Ethyl acrylate nucleophilic attack

The reaction starts with the (relatively nucleophilic) DABCO undergoing conjugate addition to ethyl acrylate. This will form an enolate that can then attack the acetaldehyde in an aldol reaction. 

Moving to a,/3-unsaturated esters, hydroxide ion and alkoxide ion (hard nucleophiles) react with ethyl acrylate 4.77 by direct attack at the carbonyl group to give ester hydrolysis and exchange, respectively, whereas the /3-dicar-bonyl enolate ion 4.78 (a soft nucleophile) undergoes a Michael reaction. There is no certainty in this latter reaction that the attack of the enolate anion on the carbonyl group is not a more rapid (and reversible) process. 

Hydroxide and alkoxide ions, both hard nucleophiles, react with ethyl acrylate 93, an a,p-unsaturated ester, by direct attack at the carbonyl carbon to bring about ester hydrolysis and ester exchange, respectively. However, the enolate 94, a soft nucleophile, reacts in conjugate manner to form 95 predominantly. In an alternate pathway, it is also likely that the enolate 94 reacts through the oxy anion (hard nucleophile) directiy at the carbonyl carbon (hard electrophile) to generate the species 96, which rearranges in an oxy anion accelerated [3.3] sigmatropic shift manner, as shown, to form 97 and, thus, the above product 95. However, it is not certain that such a direct attack by the enolate is not more rapid and reversible. 

In the late nineteenth century, Michael found that the enolate anion (46) derived from diethyl malonate reacts with ethyl acrylate at the P-carbon (as shown in the illustration) to give an enolate anion, 47, as the product. Remember from Chapter 22 (Section 22.7.4) that the a-proton of a 1,3-dicarbonyl compound such as diethyl malonate is rather acidic (pK of about 11), and even a relatively weak base will deprotonate to form the enolate anion. Michael addition of 46 with ethyl acrylate will give enolate anion 47, and aqueous acid workup leads to the isolated product, 48. Attack at the -carbon is possible because that carbon is less hindered than the acyl carbon, so reaction at the C=C unit is somewhat faster than attack at the acyl carbon. Michael addition occurs with relatively stable carbanion nucleophiles, such as malonate derivative 46 and some other common nucleophiles. Other conjugated carbonyl derivatives react similarly. 

Attack on Unsaturated Carbon.- Tervalent phosphorus compounds are effective catalysts for the polymerization of acrylic acid derivatives, and the monomeric adducts which initiate the polymerization usually cannot be isolated. However, by addition of ethyl 2-cyanoacrylate to strongly nucleophilic tervalent phosphorus compounds it was possible to isolate monomeric adducts,... 

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