Search

A sequential phosphine‐catalyzed asymmetric [3+2] annulation of aldimines with allenoates and oxidative central‐to‐axial chirality transfer strategy has been developed. This approach is operationally simple, allowing for rapid access to a range of axially chiral CF3‐containing 2‐arylpyrroles with high enantiomeric excess. Furthermore, an atroposelective synthesis of esaxerenone is presented, illustrating the practical potential of the reported method. [ABSTRACT FROM AUTHOR]

A phosphine‐catalyzed highly enantioselective and diastereoselective (up to 98 % ee and >20 : 1 dr) (3+2) annulation between vinylcyclopropanes and N‐tosylaldimines has been developed, which allows facile access to a range of highly functionalized chiral pyrrolidines. Notably, this method makes use of vinylcyclopropanes as a synthon for phosphine‐mediated asymmetric annulation reaction, which will offer new opportunities for potential applications of cyclopropanes substrates in phosphine‐catalyzed organic transformations. [ABSTRACT FROM AUTHOR]

The past two decades have witnessed remarkable growth of asymmetric organocatalysis, which is now a firmly established synthetic tool, serving as a powerful platform for the production of chiral molecules. Ring structures are ubiquitous in organic compounds, and, in the context of natural product synthesis, strategic construction of ring motifs is often crucial, fundamentally impacting the eventual fate of the whole synthetic plan. In this review, we provide a comprehensive and updated summary of asymmetric organocatalytic annulation reactions; in particular, the application of these annulation strategies in natural product synthesis will be highlighted. [ABSTRACT FROM AUTHOR]

[Display omitted] A tandem reaction of 2-aminonaphthoquinone/4-aminocoumarins with 1,3-diarylpropenes mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)/ tert -butyl nitrite (TBN)/O 2 is disclosed. It involves oxidative coupling, intramolecular annulation and dehydro-aromatization reaction, which provides an efficient and mild method for the synthesis of 1-aza-anthraquinones and pyridocoumarins. [ABSTRACT FROM AUTHOR]

Construction of contiguous all‐carbon quaternary stereogenic centers is a long‐standing challenge in synthetic organic chemistry. In this report, a phosphine‐catalyzed enantioselective (3+2) annulation reaction between allenes and isoindigos, containing either two identical or different oxindole moieties, is introduced as a powerful strategy for the construction of spirocyclic bisindoline alkaloid core structures. The reported reactions feature high chemical yields, excellent enantioselectivities, and very good regioselectivities, and are highly useful for creating structurally challenging bisindoline natural products. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The first highly enantioselective phosphine-catalyzed formal [4+4] annulation has been developed. In the presence of amino-acid-derived phosphines, the unprecedented [4+4] annulations between benzofuran/indole-derived α,β-unsaturated imines and allene ketones proceeded smoothly, thus affording azocines, bearing either a benzofuran or an indole moiety, in excellent yields and with nearly perfect enantioselectivities (≥98 % ee in most cases). This work marks the first efficient asymmetric construction of optically enriched eight-membered rings by phosphine catalysis. [ABSTRACT FROM AUTHOR]

Phosphine-catalyzed enantioselective annulation reactions involving ketimines are a daunting synthetic challenge owing to the intrinsic low reactivity of ketimine substrates. A highly enantioselective [3+2] cycloaddition reaction that makes use of isatin-derived ketimines as reaction partners was developed. Notably, both simple and γ-substituted allenoates could be utilized, and various 3,2′-pyrrolidinyl spirooxindoles with a tetrasubstituted stereocenter were obtained in excellent yields and with nearly perfect enantioselectivity (>98 % ee in all cases). [ABSTRACT FROM AUTHOR]

An enantioselective synthesis of spiropyrazolones from allenoate-derived MBH acetates and pyrazolones through a phosphine-mediated [4+1] annulation process has been developed. Spiropyrazolones were readily prepared in good chemical yields and good to high enantioselectivities. This is the first asymmetric example in which α-substituted allenoates were utilized as a C4 synthon for phosphine-catalyzed [4+1] annulation. [ABSTRACT FROM AUTHOR]

Chemical equations for the article "Enantioselective Annulation of α-Substituted Allenoates with β,γ-Unsaturated N-Sulfonylimines Catalyzed by a Bifunctional Dipeptide Phosphine", by H. Ni and others, published in "Beilstein Journal of Organic Chemistry" in 2016 are presented.

An enantioselective [4 + 2]-annulation process between cyano-activated oxadienes and allenones is developed. An l-valine-derived phosphine was efficient in catalyzing the reaction, and a wide range of highly functionalized dihydropyrans were prepared in high yields and with excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

A novel [4 + 2] annulation process is developed employing β,γ-unsaturated α-keto esters as C4 building blocks and allene ketones as C2 synthons. [ABSTRACT FROM AUTHOR]

The optimized conditions including a L-valine-derived phosphine catalyst (PAM) allow the synthesis of a wide variety of dihydropyrans in high yields and excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

The title synthesis represents the first asymmetric application of α-substituted allenoates in [4 + 1] annulation. [ABSTRACT FROM AUTHOR]