Carbonyl compound double

When the sodium cyanoborohydride reduction of tosylhydrazones discussed on page 150 is applied to a, 8-unsaturated carbonyl compounds, double-bond migration invariably occurs. Suggest a mechanism for this process. 

Figure 8.21 1,4-Addition to carbonyl compound double bond.

So we can disconnect any a,p-imsaturated carbonyl compound along the double bond, writing CH2 at one end and C=0 at tbe other. 

One extra disconnection is all we need to cope with misaturated heterocycles. If a nitrogen atom is joined to a double bond in a ring, we have a cyclic enamine. This is made from an amine and a carbonyl compound in the same way as ordinary enamines ... 

The addition of acetylides to oxiranes yields 3-alkyn-l-ols (F. Sondheimer, 1950 M.A. Adams, 1979 R.M. Carlson, 1974, 1975 K. Mori, 1976). The acetylene dianion and two a -synthons can also be used. 1,4-Diols with a carbon triple bond in between are formed from two carbonyl compounds (V. Jager, 1977, see p. 52). The triple bond can be either converted to a CIS- or frans-configurated double bond (M.A. Adams, 1979) or be hydrated to give a ketone (see pp. 52, 57, 131). 

Another widely used route to cyclopropanes involves the addition of sulfoniutn ylides to a,/3-unsaturated carbonyl compounds (S.R. Landor, 1967 R. Sowada, 1971 C.R. Johnson, I973B, 1979 B.M. Trost, 1975 A). Non-activated double bonds are not attacked. Sterical hindrance is of little importance in these reactions because the C—S bond is extraordinarily long... 

Primary and secondary amines also react with epoxides (or in situ produced episulfides )r aziridines)to /J-hydroxyamines (or /J-mercaptoamines or 1,2-diamines). The Michael type iddition of amines to activated C—C double bonds is also a useful synthetic reaction. Rnally unines react readily with. carbonyl compounds to form imines and enamines and with carbo-tylic acid chlorides or esters to give amides which can be reduced to amines with LiAlH (p. Ilf.). All these reactions are often applied in synthesis to produce polycyclic alkaloids with itrogen bridgeheads (J.W. Huffman, 1967) G. Stork, 1963 S.S. Klioze, 1975). 

Addition of dihydrosilane to a, /J-unsaturated carbonyl compounds such as citral (49), followed by hydrolysis, affords saturated citroneJlal (50) directly. The reaction is used for the selective reduction of conjugated double bonds[45,46]. In addition to Pd catalyst, the use of a catalytic amount of... 

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. 

Alkenes are cleaved to carbonyl compounds by ozonolysis This reaction IS useful both for synthesis (preparation of aldehydes ketones or car boxyhc acids) and analysis When applied to analysis the carbonyl com pounds are isolated and identified allowing the substituents attached to the double bond to be deduced... 

To identify the carbonyl compound and the ylide required to produce a given alkene mentally disconnect the double bond so that one of its carbons is derived from a car bonyl group and the other is derived from an ylide Taking styrene as a representative example we see that two such disconnections are possible either benzaldehyde or formaldehyde is an appropriate precursor... 

The carbonyl group withdraws rr electron density from the double bond and both the carbonyl carbon and the p carbon are positively polarized Their greater degree of charge separation makes the dipole moments of a p unsaturated carbonyl compounds signifi cantly larger than those of comparable aldehydes and ketones... 

The diminished rr electron density m the double bond makes a p unsaturated aide hydes and ketones less reactive than alkenes toward electrophilic addition Electrophilic reagents—bromine and peroxy acids for example—react more slowly with the carbon-carbon double bond of a p unsaturated carbonyl compounds than with simple alkenes... 

Ordinarily nucleophilic addition to the carbon-carbon double bond of an alkene is very rare It occurs with a p unsaturated carbonyl compounds because the carbanion that results IS an enolate which is more stable than a simple alkyl anion... 

Multiple bonds are revealed clearly by anisotropic effects. Textbook examples include alkynes, shielded along the C=C triple bond, and alkenes and carbonyl compounds, where the nuclei are deshielded in the plane of the C=C and C=0 double bonds, respectively One criterion for distinguishing methyl groups attached to the double bond of pulegone (31), for example, is the carbonyl anisotropic effect. 

Secondary amines cannot form imines, and dehydration proceeds to give carbon-carbon double bonds bearing amino substituents (enamines). Enamines were mentioned in Chapter 7 as examples of nucleophilic carbon species, and their synthetic utility is discussed in Chapter 1 of Part B. The equilibrium for the reaction between secondary amines and carbonyl compounds ordinarily lies far to the left in aqueous solution, but the reaction can be driven forward by dehydration methods. 

Conjugate addition (Sections 10.10 and 18.12) Addition reaction in which the reagent adds to the termini of the conjugated system with migration of the double bond synonymous with 1,4 addition. The most common examples include conjugate addition to 1,3-dienes and to a,(3-unsaturated carbonyl compounds. 

Since Stork et al. introduced as a new synthetic method the alkylation and acylation of carbonyl compounds via enamines, this class of compounds has been the subjeet of intensive studies 1-3). The exceptional physical and chemical behavior of the enamine structure can be ascribed to resonance by conjugation of the unshared pair of electrons of the nitrogen atom with the 77 electrons of the double bond ... 

The formation of enamines from carbonyl compounds and secondary amines usually entails as only questionable structural feature, the possible isomeric position of double bonds in the product. Molecular rearrangements have not presented synthetic limitations. A notable exception is the generation of o-aminophenols on distillation of enamines derived from 2-acylfurans 620,621). 

Examine the geometry of formamide. Is the CN bond shorter than expected for a normal single bond (in methylamine), and closer to that expected for a full double bond (in methyleneimine) Is the CO bond longer than that expected in a carbonyl compound (in formaldehyde), perhaps closer to that appropriate for a single bond (in methanol) Also, compare the electrostatic potential map for formamide with those of formaldehyde and methylamine. Is the CO bond in formamide more or less polar than that in formaldehyde Is the CN bond in formamide more or less polar than that in methylamine Draw whatever Lewis structures are needed to properly describe the geometry and charge distribution of formamide. 

Active carbonyl compounds such as benzaldehyde attack the electron-rich double bond in DTDAFs to give a dipolar adduct, which immediately undergoes dissociation with formation of two molecules of 146 (64BSF2857 67LA155).Tlie existence of by-products such as benzoin led to the synthetic application of thiazolium salts in the acyloin condensation. For example, replacement of the classic cyanide ion by 3-benzyl-4-methyl-5(/3-hydroxyethyl) thiazolium salts allowed the benzoin-type condensation to take place in nonaqueous solvents (76AGE639) (Scheme 57). 

The UV and IR spectra eliminate structures with a CN double bond. The isomerism of nitrones and oxaziranes thus cannot be a result of CIS or traris arrangement of substituents about a double bond. The carbon atoms of an oxazirane are still at the oxidation level of the carbonyl compound used in its syntheses. By acid hydrolysis, for example, 2-terf-butyl-3-phenyloxazirane (9) can be split into benzaldehyde and tert-butylhydroxylamine fEq. (8)]. ... 

The overall process is the addition of a CH-acidic compound to the carbon-carbon double bond of an o ,/3-unsaturated carbonyl compound. The Michael reaction is of particular importance in organic synthesis for the construction of the carbon skeleton. The above CH-acidic compounds usually do not add to ordinary carbon-carbon double bonds. Another and even more versatile method for carbon-carbon bond formation that employs enolates as reactive species is the aldol reaction. 

When the substrate does not contain a reactive carbon-carbon double bond, the ozonolysis procedure appears to provide a convenient and efficient method for the conversion of primary and secondary nitro compounds into carbonyl compounds fEq. 6.7. ... 

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