Caibonyl Compounds

The addition of hydrogen cyanide is catalyzed by cyanide ion, but HCN is too weak an acid to provide enough C=N for the reaction to proceed at a reasonable rate. Cyanohydrins aie therefore nonnally prepared by adding an acid to a solution containing the caibonyl compound and sodium or potassium cyanide. This procedure ensures that free cyanide ion is always present in amounts sufficient to increase the rate of the reaction. 

Substitution of deuterium for hydrogen at the a-caibon atom of an aldehyde or a ketone is a convenient way to introduce an isotopic label into a molecule and is readily canied out by treating the caibonyl compound with deuterium oxide (D2O) and base. 

The point was made eaiTier (Section 5.9) that alcohols require acid catalysis in order to undergo dehydration to alkenes. Thus, it may seem strange that aldol addition products can be dehydrated in base. This is another exanple of the way in which the enhanced acidity of protons at the a-caibon atom affects the reactions of caibonyl compounds. Elimination may take place in a concerted E2 fashion or it may be stepwise and proceed through an enolate ion. 

The caibon-caibon bond-fonning potential of the aldol condensation has been extended beyond the self-condensations described in this section to cases in which two different caibonyl compounds react in what aie called mixed aldol condensations. 

In resonance tenns, electron delocalization in a,p-unsaturated caibonyl compounds is represented by contributions from three principal resonance structures ... 

A useful synthesis of polysubstituted pyridines (i.e., 11) is based on the legioselective addition of Uthiated -enaminophosphonates to unsaturated carbonyl compounds. These pyridines can also be obtained via a one-pot reaction from metalated phosphonates and sequential addition of nitriles and unsaturated caibonyl compounds <96TL(37)4577>. 

Caibonyl compounds, simple, enolisation and related reactions of, 18, 1... 

Review H. M. Colquhoun, D. J. Thompson, M. V. Twigg, Cartonylation-Dlrect Synthesis of Caibonyl Compounds, Plenum, New York (1991)... 

Conversion of Phosphorus- or Sulfur-Stabilized C Nucleophiles with Caibonyl Compounds... 

Oximes are cleaved by oxidation, reduction, or hydrolysis in the presence of another caibonyl compound. Some synthetically useful methods are shown below. 

Vin silanes follow a similar course on oxidation with peroxy acid or with ozone. - Depending upon the conditions of oxidation they can be converted either to a carbonyl compound (2) or to the a-hydroxy-caibonyl compound (3), as in Scheme Vinyl silanes are useful synthetic intermediates, and this oxidation rearrangement procedure is an important component in their spectrum of reactivity. 

Table 4 The Oxidative Cleavage of Double Bonds to Caibonyl Compounds by Permanganate...

Table 6 Reaction of (71) with oc,P-Unsaturated Caibonyl Compounds Catalyzed by Phosphine-[Pd(DBA)2] ...

Hydrazinothiazoles, synthesis of, from thiosemicarbazides and a-halo-caibonyl compounds, 251, 256... 

Table 10 Addition of Various AUyltitanium(III) Complexes (RTiCpj) to Caibonyl Compounds...

Uncatalyzed Additions of Nucleophilic Alkenes to C=X Table 4 Condensations of (31) with Caibonyl Compounds Giving Epoxy Sulfoximines ... 

The results obtained in the partial oxidation of various alcohols are given in the Table. 1. It is seen that these oxides are highly selective to the formation of respective caibonyl compounds. 

Camphor oxa/olinc clni.il aiisili.nv 158 Caihanion intermediate in Giignaid reactions 235 Carbenoid intermediates 48 Caibocaiioiis 50 ( aibninaenesialioti 90 Carbon. nucleophilic displacement ai 27 -(>4 Caibonyl compound o 7. /n. 5... 

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