Photochemical transformations of small ring compounds. 92. Intramolecular dipolar cycloaddition reactions with vinylbiphenyl-substituted 1,3-dipoles

Padwa, Albert; Ku, Hao; Mazzu, Arthur

doi:10.1021/jo00397a001

Cited by 19 publications

(1 citation statement)

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“…Compounds with the 1 H -dibenzo[ e,g ] indole framework have shown interesting electronic properties 12–15 and potential medicinal applications. 15–17 Hence, several routes were developed for their synthesis, including electrocyclization of 2-(cyclohex-1-enyl)-3-phenyl-4-nitropyrrole, 7 sequential Suzuki–Miyaura cross-couplings, followed by metal-assisted C–N cyclization, 12 thermolysis of methyl-2-azido-3-(phenanthrene-9-yl)acrylate, 15–17 arylation of 3-(2-chlorophenyl)pyrrole, followed by C–H annulation under Pd-catalysis, 18 intramolecular 1,3-dipolar cycloaddition of 2′-substituted-2-vinylbiaryls, 19 Fischer cyclization of the hydrazone obtained from 9-phenanthrylhydrazine and pyruvic acid/ester, 20 Pd-catalyzed annulative π-extension of pyrroles with diiodobiaryls, 21 and Pd-catalyzed C–H annulation of 3-phenylpyrrole with 1,2-dibromobenzene or 3-bromopyrrole with 2-bromobiphenyl. 13 Although all of these routes have special merits, some are limited by low yields, require multi-step reactions, or need expensive substrates.…”

Section: Introductionmentioning

confidence: 99%

A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

et al. 2022

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Section: Introductionmentioning

confidence: 99%

A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

et al. 2022

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The [3 + 2] Nitrone–Olefin Cycloaddition Reaction

1988

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Early researchers studying the condensation product of carbonyl compounds with N ‐substituted hydroxylamines elected to coin the term “nitrone” as a combination of the words “nitrogen” and “ketone.” This was done to emphasize the parallel between this newly discovered functionality and the already rich chemistry of the carbonyl group. For example, nitrones are capable of reacting with carbanions of various types, a consequence of the iminium species embedded in the nitrone that renders the functionality susceptible to nucleophilic attack. Thus C ‐phenyl‐ N ‐methylnitrone undergoes a Reformatsky reaction with ethyl bromoacetate in complete analogy with benzaldehyde. The intermediate zinc alkoxide cyclizes to 2‐methyl‐3‐phenylisoxazolidin‐5‐one, a type of compound that can also be prepared by the related nucleophilic addition of dialkyl malonates to nitrones. This chapter deals with a unique property of nitrones not shared by the corresponding carbonyl compounds, namely, a marked ability to undergo a [3 + 2] cycloaddition reaction in the presence of a dipolarophile. The reactions of nitrones with substituted olefins, both intermolecular and intramolecular are addressed. This process yields isoxazolidines directly, affording products related to those obtained in the Reformatsky reaction but arising by a different reaction mode. The intent of the review presented in this chapter is to provide a thorough understanding of the nitrone–olefin [3 + 2] cycloaddition reaction and to illustrate its power by describing some significant applications to complex synthetic problems. Various aspects have been reviewed. This documentation of the nitrone–olefin cycloaddition reaction begins with the preparation and stability of the nitrone component and is followed by mechanistic considerations. A presentation of the dipolarophile syntheses is beyond the scope of this chapter; however, the tabular survey provides leading references to specific examples. The important concepts of regio‐ and stereo‐selectivities are introduced next. Since the general rules of regiochemistry that apply in the intermolecular version of the reaction are often reversed in the intramolecular version, the latter are dealt with separately. Finally, important applications to the total synthesis of natural products are presented. The versatile utility of the nitrone–olefin cycloaddition reaction in the synthesis of natural products has been the major driving force in the development of this long‐neglected chemistry. An in‐depth understanding of the key transformations of the isoxazolidines afforded by the reaction will place this chemistry firmly within the arsenal of organic reactions.

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The Oxidation of Alcohols by Modified Oxochromium( VI )–Amine Reagents

Luzzio

1998

Organic Reactions

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The development of oxochromium(VI)‐amine reagents as oxidants in organic synthesis has evolved since the early studies of Sisler which described the use of adducts of heterocyclic nitrogen bases and chromium(VI) oxide. The later work of Sarrett and coworkers in steroid synthesis soon established the utility of chromium(VI) oxide‐pyridine adducts as the first selective oxochromium(VI)‐amine reagents. Several modifications of the Sarrett oxidation followed. The present concern with the toxicity and environmental implications of oxochromium(VI) has provided encouragement for the study and use of catalytic oxochromium reagents in conjunction with stoichiometric co‐oxidants such as peroxides. Such technology is welcome, particularly when applied to the large‐scale preparations found in industry where the disposal of byproducts is a constant problem. Modified oxochromium(VI)‐amine reagents on polymer supports have been prepared and examined with the objective of providing a regenerable reagent system which is serviceable on a practical scale. A significant improvement in routine oxidations utilizing PCC and PDC entails the addition of adsorbents such as Celite®, alumina, silica gel, molecular sieves, or zeolites. The distinct advantages associated with the use of adsorbents in oxochromium(VI)‐amine‐mediated oxidations are discussed. The importance of buffers and desiccants in oxochromium(VI) oxidations is discussed. Virtually any number of oxochromium(VI)‐amine reagents may be prepared by varying the amine ligand and/or acid species associated with oxochromium(VI), and many of these compounds have been tested using simple substrate alcohols for oxidation to carbonyl compounds. The search for a milder and more efficient oxidant than the Sarrett‐type oxochromium(VI) reagent systems as well as the nonchromium oxidants based on dimethyl sulfoxide or dimethyl sulfide led to an examination of the utility of pyridinium chlorochromate (PCC) in selective oxidations of alcohols. PCC was superior in terms of ease of preparation, shelf stability and economy. Since the introduction of PCC in 1975 the reagent has become a commercially available “textbook” compound and is usually the reagent of choice for routine large and small scale oxidations of alcohols to carbonyl compounds. Unlike the oxochromium(VI)‐pyridine adducts, PCC is an acid salt, and its properties have proven advantageous in a number of tandem oxidative reactions such as oxidative transpositions and oxidative cationic cyclizations. Several reviews address the versatility of PCC and its extension to many different types of oxidative conversions in single and multistep organic syntheses. While PCC was gaining widespread use, the utility of pyridinium dichromate (PDC) in solvents such as dimethylformamide (DMF) and dichloromethane was reported. PDC/DMF was useful for oxidizing allylic alcohols to the corresponding, α,β‐unsaturated carbonyl compounds and non‐conjugated aldehydes and primary alcohols to the corresponding carboxylic acids. The utilization of beyond the simple oxidation of alcohols, and it is now employed for various transformations. Many other types of substituted pyridines, nitrogen heterocycles and amines form chromates, dichromates, and chlorochromates which allow many different types of oxidative processes for a wide range of substrate molecules. This chapter surveys the many applications of oxochromium(VI) complexes in oxidative conversions of alcohols to carbonyl compounds. Alternative reagent systems based on modifications involving ligands, buffering agents, or adsorbents, as well as nonchromium(VI) oxidants are discussed. A variety of substrates have been included in the Tables so as to guide the synthetic chemist in selecting reagents and conditions that will be optimal for a given transformation. Oxidative conversions of alcohols through transpositions and cationic cyclizations giving carbonyl compounds as endproducts are included.

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Photochemical transformations of small ring compounds. 92. Intramolecular dipolar cycloaddition reactions with vinylbiphenyl-substituted 1,3-dipoles

Cited by 19 publications

References 21 publications

A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

The [3 + 2] Nitrone–Olefin Cycloaddition Reaction

The Oxidation of Alcohols by Modified Oxochromium( VI )–Amine Reagents

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