Silver-Catalyzed Cyclization of Sulfonyl Allenes to Dihydrofurans.
TL;DR: Treatment of α-hydroxy allenic sulfones with 10 mol % of silver fluoride in acetonitrile at ambient temperature furnished the corresponding 3-tosyl 2,5-dihydrofurans in excellent yields via a 5-endo-trig cyclization.
About: This article is published in Organic Letters.The article was published on 2016-10-27. It has received 24 citations till now. The article focuses on the topics: Sulfonyl & Silver fluoride.
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TL;DR: The most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products, are summarized in this paper.
Abstract: The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.
95 citations
TL;DR: By employing CuOAc as the catalyst, this article realized a four-component reaction of 1,3-enynes, diselenides, DABCO·(SO2)2, and cycloketone oxime esters, providing facile access to diverse cyanoalkylsulfonylated allenyl selenides in moderate to good yields.
44 citations
TL;DR: Regio- and enantioselective annulation between β,γ-unsaturated α-keto esters and non-activated allenes was achieved by using a chiral cationic indium(III)/phosphate catalyst.
Abstract: Regio- and enantioselective [4+2] annulation between β,γ-unsaturated α-keto esters and non-activated allenes was achieved by using a chiral cationic indium(III)/phosphate catalyst. The reaction affords the corresponding C3-selective dihydropyrans in good yields and with high enantioselectivity (up to 99 % ee).
38 citations
TL;DR: Allenyl sulfones are versatile building blocks that readily partake in a variety of transformations such as Michael additions, rearrangements, cycloadditions, electrophilic additions and redox reactions.
Abstract: Allenyl sulfones are versatile building blocks that readily partake in a variety of transformations such as Michael additions, rearrangements, cycloadditions, electrophilic additions and redox reactions. Selected recent developments in the preparation and various reactions of allenyl sulfones are presented.
22 citations
TL;DR: In this paper, a conjugate addition and 5-endo-trig cyclization reaction of 3-cyclopropylideneprop-2-en-1-ones with sodium sulfinates in the presence of iodine is described.
Abstract: A highly efficient conjugate addition and 5-endo-trig cyclization reaction of 3-cyclopropylideneprop-2-en-1-ones with sodium sulfinates in the presence of iodine is described. A wide variety of densely functionalized 3-sulfonylfurans are furnished by single-step and one-pot methods, respectively. The results of such postcyclization modifications are also presented.
18 citations
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TL;DR: This Review draws on experimental and computational data to present the current understanding of homogeneous gold catalysis, focusing on previously unexplored reactivity and its application to the development of new methodology.
Abstract: Transition-metal catalysts containing gold present new opportunities for chemical synthesis, and it is therefore not surprising that these complexes are beginning to capture the attention of the chemical community. Cationic phosphine-gold(i) complexes are especially versatile and selective catalysts for a growing number of synthetic transformations. The reactivity of these species can be understood in the context of theoretical studies on gold; relativistic effects are especially helpful in rationalizing the reaction manifolds available to gold catalysts. This Review draws on experimental and computational data to present our current understanding of homogeneous gold catalysis, focusing on previously unexplored reactivity and its application to the development of new methodology.
1,534 citations
TL;DR: This account comprises gold-catalyzed cyclization reactions of allenes by attack of carbon or heteroatom nucleophiles, which are particularly well suited for the selective activation of allene in the presence of other reactive functionalities.
Abstract: Allenes are highly valuable synthetic precursors in preparative organic chemistry because of their ability to undergo a variety of transformations. Among many different reaction modes, activation of the cumulated double bonds by treatment with a Brønsted or Lewis acid is particularly useful because it allows a nucleophilic attack, which leads to the formation of a new C-C or Cheteroatom bond in an interor intramolecular fashion. Because of their axial chirality, allenes can undergo this bond formation with chirality transfer, which renders the method attractive for stereoselective target-oriented synthesis. Because of their soft and carbophilic character, gold catalysts are particularly well suited for the selective activation of allenes in the presence of other reactive functionalities. Compared to intermolecular additions, gold-catalyzed cyclization reactions of allenes by intramolecular nucleophilic attack have received much more attention. Here, the gold catalyst can coordinate to either allenic double bond, and the regioselectivity of the subsequent nucleophilic attack depends on the structure of the substrate, in particular the length of the tether connecting allene and nucleophile (Scheme 1). Hence, four different endoor exo-cyclization products can be obtained, but the formation of fiveor sixmembered rings via σ-gold species A or D, i.e., by nucleophilic attack at a terminal allenic carbon atom, is favored in most cases, whereas products arising from nucleophilic attack at the central allenic carbon atom (via intermediates B and C) are rare. Normally, these cyclization products are chiral and can be accessed in a stereoselective manner either from chiral allenes by axis-to-center chirality transfer or from achiral allenes utilizing chiral gold catalysts. This account comprises gold-catalyzed cyclization reactions of allenes by attack of carbon or heteroatom nucleophiles. Intermolecular addition reactions to allenes, as well as gold-catalyzed transformation of nonallenic substrates in which an allene is generated in situ (e.g., by sigmatropic rearrangement) and converted without isolation, will not be covered.
1,002 citations
TL;DR: This Review pays attention to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts.
Abstract: Allenes are the simplest class of cumulenes, with two contiguous CC bonds, and show unique physical and chemical properties. These features make allenes particularly attractive in modern organic chemistry. In this Review, attention is paid to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts. Their versatile reactivity, substituent-loading ability, axial to center chirality transfer, and controllable selectivity allow access to target molecules by unique and efficient approaches. The main topics in this Review are presented with selected examples from 2003 to 2011.
746 citations
385 citations
TL;DR: It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively, in haloallenyl ketones.
Abstract: Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively. Halirenium intermediate was proposed for the unusual 1,2-halogen migration. This cascade transformation allows for mild and efficient synthesis of various types of 3-halofurans.
315 citations