fluoride ion is effective in promoting the reduction of aldehydes by organosil-icon hydrides (Eq. 161). The source of fluoride ion is important to the efficiency of reduction. Triethylsilane reduces benzaldehyde to triethylbenzyloxysilane in 36% yield within 10-12 hours in anhydrous acetonitrile solvent at room temperature when tetraethylammonium fluoride (TEAF) is used as the fluoride ion source and in 96% yield when cesium fluoride is used.83 The carbonyl functions of both p-anisaldehyde and cinnamaldehyde are reduced under similar conditions. Potassium bromide or chloride, or tetramethylammonium bromide or chloride are not effective at promoting similar behavior under these reaction conditions.83 Moderate yields of alcohols are obtained by the KF-catalyzed PMHS, (EtO SiH, or Me(EtO)2SiH reduction of aldehydes.80,83,79... 

Scheme 1.34. Formation of acyl-zirconocene derivatives by carbonylation and their conversion into aldehydes, carboxylic acids, and derivatives thereof.

As shown in Scheme 4.16, the retrosynthetic process proceeds as follows i) FGI (substitution of the unconjugated aldehyde by an acetal group and the conjugated double bond by an OH group) ii) retro-aldol disconnection of the 1,3-C system iii) "reconnection" of the resulting 1,6-D system to a 6-membered ring iv) FGI (substitution of the double bond by an OH group and the acetal by a carbonyl... 

Varieties of primary and secondary alcohols are selectively oxidized to aldehyde or carbonyl compounds in moderate to excellent yields as summarized in Table 3. As can be seen, /(-substituted benzyl alcohols (e.g., -Cl, -CH3, -OCH3, and -NO2) yielded > 90% of product conversion in 3-4 h of reaction time with TOP in the range of 84-155 h (entries 2-5, Table 3), Heterocyclic alcohols with sulfur- and nitrogen-containing compoimds are found to show the best catalytic yield with TOP of 1517 and 902 h for (pyrindin-2-yl)methanol and (thiophene-2-yl) methanol, respectively (entries 9 and 10, Table 3). Some of aliphatic primary alcohols (long chain alcohols) and secondary alcohols (cyclohexanol, its methyl substituted derivatives and norboman-2-ol) are also selectively oxidized by the membrane catalyst (entries 11-14 and 15-17, Table 3) with TOP values in the window of 8-... 

Significantly higher levels of enantioselectivity can be obtained with aromatic and unsaturated aldehydes by making use of the corresponding metal carbonyl complexes (Eq. The selectivity is higher in toluene as solvent, and the... 

When ozonolysis is done in alcoholic solvents, the carbonyl oxide fragmentation product can be trapped as an a-hydroperoxy ether.146 Recombination to the ozonide is then prevented, and the carbonyl compound formed in the fragmentation step can also be isolated. If the reaction mixture is treated with dimethyl sulfide, the hydroperoxide is reduced and the second carbonyl compound is also formed in good yield.147 This procedure prevents oxidation of the aldehyde by the peroxidic compounds present at the conclusion of ozonolysis. 

The ozonolyses of enol ethers has been reviewed <91MI 4l6-0l>. The relative dipolarophilicity of certain species to attack by carbonyl oxides has been investigated and, in general, the order of reactivity is aldehydes > enol ethers > esters ss ketones. It is apparent that enol ethers are very reactive towards carbonyl oxides, so much so that 1,2-dioxolane formation can be a major reaction pathway (especially for formaldehyde-O-oxide) <85JOC3365>. 

---