I have recently come across this organic chemistry problem. enter image description here I thought it would undergo simple Diels–Alder reaction enter image description here But it didn't turn out to be. The product to me looks like a nucleophilic attack of (I) on (II). Can anybody say me why exactly this abnormality seen and what is the mechanism of this reaction?

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    $\begingroup$ You're not going to achieve a s-cis conformation for a [4+2] cycloaddition. The dithiide protecting group is way too bulky to be in plane with the vinyl ether. This is a conjugate addition into the enone, followed by aromatization of the ring, and addition of the phenol moiety into the oxocarbenium. $\endgroup$ – Zhe Oct 3 '17 at 17:52
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    $\begingroup$ I thought about the bulkiness of the dithiane group but I couldn't get any further ideas. Can you please put up the solution. $\endgroup$ – Suraj S Oct 3 '17 at 17:58
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    $\begingroup$ You should have enough hints from my first comment. Please think about the requirements for a [4+2] cycloaddition and the implications thereof. Build models if necessary. $\endgroup$ – Zhe Oct 3 '17 at 18:11
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    $\begingroup$ I suggest editing the title. As it stands now, it is misleading. See, there is a thing called inverse electronic demand D.-A., and that's an abnormal Diels-Alder reaction for sure. Yours is not a Diels-Alder at all. $\endgroup$ – Ivan Neretin Oct 3 '17 at 18:33
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    $\begingroup$ @IvanNeretin an inverse electron demand DA is not abnormal. Diene + dienophile leading to a cyclohexene derivative is a DA reaction, doesn't matter what's the mechanism. $\endgroup$ – DSVA Oct 4 '17 at 10:08

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