Ketones addition reactions with

The aromatic primary and secondary stibines are readily oxidized by air, but they are considerably more stable than their aHphatic counterparts. Diphenylstibine is a powerful reducing agent, reacting with many acids to Hberate hydrogen (79). It has also been used for the selective reduction of aldehydes and ketones to the corresponding alcohols (80). At low temperatures, diphenylstibine undergoes an addition reaction with ketene (81) ... 

Methylarsine, trifluoromethylarsine, and bis(trifluoromethyl)arsine [371-74-4] C2HAsF, are gases at room temperature all other primary and secondary arsines are liquids or solids. These compounds are extremely sensitive to oxygen, and ia some cases are spontaneously inflammable ia air (45). They readily undergo addition reactions with alkenes (51), alkynes (52), aldehydes (qv) (53), ketones (qv) (54), isocyanates (55), and a2o compounds (56). They also react with diborane (43) and a variety of other Lewis acids. Alkyl haUdes react with primary and secondary arsiaes to yield quaternary arsenic compounds (57). 

Aldehydes and ketones undergo reversible addition reactions with alcohols. The product of addition of one mole of alcohol to an aldehyde or ketone is referred to as a hemiacetal or hemiketal, respectively. Dehydration followed by addition of a second molecule of alcohol gives an acetal or ketal. This second phase of the process can be catalyzed only by acids, since a necessary step is elimination of hydroxide (as water) from the tetrahedral intermediate. There is no low-energy mechanism for base assistance of this... 

Perhaps the most striking difference between conjugated and nonconjugated dienes is that conjugated dienes undergo an addition reaction with alkenes to yield substituted cyclohexene products. For example, 1,3-butadiene and 3-buten-2-one give 3-cycIohexenyl methyl ketone. 

Aldehydes and unhindered ketones undergo a nucleophilic addition reaction with HCN to yield cyanohydrins, RCH(OH)C=N. Studies carried out in the early 1900s by Arthur Eapworth showed that cyanohydrin formation is reversible and base-catalyzed. Reaction occurs slowly when pure HCN is used but rapidly when a small amount of base is added to generate the nucleophilic cyanide ion, CN. Alternatively, a small amount of KCN can be added to HCN to catalyze the reaction. Addition of CN- takes place by a typical nucleophilic addition pathway, yielding a tetrahedral intermediate that is protonated by HCN to give cyanohydrin product plus regenerated CN-. 

We said in Section 19.10 that aldehydes and ketones undergo a rapid and reversible nucleophilic addition reaction with alcohols to form hemiacetals. 

It has long been known that a, / -unsaturated sulfones resemble a, /i-unsaturated ketones and aldehydes in undergoing addition reactions with nucleophilic reagents43. These reactions are initiated by nucleophilic attack at the carbon to the sulfone group ... 

Titanium enolates can be prepared from lithium enolates by reaction withatrialkoxy-titanium(IV)chloride,suchasfra-(isopropoxy)titaniumchloride.21 Titanium enolates are usually prepared directly from ketones by reaction with TiCl4 and a tertiary amine.22 Under these conditions, the Z-enolate is formed and the aldol adducts have syn stereochemistry. The addition step proceeds through a cyclic TS assembled around titanium. 

When the carbonyl carbon is substituted with a potential leaving group, the tetrahedral adduct can break down to regenerate a C=0 bond and a second addition step can occur. Esters, for example are usually converted to tertiary alcohols, rather than ketones, in reactions with Grignard reagents. 

Amides, especially of piperidine and morpholine, give good yields of ketones on reaction with organocerium reagents.203 It has been suggested that the morpholine oxygen may interact with the oxyphilic cerium to stabilize the addition intermediate. 

Ketones and aromatic aldehydes undergo facile addition reactions with CDI (A) or better with A -sulfmyldiimidazole (B) to give diimidazolylmethanes and N-alkylene-imidazoles, depending on the presence of hydrogen atoms a to the carbonyl group ... 

Double-bond compounds between heavier group 14 and 16 elements (heavy ketones) undergo ready addition reactions with various reagents to give the corresponding single-bond compounds. The details of the reactivities are described in the next section (Schemes 20 and 21). 

As with other reactions, silyl esters of phosphorus acids constitute an important and useful category of reagents for conjugate addition reactions. With aldehydes, ketones, and esters, the silyl ester linkage is transferred to the carbonyl oxygen, facilitating the completion of the reaction, generating the free carbonyl or ester upon workup with a protic solvent (Equation 3.25). 

Wipf has shown that this method is quite general and tolerates several functional groups, such as ethers, thioethers, silanes, halides, aromatic rings, and olefins. The iodoalkyne 64 is readily carbometalated and after treatment with the dialkynylcuprate 59 furnishes the functionalized copper reagent 65, which smoothly undergoes 1,4-addition reactions with enones. Thus, in the case of 2-cyclohexenone, the functionalized ketone 66 is produced in 85% yield (Scheme... 

The anions of primary nitramines, like other nucleophiles, can undergo Michael 1,4-addition reactions with a range of a,-unsaturated substrates to form secondary nitramines of varying molecular complexity (Equation 5.18). Kissinger and Schwartz prepared a number of secondary nitramines from the condensation of primary nitramines with a,/3-unsaturated ketones, esters, amides and cyanides. In a standard experiment a solution of the primary nitramine and... 

In the reverse reaction, the addition anion reforms the carbonyi group by expeiiing the enoiate anion as ieaving group. This reverse aldol reaction is sufficientiy important in its own right, and we shaii meet exampies. Note that, as we saw with simpie aidehyde and ketone addition reactions, aidehydes are better eiectrophiies than ketones (see Section 7.1.1). This arises from the extra alkyl group in ketones, which provides a further inductive effect and extra steric hindrance. Accordingly, the aldol reaction is more favourable with aldehydes than with ketones. With ketones, it is absolutely essential to disturb the equilibrium in some way. 

In the aldol reaction, we saw an enolate anion acting as a nucleophile leading to an addition reaction with aldehydes and ketones. 

Asymmetric alkynyl additions to aldehydes by prior, separate generation of the alkynylides (e.g. dialkylzinc reagents) have recently been reviewed and are a topic of current research [10], They will not be covered in the context of this chapter. Instead, in line with the theme of this book, this chapter will focus on the metala-tion of terminal alkynes by activation of the terminal C-H and the use of the corresponding metal acetylides in aldehyde and ketone addition reactions. 

Benzophenone (Amax = 340 nm, log e = 2.5, n-ir electronic transition) can be used as a photochemical reagent and eq. 4.25 shows a radical Michael-addition reaction with benzophenone. The formed benzophenone biradical (triplet state, Tx) abstracts an electron-rich a-hydrogen atom from methyl 3-hydroxypropanoate (62) to generate an electron-rich a-hydroxy carbon-centered radical [III], then its radical adds to the electron-deficient (3-carbon of a, (3-unsaturated cyclic ketone (63) through the radical Michael addition. The electrophilic oxygen-centered radical in the benzophenone biradical abstracts an electron-rich hydrogen atom from methyl 3-hydroxypropanoate (62) [70]. So, an a-hydroxy carbon-centered radical [III] is formed, and an electron-deficient a-methoxycarbonyl carbon-centered radical [III7] is not formed. 

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