Additions to Aldehydes and Ketones

Chemoselective 1,2-Addition of Oi anomanganese Reagents to Carbonyl Compounds 

On the other hand, aliphatic (n-, s- or t-alkyl), ethylenic and aromatic aldehydes have been selectively converted in high yields into the corresponding secondary alcohols in the presence of aliphatic, ethylenic or aromatic ketones. 

The following example is interesting since propylmanganese bromide selectively adds to the conjugated carbonyl group that is the more accessible but also the less reactive (electronic effect). This result underlines the importance of the 

In general, addition to aldehydes and ketones is understood to mean that either the oxygen of the carbonyl group is replaced by some other functionality (usually 

the attentive reader will not have failed to note that both Section A (Oxidation of Aldehydes and Ketones) and Section B (Reduction of Aldehydes and Ketones) in this chapter involve addition to the carbonyl group (C=0). Thus, as shown in Section A, processes that result in oxidation of the carbonyl group (C=0) proceed from initial attack at the sp -hybridized carbon of the carbonyl (C=0) by an electron rich species. The xp -hybridized intermediate resulting from that attack is ultimately consumed when the carbon-hydrogen aldehydic (0=C-H) or the carbon-carbon (0=C-C) ketonic bond breaks. Similarly, in reduction (Section B), the processes involving hydride ion transfer are shown as attack of hydride (H ) donating species onto the xp -hybridized carbon of the carbonyl (C=0) with rehybridization at carbon to sp and eventual protonation at oxygen. 

AdditioD ReactioDS to Aldehydes and Ketones Reactions at the Carbonyl Carbon (C-0) 

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The next section explores the mechanism of nucleophilic addition to aldehydes and ketones There we 11 discuss their hydration a reaction m which water adds to the C=0 group After we use this reaction to develop some general principles we 11 then survey a number of related reactions of synthetic mechanistic or biological interest... 

This pattern of increased reactivity resulting from carbonyl group prolonalion has been seen before m nucleophilic additions to aldehydes and ketones (Section 17 6) and... 

Although the present chapter includes the usual collection of topics designed to acquaint us with a particular class of compounds, its central theme is a fundfflnental reaction type, nucleophilic addition to carbonyl groups. The principles of nucleophilic addition to aldehydes and ketones developed here will be seen to have broad applicability in later chapters when transfonnations of various derivatives of carboxylic acids are discussed. 

Since the first reported directed aldol condensation using lithiated imines1. few methods concerning the diastereo- and enantioselectivity of their addition to aldehydes and ketones have been published. 

Phenyl trimethylsilylethyne (Chapter 20) undergoes a fluoride-ion-catalysed addition to aldehydes and ketones. This provides a remarkably mild, relatively non-basic method for the generation of an alkynyl anion or its equivalent. 

Scheme 7.4 illustrates some of the important synthetic reactions in which organolithium reagents act as nucleophiles. The range of reactions includes S/v2-(ype alkylation (Entries 1 to 3), epoxide ring opening (Entry 4), and formation of alcohols by additions to aldehydes and ketones (Entries 5 to 10). Note that in Entry 2, alkylation takes place mainly at the 7-carbon of the allylic system. The ratio favoring 7-alkylation... 

Another synthetically useful reaction involves the addition to aldehydes and ketones of carbanions, e.g. (100), derived from aliphatic nitro... 

The stereoselectivity of addition to aldehydes and ketones has been of considerable interest.111 112 With benzaldehyde, the addition of 2-butenylstannanes catalyzed by BF3 gives the syn isomer, irrespective of the stereochemistry of the butenyl group.113... 

Addition reactions occur in compounds having n electrons in carbon-carbon double (alkenes) or triple bonds (alkynes) or carbon-oxygen double bonds (aldehydes and ketones). Addition reactions are of two types electrophilic addition to alkenes and alkynes, and nucleophilic addition to aldehydes and ketones. In an addition reaction, the product contains all of the elements of the two reacting species. 

Bromo-l-lithiocyclopropanes, readily obtained by transmetalation of 1,1-dibromocyclo-propanes with butyllithium in tetrahydrofuran at — 100 CC, undergo addition to aldehydes and ketones forming bromohydrins. On warming, before workup, the adducts from ketones (but not from aldehydes) eliminate lithium bromide and cyclizc to oxaspiropentanes, which may be rearranged to cyclobutanones by treatment with acids (Table 6).76-78... 

Aniline is a primary amine and undergoes nucleophilic addition to aldehydes and ketones to form imines. 

Lithium aluminum hydride is a very strong reducing agent that will reduce many functional groups in addition to aldehydes and ketones. Sodium borohydride is a much weaker reducing agent that basically will reduce only aldehydes and ketones to alcohols. 

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