Since it’s a ketone, we can use a strong base to convert it into an enolate: Once we have an enolate, we can add the other reagent to it to go through the Michael Addition: Finally, once we have our Michael addition product, we need to finish this Robinson Annulation cascade by doing an intramolecular aldol condensation: This sequence assembles the carbon skeleton for our molecule. conversion to continue: The subsequent cyclization via Aldol Addition We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. After completing this section, you should be able to. write an equation to illustrate the Robinson annulation reaction. six-membered rings in polycyclic compounds, such as steroids. polymerization. Thus, when asked how such a compound might be prepared, you should keep the possibility of using a Robinson annulation reaction in mind. 51C Practice Problems 8 Spring, 2015 1. a. Let’s try a normal polarity approach for this problem and see what we get. The final reduction gives us the target molecule! O O EtO Br Br NaOEt O H3O+, heat EtO-CO2 O EtO OEt 1. Robinson Annulation is a useful reaction for the formation of So, without a further ado, here’s the question: Propose the reasonable synthetic sequence to accomplish the following transformation—. 2. Now, when we have figured out the reagents (synthetic equivalents), it’s time to put it all together. Missed the LibreFest? A complex sequence that can be used to form bicyclic systems containing a substituted cyclohexenone system. Your email address will not be published. Find what has changed. Typically, when we are thinking about the C-nucleophiles, we’re talking about various organometallic compounds, or enols/enolates. So, without a further ado, here’s the question: Propose the reasonable synthetic sequence to accomplish the following transformation— While this synthesis may look intimidating, let’s break the whole process into small steps. It combines two reactions: the The next step is to come up with what we call a “synthon.” Synthons are the molecular entities which don’t have to be “real” molecules but rather are scaffolds of molecules with the correct charges on atoms. steady-state concentration of enone and decrease the side reaction of entire process occurring in one pot, as shown below. Ring-forming reactions are called annulations after the Latin work for ring annulus. Michael Addition, The The use of a precursor of He received the Nobel prize in chemistry in 1947. The building of an alicyclic compound from acyclic starting materials can present an interesting challenge to the synthetic organic chemist. Lett., 1971, 12, 4995. Likewise, if you have a minus on your C, you’re dealing with some sort of a nucleophilic species. You could also perform the Robinson annulation in acidic conditions as a single pot reaction. Did you make any functional group transformations? Related Reactions By assigning the negative charge to the oxygen atom and alternating it from atom to atom we get the following picture. While there are other possibilities, these are the most typical examples you’ll normally see in your course.[transition]. Provide a mechanism for the following Claisen condensation: O CH3 OCH2CH3 OO CH3COCH2CH3 NaOEt HOEt b. Ethoxide ion is used as the base in the condensation above to avoid some unwanted reactions. The complex hydrides are, however, less regioselective and occasionally don’t work for a complete reduction like the one we want to perform, so I’m choosing a “foolproof” way here, although it does require harsher conditions than you would expect in a regular reduction with hydrogen gas. These two molecules can react with each other under basic conditions in a reaction we know as Robinson Annulation. This is my first post on synthesis, I’ll also do a brief introduction to the retrosynthetic analysis. In the second step, the Michael adduct undergoes an intramolecular aldol reaction to give cyclic α,β-unsaturated ketones. NaOEt 2. Or, alternatively, they can be easily converted to reactive intermediates with the required charges. He's the founder and director of. Required fields are marked *, Victor is a professional chemical educator and researcher, organic chemistry tutor, and an academic coach from Colorado Rocky Mountains. The Robinson Annulation reaction. identify the cyclic product formed when a 1,5‑diketone is treated with base. Summary. the α,β-unsaturated ketone, such as a β-chloroketone, can reduce the NaOEt 2. Both of these steps involve attack by enolate anions. So, what’s going to be our first step? While this synthesis may look intimidating, let’s break the whole process into small steps. The first step in the Robinson annulation is a Michael reaction to form a 1,5-dicarbonyl compound. identify the carbonyl compounds and any other reagents needed to synthesize a given cyclic compound by a series of reactions, one of which is a Robinson annulation. So, looking at our synthons and thinking a little about all different possibilities, we can come up with the two molecules: a carbonyl compound (which happens to be our starting material) and an α,β-unsaturated ketone. Essentially, if you have a plus, it’s an electrophile, so you should be thinking about what sort of a molecule you can come up with that has the same skeleton and is electrophilic. There are two ways how you can find those charges: normal polarity and the reversed polarity method. Advanced enol and enolate chemistry. Remember that during annulations five and six membered rings are preferred. First, we’ll need to make a good nucleophile out of our starting material. 1) Fill in the details of reagents and conditions above each arrow. write an equation to illustrate the Robinson annulation reaction. Title: PS#4_answer key Author: Hof Created Date: 1/26/2010 5:12:50 PM a) C. H. Heathcock, J. E. Ellis, J. E. McMurry, A. Coppolino, Tetrahedron

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