Cyclohexanone forming enolate anion

These mechanistic interpretations can also be applied to the hydrogenation of cyclohexanones. In acid, the carbonium ion (19) is formed and adsorbed on the catalyst from the least hindered side. Hydride ion transfer from the catalyst gives the axial alcohol (20). " In base, the enolate anion (21) is also adsorbed from the least hindered side. Hydride ion transfer from the catalyst followed by protonation from the solution gives the equatorial alcohol (22). 

What reaction would occur if one attempted to use butyllithium to form the enolate anion of cyclohexanone ... 

The reaction pathway of the present photochemical reaction is not clear but presumably proceeds as shown in Scheme 31. The radical ion pair of 73 and DCN is formed on photoirradiation. Electron transfer then occurs between the radical anion of EXTN and cyclohexanone, forming radical ion pair of CR73 and AR14b. The radical cation CR73 cleaves into methoxystannane and aryloxymethyl radical R73, which couples with AR14b to give the enolate (or enol) of 74. 

Their stability at low temperature means that lithium enolates are usually preferred, but sodium and potassium enolates can also be formed by abstraction of a proton by strong bases. The increased separation of the metal cation from the enolate anion with the larger alkali metals leads to more reactive but less stable enolates. Typical very strong Na and K bases include the hydrides (NaH, KH) or amide anions derived from ammonia (NaNH2, KNH2) or hexamethyldisilazane (NaHMDS, KHMDS). The instability of the enolates means that they are usually made and reacted in a single step, so the base and electrophile need to be compatible. Here are two examples of cyclohexanone alkylation the high reactivity of the potassium enolate is demonstrated by the efficient tetramethylation with excess potassium hydride and methyl iodide. 

Just as an ester enolate anion reacts with an aldehyde or ketone via acyl addition, it is also reasonable that the enolate anion of an aldehyde or a ketone may react with an ester via acyl substitution. In the former reaction, the ester enolate is the nucleophile in the latter reaction, a ketone or aldehyde enolate is the nucleophile. When cyclohexanone (80) is treated with LDA (THF, -78°C) and then with methyl propanoate, the initial product is 81. Loss of OMe completes the acyl substitution sequence to give diketone 82. There is nothing special or unusual about these two variations. Virtually any ketone or aldehyde enolate reacts with an ester to form 1,3-diketones such as 82. 

A classical reaction of an enolate anion with a conjugated carbonyl leads to a bicyclic derivative. When cyclohexanone (58) is heated with methyl vinyl ketone (10) in the presence of ethanoUc KOH, the final product (after hydrolysis) is bicyclic ketone 64. This process is called the Robinson annulation, after Sir Robert Robinson (England 1886-1975). It begins with the reaction of 58 with KOH to form the enolate anion (59). Under these conditions, Michael addition to 10 is faster than self-condensation of the ketone (see Chapter 22, Section 22.2), and the product is enolate anion 60. 

The anion Z has a finite lifetime and propagates further by stepwise addition of more monomer. However, death of the polymer enolate ion can occur by a spontaneous, thermally-induced cyclization to form a terminal,-substituted cyclohexanone ring (2) which results in termination. ... 

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