Stabilized carbon nucleophiles enones

There is also a frontier orbital effect that assists conjugate addition over the aldol reaction, You will reeall that the carbonyl carbon is a relatively hard centre, whereas the 3 carbon of an enone is soft, As the nucleophilic enolate becomes more stabilized with extra electron-withdrawing groups, it beeomes increasingly soft and hence more likely to attack the [J carbon,... 

Selenium-stabilized carbanions behave as excellent nucleophiles and react with primary alkyl bromides or iodides, allylic and benzylic bromides, epoxides, oxeta-nes, disulfides, trialkylsilyl chlorides, aldehydes, ketones, carbon dioxide, dime-thylformamide, acid chlorides or alkyl chloroformates. With conjugated enones, in the presence of HMPA as cosolvent, the 1,4-addition product is essentially obtained. 

Lewis acid complexes of -substituted a, 3-unsaturated ketones and aldehydes are unreactive toward alkenes. Crotonaldehyde and 3-penten-2-one cannot be induced to undergo ene reactions like acrolein and methyl vinyl ketone. The presence of a substituent on the -carbon stabilizes the enal- or enone-Lewis acid complex and stericdly retards the approach of an alkene to the -carbon. However, Snider et al. have found that a complex of these ketones and aldehydes with 2 equiv. of EtAlCk reacts reversibly with alkenes to give a zwitterion (22). This zwitterion, which is formed in the absence of a nucleophile, reacts reversibly to give a cyclobutane (23) or undergoes two 1,2-hydride or alkyl shifts to generate irreversibly a p, -disubstituted-a,P-unsaturated carbon compound (24). 

In this case, diethylenetriamine acts as a trinucleophile its interaction with amino enone 71 involves double nucleophilic addition at the /1-carbon, forming ammonia, and an attack at the carbonyl group, liberating water. The reaction takes place when the compound contains a polyfluoroalkyl substituent, not only enhancing the electrophilicity of the /1-carbon atom, but also stabilizing the imidazolidine ring. 

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