I. Introduction 1485II. Scope of This Review 1485III. Transformations of Cyclobutane Derivatives inOrganic Syntheses1486A. Ring-Opening Reactions 1486B. Ring-Contraction Reactions 1493C. Ring-Expansion Reactions 14951. Five-Membered Rings 14952. Six-Membered Rings 15093. Seven-Membered Rings 15174. Eight-Membered Rings 15215. Nine-Membered Rings 1523IV. Transformations of Cyclobutane Derivatives inNatural Product Syntheses1524A. Ring-Opening Reactions 1524B. Ring-Expansion Reactions 15261. Five-Membered Rings 15262. Six-Membered Rings 15293. Seven-Membered Rings 15324. Eight-Membered Rings 1533V. Conclusion 1534VI. Acknowledgments 1534VII. References 1534

The application of cyclobutane derivatives in organic synthesis.

The use of arynes in organic synthesis

The diversity of mechanisms for enantiodiscrimination and of bond types that can be formed make Pd-catalyzed asymmetric allylic alkylation a powerful key step for simplification of synthetic strategy to complex molecular targets. Using a wide range of different classes of compounds including alkaloids, polyhydrofurans, nucleosides and carbanucleosides, cyclohexitols and cyclopentitols, chromanes, cyclopentanoids, amino acids, barbiturates, etc., novel synthetic strategies emerge that provide short efficient asymmetric syntheses.

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/joc-1994-69-5813%20trost%20review.pdf

Asymmetric allylic alkylation, an enabling methodology.

The Suzuki–Miyaura cross-coupling is a metal-catalysed reaction in which boron-based nucleophiles and halide-based electrophiles are reacted to form a single molecule. This is one of the most reliable tools in synthetic chemistry, and is extensively used in the synthesis of pharmaceuticals, agrochemicals and organic materials. Herein, we report a significant advance in the choice of electrophilic coupling partner in this reaction. With a user-friendly and inexpensive nickel catalyst, a range of phenyl esters of aromatic, heteroaromatic and aliphatic carboxylic acids react with boronic acids in a decarbonylative manner. Overall, phenyl ester moieties function as leaving groups. Theoretical calculations uncovered key mechanistic features of this unusual decarbonylative coupling. Since extraordinary numbers of ester-containing molecules are available both commercially and synthetically, this new ‘ester' cross-coupling should find significant use in synthetic chemistry as an alternative to the standard halide-based Suzuki–Miyaura coupling.

/pdf/decarbonylative-organoboron-cross-coupling-of-esters-by-5b8osmqg7y.pdf

Decarbonylative organoboron cross-coupling of esters by nickel catalysis

The total syntheses of polycyclic natural products by exploiting an aryne as the key reactive species are reviewed. A short introduction summarizes the basic reactivities of aryne species as well as the methods for its generation. In the main part, early examples and the recent reports (mainly 2012–present) on the use of arynes in multistep syntheses are described.

Aryne-based strategy in the total synthesis of naturally occurring polycyclic compounds.

A literature procedure for generating benzyne from 1-aminobenzotriazole and lead tetraacetate was modified by the use of two syringe pumps to effect simultaneous addition through opposing ports of a three-neck flask. Applied to the reaction of benzyne with 4-phenyloxazole at 0°C, this modification resulted in essentially quantitative formation of cycloadduct. Retro-Diels-Alder expulsion of benzonitrile with concurrent formation of isobenzofuran occurred when the adduct was heated. The sequence constitutes a useful method of preparation of isobenzofuran, which may be utilized in situ or isolated as a solution for subsequent application. Benzyne cycloadducts were also prepared from 4-(4-nitrophenyl)- and 4-(4-methoxyphenyl)oxazoles, in order to assess the effect of remote substituents on the retro-Diels-Alder reaction. First-order rate constants were determined at three temperatures in the range of 40-70°C. The order of reactivity was p-NO 2 >p-H>p-OMe; the substituent effects were small, with a factor <4 separating the p-NO 2 from p-OMe rate. Expulsion of the nitrile is believed to occur as a concerted reaction with little charge development

Benzyne-oxazole cycloadducts: isolation and retro-Diels-Alder reactions

General Enantiospecific Route to Isochromanquinones. Synthesis of (-)-Nanaomycin D

A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 9 upon sequential treatment with an organolithium reagent and then BF 3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5.Addition of an alkynyl-,alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl-4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9 and these readly rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene.In a similar fashion,15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones

Michael Winters

Papers

Benzyne-oxazole cycloadducts: isolation and retro-Diels-Alder reactions

General Enantiospecific Route to Isochromanquinones. Synthesis of (-)-Nanaomycin D

A potentially general regiospecific synthesis of substituted quinones from dimethyl squarate

A New Photoannulation Reaction of 2-Aryl-3-alkoxy-1,4-naphthquinones. Synthesis of Dimethylnaphthgeranine E

A New Photoannulation Reaction of 2‐Aryl‐3‐alkoxy‐1,4‐naphthoquinones. Synthesis of Dimethylnaphthgeranine E.