Of RCHO

On the basis of these experimental results, a possible mechanism has been proposed for the reaction of 1-215 with Sml2 (Scheme 1.52). After formation of the syn-complex A, a rearrangement occurs to give the aldehyde B, which coordinates to the added aldehyde RCHO to afford complex C. Subsequent samarium-catalyzed nucleophilic attack of the secondary alcohol to the carbonyl of RCHO generates a hemiacetal, D. There follows an irreversible intramolecular 1,5-hydride transfer via... 

Alcohols are the most important precursors in the synthesis of carbonyl compounds, being readily available. More complex alcohols are prepared by reaction of Grignard reagents with simpler carbonyl compounds. Ordinarily MnO and Cx OY in acid are used to oxidize 2° RjCHOH to RjCO. However, to oxidize 1° RCHjOH to RCHO without allowing the ready oxidation of RCHO to RCOOH, requires special reagents. These include (a) pyridinium chlorochromate (pcc),... 

Ketones can be prepared by (a) dialkylating 1,3-dithiane before hydrolysis, or (ft) forming the dithiane of RCHO and then monoalkylating. 

Other a-fluorinated carboethoxy substrates have been utilized in Reformatsky reactions. Treatment of ethyl dibromofluoroacetate with aldehydes or ketones in presence of zinc and EtaAlCl gave diastereomeric a -brorno-a-fluoro /i-hydroxyalkanoic esters in good yield (49-77%) (equation 120)177. Use of 2 equivalents each of RCHO, Zn and Et2AlCl gave the double coupled products in good yield. 

Asymmetric allylation of RCHO.1 The reagent converts aldehydes to homoal-lylic alcohols in 94-99% ee, which is significantly higher than the enantioselectivi-ties obtained with B-allyl(diisopinocampheyl)borane. The enantiomer of ( + )-2-car-ene is not known, but B-allylbis(4-isocaranyl)borane (2) behaves as an enantiomer of 1 in allylation of aldehydes. 

Oxygenation of RCHO to RCOOH.1 This oxidation can be effected by oxygen when catalyzed by nickel complexes such as bis(acetylacetonato)nickel, Ni(acac)2. However, the highest conversion and yields are obtained with the complex prepared from l,3-di(p-methoxyphenyl)-l,3-propanedionate, Ni(dmp)2. Ether or an alcohol... 

Reaction of RCHO with 1,3-diene monoepoxides.4 The monoepoxides of butadiene or of isoprene after treatment with CrCl2 and 1A1 (2 l) react with aldehydes to form cis-l,3-diols with a quaternary center at C2. 

RCHO - RCmCH. A new two-step method for conversion of RCHO to RC=CH involves conversion first to a 1,1-dibromoalkene, RCH=CBr2, followed by debromination. The most convenient reagent for this second step is magnesium ia refluxing THF. 

Note that generation of an a,p-epoxysilane from an aldehyde followed by addition of water in the presence of acid constitutes the transformation of RCHO to RCH2CHO. 

Asymmetric allylboration of RCHO. (S)-l reacts with aliphatic or aryl aldehydes or with a,p-enals to form homoallylic alcohols in 92-97% ee and 80-92% chemical yield. The chemical and optical yields are higher than those obtained with B-allyldiisopinocamphenylborane (14,12), with allylboronates modified with tartrates, or with B-allyltrimethylsilylboronates. The high asymmetric induction is believed to result from steric effects rather than electronic effects. 

Crotylization of RCHO.1 (E)- and (Z)-Crotyltrifluorosilanes add to aldehydes in the presence of CsF to give anti- and vyn-p-methylhomoallyl alcohols, respectively, with high diastereoselectivity. 

Reaction of RCHO with CJfCH=CHCH1Cl. This reaction can be regio-selective and f/ireo-selective when mediated by Sn and Al. The reaction of benz-aldehyde with cinnamyl chloride provides the anfi-homoallylic alcohol as the only detectable product. This diastereoselectivity obtains generally with aliphatic or aromatic aldehydes. The reaction with enals under the same conditions provides only the 1,2-adducts, again with anti-selectivity (equation I). The reaction of 2-phenylpropanal with 1 provides a mixture of homoallylic alcohols in the ratio 3 1, with anti-selectivity at the C—C bond formed in the reaction (equation II). 

Aldehyde oxidases (19) occur in the liver of mammals and catalyze the oxidation of RCHO RCCTH for R = Me, this reaction represents the second step in the conversion of ethanol to acetic acid the first step is catalyzed by the Zn enzyme, alcohol dehydrogenase. 

Ruthenium(II) Treatment of [Ru(NH3)5(OH2)]2+ or [Ru(NH3)5(acetone)]2+ with L or [RuCl(NH3)5]2+ with zinc amalgam in the presence of L yields [RuL(NH3)5]2+ (L = acetonitrile, benzonitrile,358 substituted benzonitrile,196 358 359 acrylonitrile,360 hydrogen cyanide,36,37 ethyl cyano-formate,361 dicyanamide, malononitrile, substituted malononitrile, tricyanomethanide,362 4-cyano-l-methylpyridinium196). Reaction of a hundred-fold excess of RCHO (R = Ph, Me) with [Ru(NH3)6]2+ under alkaline conditions yields [Ru(NH3)sNCR]2+.363-365 The likely mechanism of this reaction is given in Scheme 12. An alternative route to nitrile complexes is by reaction of [Ru(NH3)sOH2]2+ with aldoximes, e.g. RMeC=NOH, to afford [Ru(NH3 )5 (NCMe)]2 + and... 

Aldehydes and ketones exhibit dipole-dipole interactions because of their polar carbonyl group. Because they have no O-H bond, two molecules of RCHO or RCOR are incapable of intermolecular hydrogen bonding, making them less polar than alcohols and carboxylic acids. How these intermolecular forces affect the physical properties of aldehydes and ketones is summarized in Table 21.1. 

In contrast to the observations of McNesby and Davis,the oxygen pressure and the aldehyde concentration have symmetrical kinetic effects the curves representing the variations in the rate as a function of Po, and as a function of [RCHO], respectively, are of similar shape (Figs. 1 and 2). 

In the general case, the observed course of the variations of F as a function of Pq, or as a function of [RCHO] is similar to that envisaged on the basis of the theoretical relationship (6). The experimental results are compatible (Figs. 1 and 2) with the following values (at 3°C.) ... 

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