Radical Cyclization of Haloacetals: The Ueno-Stork Reaction

Salom‐Roig, Xavier J.; Dénès, Fabrice; Renaud, Philippe

doi:10.1055/s-2004-831161

“…Hydrogen atom abstraction from the solvent was excluded by conducting the reaction in a mixture of thf- d 8 and C 6 D 6 (see Figure ). Classically, radical cyclizations of this type (the so-called Ueno–Stork cyclizations) are carried out at elevated temperatures using a combination of AIBN and Bu 3 SnH. Employing the methodology reported herein, crude 6 is generated at room temperature without relying on toxic tin reagents.…”

Section: Resultsmentioning

confidence: 99%

Coordination-Induced Radical Generation: Selective Hydrogen Atom Abstraction via Controlled Ti–C σ-Bond Homolysis

Mörsdorf,

Ballmann

2023

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A method for the generation of transient alkyl radicals via homolytic Ti−C bond cleavage was developed by employing a tailor-made organotitanium half-cage complex. In contrast to established metal-mediated radical initiation protocols via thermal or photochemical M−C σ-bond homolysis, radical formation is triggered solely by coordination of a solvent molecule (thf) to a titanium(IV) center. During the reaction, the nonstabilized alkyl radical is formed along with a persistent titanium(III) metalloradical, thus taming the former transient radical (persistent radical effect). Radical coupling and hydrogen atom abstraction (HAT) reactions have been explored not only experimentally but also computationally and by means of kinetic analysis. Exploiting these findings led to the development of selective HAT transformations, for example, with 9,10-dihydroanthracene. Deuterium labeling studies using selectively deuterated alkyls and 9,10-dihydroanthracene-d 4 confirmed a radical pathway, which was underpinned by developing a radical−radical crosscoupling reaction for transferring the alkyl radical to a stable Sn-centered radical. To set the stage for an application in organic synthesis, a 5-endo-trig radical cyclization based on our methodology was established, and a dihydroxylated sesquiterpene was thus prepared in high diastereomeric excess.

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“…This process proved to be successful and high-yielding with a range of representative substrates, including highly acid-sensitive precursors. "This is a significant advance compared to the classical cyclization of SYNFORM, 2010/03 Published online: 18.02.2010, DOI: 10.1055/s-0029-1219445 7 which requires the use of either Lewis or Brønsted acidic conditions for the conversion of the cyclic acetals into the corresponding lactols," said Dr. Dénès. "This very mild approach to γ-lactols allows solving the problem of chemoselectivity encountered for the hydrolysis of cyclic acetals obtained by cyclization of α-halo acetals and we expect our methodology to be embraced by many synthetic chemists in the field of total synthesis," they concluded.…”

Section: G-h Leementioning

confidence: 99%

SYNFORM ISSUE 2010/03

Zanda¹

2010

Synfacts

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Yo ur op ini on ab ou t SY NF OR M is we lco me , ple as e co rre sp on d if yo u lik e: ma rk et ing @t hie me -c he mi str y.c omThis document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. Dear readers,Do you like good food? I would guess the answer is a unanimous yes. But what is "good food"? Here I am afraid we would not have a unanimous answer, although some degree of agreement is expected in some cases. For example, most of you would recognize Italian "lasagne", French "crepes" and Japanese "sushi" as delicious. However, it all comes down to the personal taste because some others like Scottish "haggis" or French "escargots" or Italian "trippa" which personally I don't find particularly attractive... Let's take a globalized, apparently very simple food like pizza. What makes a good pizza? Have you ever tried a wood fired oven baked "pizza margherita" in a typical restaurant in the Naples area? It's an extremely simple, yet delicious food, and what makes it really fantastic is the combination of a handful of basic ingredients: mozzarella and tomato on a fragrant layer of pizza bread, with a few basil leaves (personally I love to add a few drops of good "extravergine" olive oil). You don't need many sophisticated or unusual toppings to make a fantastic pizza, just the combination of two or three simple, well-chosen and tasty ingredients. Are you hungry now? If yes, you might want to have a good pizza tonight for dinner, but let me just conclude my thought before heading to a pizzeria. Personally, I am convinced that, like a good pizza comes from simple ingredients cooked in just five minutes, a brilliant idea comes from the combination of few simple and linear thoughts which simultaneously enter your mind at the right moment and come out as a flash of genius. Simplicity is the key, for good food as well as for good ideas! And if you can resist a few more minutes before biting your well deserved pizza, you might want to have a look at this new issue of SYNFORM which is full of tasty and creative chemistry. The first SYNSTORY is about a novel enantioselective organocatalytic cyclization process developed by B.-C. Hong (Taiwan). The second SYNSTORY deals with a synthetically very useful radical cyclization reported by J. Lebreton and F. Dénès (France). Last but certainly not least, the fascinating organometallic synthesis of long helicenes reported by I. Stary (Czech Republic).Enjoy your pizza! Pardon, your reading... Cascade reactions are extremely attractive in terms of synthetic efficiency, particularly when they allow for the preparation of complex structures with good stereochemical control. Recently, Professor Bor-Cherng Hong and his coworkers from the National Chung Cheng University (Taiwan) have discovered a novel organocatalytic enantioselective cascade nitro-Michael-Michael-Wittig reaction involving a dynamic kinetic asymmetric transformation. This annulation reaction provides a simple and direct protocol for the stereoselective construction of trisubstituted ...

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“…This process proved to be successful and high-yielding with a range of representative substrates, including highly acid-sensitive precursors. "This is a significant advance compared to the classical cyclization of SYNFORM, 2010/03 Published online: 18.02.2010, DOI: 10.1055/s-0029-1219529 7 which requires the use of either Lewis or Brønsted acidic conditions for the conversion of the cyclic acetals into the corresponding lactols," said Dr. Dénès. "This very mild approach to γ-lactols allows solving the problem of chemoselectivity encountered for the hydrolysis of cyclic acetals obtained by cyclization of α-halo acetals and we expect our methodology to be embraced by many synthetic chemists in the field of total synthesis," they concluded.…”

Section: G-h Leementioning

confidence: 99%

“…Ed. 2009, 48, 9549-9552 α-halo acetals (the Ueno-Stork reaction) 7 which requires the use of either Lewis or Brønsted acidic conditions for the conversion of the cyclic acetals into the corresponding lactols," said Dr. Dénès. "This very mild approach to γ-lactols allows solving the problem of chemoselectivity encountered for the hydrolysis of cyclic acetals obtained by cyclization of α-halo acetals and we expect our methodology to be embraced by many synthetic chemists in the field of total synthesis," they concluded.…”

Section: Synstories A27mentioning

confidence: 99%

Synform Issue 2010/03

Zanda¹

2010

Synlett

0

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Yo ur op ini on ab ou t SY NF OR M is we lco me , ple as e co rre sp on d if yo u lik e: ma rk et ing @t hie me -c he mi str y.c omThis document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. Dear readers,Do you like good food? I would guess the answer is a unanimous yes. But what is "good food"? Here I am afraid we would not have a unanimous answer, although some degree of agreement is expected in some cases. For example, most of you would recognize Italian "lasagne", French "crepes" and Japanese "sushi" as delicious. However, it all comes down to the personal taste because some others like Scottish "haggis" or French "escargots" or Italian "trippa" which personally I don't find particularly attractive... Let's take a globalized, apparently very simple food like pizza. What makes a good pizza? Have you ever tried a wood fired oven baked "pizza margherita" in a typical restaurant in the Naples area? It's an extremely simple, yet delicious food, and what makes it really fantastic is the combination of a handful of basic ingredients: mozzarella and tomato on a fragrant layer of pizza bread, with a few basil leaves (personally I love to add a few drops of good "extravergine" olive oil). You don't need many sophisticated or unusual toppings to make a fantastic pizza, just the combination of two or three simple, well-chosen and tasty ingredients. Are you hungry now? If yes, you might want to have a good pizza tonight for dinner, but let me just conclude my thought before heading to a pizzeria. Personally, I am convinced that, like a good pizza comes from simple ingredients cooked in just five minutes, a brilliant idea comes from the combination of few simple and linear thoughts which simultaneously enter your mind at the right moment and come out as a flash of genius. Simplicity is the key, for good food as well as for good ideas! And if you can resist a few more minutes before biting your well deserved pizza, you might want to have a look at this new issue of SYNFORM which is full of tasty and creative chemistry. The first SYNSTORY is about a novel enantioselective organocatalytic cyclization process developed by B.-C. Hong (Taiwan). The second SYNSTORY deals with a synthetically very useful radical cyclization reported by J. Lebreton and F. Dénès (France). Last but certainly not least, the fascinating organometallic synthesis of long helicenes reported by I. Stary (Czech Republic).Enjoy your pizza! Pardon, your reading... Cascade reactions are extremely attractive in terms of synthetic efficiency, particularly when they allow for the preparation of complex structures with good stereochemical control. Recently, Professor Bor-Cherng Hong and his coworkers from the National Chung Cheng University (Taiwan) have discovered a novel organocatalytic enantioselective cascade nitro-Michael-Michael-Wittig reaction involving a dynamic kinetic asymmetric transformation. This annulation reaction provides a simple and direct protocol for the stereoselective construction of trisubstituted ...

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Radical Cyclization of Haloacetals: The Ueno-Stork Reaction

Cited by 29 publications

References 191 publications

Coordination-Induced Radical Generation: Selective Hydrogen Atom Abstraction via Controlled Ti–C σ-Bond Homolysis

Coordination-Induced Radical Generation: Selective Hydrogen Atom Abstraction via Controlled Ti–C σ-Bond Homolysis

SYNFORM ISSUE 2010/03

Synform Issue 2010/03

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