Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: azmanam on November 30, 2009, 08:21:54 AM
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Very fun transformation this week. I've provided the (yes, desired) product of this tandem transformation.
QUESTION: Provide the mechanism and name the two named reactions in this tandem transformation
EDIT: Structure fixed to correct misdrawn product
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I want to make sure wether the two OMe goups were missed by you in the product :)
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thank you. yes, the final product should still have the two OMe groups... silly error. We are not doing a bis demethoxylation. That would truly be remarkable. Good catch :) I've fixed it in the op
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I think the you meant 1)Ac2O 2)TsOH
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Here's an idea, I haven't really used the TsOH and I have a really dodgy conversion of the hemithioacetal -> ketone in the absence of water (or can I assume the TsOH is the monohydrate?)
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Heory, I like your order of reactions better. The ketone formation in yours makes alot more sense than in mine. A couple of things though, I think you lost a carbon when you formed the beta-lactam (should be gamma I think), and your arrows for addition of the enolate to the iminium ion are the wrong way round.
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haha. we post almost at the same time. Two very different ways... Insteresting
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Oh my god. Yes, dan. I was reviewing chapter of antibotics in my text book this evening which made me think it's a beta-lactam.
correction:
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I would call the last bit a Pictet–Spengler reaction rather than a Friedel–Crafts.
Also, if you draw a different resonance structure, then the first cycloaddition can be called a Diels–Alder.
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Hello!Dan! i agree with your steps except the sulfur ylide make the addition to the ester group.Heory's 1,3 dipole cycloaddition is more better.but other steps is so excellent! i feel excited about your mechanism.When i read this question,i am wondering why the nucleophlie must attack the same face as the -COOMe?Could you explain it in more details?
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Calculated by computer, the trans-substituted lactam has the energy 63kJ/mol more than the cis-substituted one.
I think the cylohexone ring is hard to twist because 3 bonds should be at the same plane due to the aryl ring.
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Heory get's it right this week. I thought the mechanism might be too ambiguous without the product, but perhaps it was too straightforward with the product given?
I'd also call the cycloaddition a Diels-Alder, but they're just resonance structures of each other, right? The neutral resonance structure is probably the better resonance contributor, but the dipolar cycloaddition is still a resonance structure. The reaction is drawn in the papers as a Diels Alder.
This is methodology from the Padwa group as an entry into the Erythrinane family. Nice work, imho.
http://dx.doi.org/10.1021/jo9716183
http://dx.doi.org/10.1016/0040-4039(95)00574-V
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Hello!Heory,i think the three bonds should be at the same plane,but why the cis lactam is more favor than the trans lactam?