Esters conjugation with carbonyl group

Most stable enol double bond conjugated with carbonyl group ester carbonyl stabilized by resonance... 

This compound is an ester, and the carbonyl group is conjugated with the aromatic ring. The predicted position is 1740 — (20 to 40) = 1720 to 1700 cm-1. 

We ve already discussed this sequence of reactivity in relation to acid derivatives in Chapters 12 and 14— make sure you understand the reason forthe ordering of ester > amide > carboxylate. Here we re adding on aldehyde (the most reactive, for steric reasons—it is the least hindered) and ketone (more reactive than esters because the carbonyl group is not stabilized by conjugation with a lone pair). 

Alcohol (34) is needed and we shall want to use a photocycloaddition to make some derivative of it (ether or ester). One partner in the cycloadd ition will be nucleophilic (CH2=CH0R) so we need a carbonyl group conjugated with the cyclohexene. FGA is required. 

The previous sections dealt with reactions in which the new carbon-carbon bond is formed by addition of the nucleophile to a carbonyl group. Another important method for alkylation of carbon nucleophiles involves addition to an electrophilic multiple bond. The electrophilic reaction partner is typically an a,(3-unsaturated ketone, aldehyde, or ester, but other electron-withdrawing substituents such as nitro, cyano, or sulfonyl also activate carbon-carbon double and triple bonds to nucleophilic attack. The reaction is called conjugate addition or the Michael reaction. 

Diastereoselectivity in the aldol and the conjugate additions of 2 -hydroxy-1,T-binaphthyl ester enolates with a variety of carbonyl electrophiles has also been explored the tendency of the ester enolates, generated by BuLi, to react with aldehydes to give threo products preferentially with high diastereoselectivity has been interpreted in terms of an acyclic transition state of chelated lithium enolate involving the aldehyde carbonyl and the 2 -hydroxy group. 

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