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This question was a result of discussion form here: α,β-unsaturated carbonyl compounds and alkyl addition

The reaction below (condensation of cyclohexenone with a secondary amine) does not yield any results on a literature search, even when I only search for the product by itself (unless my search was not good enough):

Enamine formation from cyclohexenone

Can enamines actually be formed from α,β-unsaturated ketones? If not, what prevents it from being possible?

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  • $\begingroup$ These two references concern the photoaddition of amines to benzene, not the addition to cyclohexenone. Enamine formation of cyclohexenone itself may be problematic but dienamines of enones have been reported. I'll put up an answer $\endgroup$ – user55119 Jul 28 '18 at 22:41
  • $\begingroup$ @user55119 You are right, i made a daft mistake in placing the double bond. I corrected it now and removed the now irrelevant references. $\endgroup$ – AMM Jul 29 '18 at 8:01
  • $\begingroup$ Did find this one: pubs.rsc.org/en/Content/ArticleLanding/2016/RA/…, but it is computational only not synthetic. $\endgroup$ – AMM Jul 29 '18 at 8:10
  • $\begingroup$ I'm not sure to what extent conjugate addition to the enone competes with enamine formation. At least, that's the first reaction I'd think of when I see amine + enone. Removing water will probably favour enamine formation if there's an equilibrium being established, which is probably why user55119's example has toluene+reflux (which I interpret to be a Dean-Stark setup). Morpholine boils at 129 °C which helps (toluene at 111 °C). $\endgroup$ – orthocresol Jul 29 '18 at 9:18
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Stork and Birnbaum have reported (Tetrahedron Lett. 1961, 10, 313) the formation of dienamine 2 from octalone 1. Alkylation with methyl iodide leads to α-alkylation of the dienamine. Buffer conditions are required for hydrolysis of the dienamine to octalone 4.

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  • $\begingroup$ This is a good answer but i think it fits really well with the original question (chemistry.stackexchange.com/questions/57494/…) as a special occasion where an α,β unsaturated ketone can actually form the enamine which then alkylates. I suggest to move this answer there. It doenst fit here that much since this question refers to formation (or not) of the imine 1 in the question. I also made a mistake in the question above, now corrected, which may have confused you, sorry. $\endgroup$ – AMM Jul 29 '18 at 7:59
  • $\begingroup$ You should correct the enamine reaction with methyl vinyl ketone (MVK) at chemistry.stackexchange.com/questions/57494/…. The reaction continues to give the dienamine of the aldol condensation product (Cf., 2 above). Perhaps using acrylonitrile rather than MVK would eliminate the issue of the aldol step. After addition, the less substituted enamine is formed. $\endgroup$ – user55119 Jul 29 '18 at 14:18
  • $\begingroup$ Ok, i made the reaction more general. Also referenced your reply here since although the reaction doenst seem to be reported with pyrrolidine, in general it is possible to add alkyl groups in α,β-unsaturated carbonyl compounds by using secondary amines. Lastly, compounds like 1 above, namely 2 amido dienes can be formed but their synthesis seems more involved according to this: Beilstein J. Org. Chem. 2011, 7, 410–420. doi:10.3762/bjoc.7.53. Not sure why though, which is the actual question! $\endgroup$ – AMM Jul 29 '18 at 18:16

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