Neil Cockburn

Bio: Neil Cockburn is an academic researcher from University of Guelph. The author has contributed to research in topics: Bicyclic molecule & Cycloaddition. The author has an hindex of 5, co-authored 9 publications receiving 164 citations.

Ruthenium-catalyzed [2 + 2] cycloadditions of bicyclic alkenes with alkynyl phosphonates.

Abstract: Ruthenium-catalyzed [2 + 2] cycloadditions of bicyclic alkenes with alkynyl phosphonates were investigated. The phosphonate moieties were found to be compatible with the Ru-catalyzed cycloadditions giving the corresponding cyclobutene cycloadducts in low to excellent yield (up to 96%). Alkynyl phosphonates showed lower reactivity than other heteroatom-substituted alkynes such as alkynyl halides, ynamides, alkynyl sulfides, and alkynyl sulfones and required a higher reaction temperature and much longer reaction time.

Thieme Chemistry Journal Awardees -WhereAre They Now? Bicyclic Alkenes: From Cycloadditions tothe Discovery of New Reactions

Abstract: Recent work on synthetic applications of bicyclic al-kenesis reviewed, including synthesis of substituted bicyclic al-kenes,1,3-dipolar cycloadditions, ruthenium-catalyzed [2+2] cycloadditions,ruthenium-catalyzed cyclizations and isomerizations, rhodium-catalyzeddimerizations, ruthenium- and rhodium-catalyzed ring-opening reactions. 1 Introduction 2 Synthesis of Substituted Norbornadienes and Norbornenes 2.1 Synthesis of 2- and 2,3-Disubstituted Norbornadienes by DoubleLithium-Halide Exchange 2.2 Synthesis of Norbornadiene-2,3-diynes by Palladium-CatalyzedSonogashira Coupling Reactions 2.3 Synthesis of 2,3-Diarylnorbornadienes by Palladium-CatalyzedSuzuki Coupling Reactions 2.4 Synthesis of Substituted Bicyclic Alkenes by Iron-CatalyzedCoupling Reactions 3 1,3-Dipolar Cycloadditions of Bicyclic Alkenes 3.1 Intramolecular 1,3-Dipolar Cycloadditions of Norbornadiene-TetheredNitrile Oxides 3.2 Intramolecular 1,3-Dipolar Cycloadditions of Norbornadiene-TetheredNitrones 4 Ruthenium-Catalyzed [2+2] Cycloadditionsof Bicyclic Alkenes 4.1 Reactivity of the Alkene and the Alkyne Components 4.2 Heteroatom-Substituted Alkynes 4.3 Regioselectivities 4.4 Asymmetric Induction Studies 5 Ruthenium- and Rhodium-Catalyzed Reactions of HeterobicyclicAlkenes 5.1 Ruthenium-Catalyzed Cyclization Reactions of Oxabenzonorborneneswith Propargylic Alcohols 5.2 Ruthenium- and Rhodium-Catalyzed Isomerizations and Dimerizationsof Oxabenzonorbornenes 5.3 Ruthenium- and Rhodium-Catalyzed Ring-Opening Reactionsof 3-Aza-2-oxabicyclo[2.2.1]hept-5-enes 6 Conclusions

Ruthenium-Catalyzed Homo Diels–Alder [2 + 2 + 2] Cycloadditions of Alkynyl Phosphonates with Bicyclo[2.2.1]hepta-2,5-diene

Abstract: Ruthenium-catalyzed homo Diels–Alder [2 + 2 + 2] cycloadditions between alkynyl phosphonates and bicyclo[2.2.1]hepta-2,5-diene were studied. The observed reactivity was found to be dependent on the...

Ynamides: A Modern Functional Group For The New Millennium

Abstract: An Overview on Ynamines Alkynes represent one of the most important and versatile building blocks in organic synthesis. Heteroatom-substituted alkynes, which can be considered as subgroups of alkynes, have also been vastly utilized in developing synthetic methods. In particular, ynamines [1-amino-alkynes or N-alkynyl amines] became the most valuable subgroup of alkynes after the establishment of their practical synthesis in the 1960's. The first attempt at preparation of an ynamine was reported by Bode1,2 in 1892. While well-characterized ynamines were reported in 19583 and 1960,4 a practical synthesis was not achieved until the effort led by Viehe5 in 1963 in addition to other subsequent works. In the ensuing twenty years, the synthetic significance of ynamines in organic and organometallic chemistry was firmly established by the work of many creative synthetic chemists. These elegant pioneer works have been informatively and carefully reviewed by Viehe in 19676 and 1969;7 Ficini in 1976;8 Pitacco and Valentin9 in 1979; Collard-Motte and Janousek10 in 1986; Himbert11 in 1993; and most recently by us12,13 and Katritzky14. Open in a separate window The synthetic eminence of ynamines is well merited because of the predicable regioselectivity in their transformations as shown by the generalization in Scheme i, and more importantly, because they are inherently highly reactive. However, this latter attribute is also the source of the limitation that has seriously hampered the development of ynamine chemistry, thereby shortening the period of its prominence in synthesis. Ynamines are very sensitive toward hydrolysis, as protonation of the electron-rich alkynyl motif affords reactive keteniminium intermediates, which upon trapping with water leads to simple amides in a rather expensive manner (Scheme i). This hydrolytic instability has caused much difficulty in the experimental preparation and general handling of ynamines, and more detrimentally, rendered ynamine chemistry inaccessible. Open in a separate window Scheme i Consequently, the synthetic utility of ynamines has suffered a dramatic decline during the last thirty years.15 The most glaring limitations have been in the development of intramolecular and stereoselective reactions.7–14 The only reported intramolecular reaction of ynamines was Genet and Kahn's acid catalyzed addition of a hydroxyl group to an ynamine [i→ii in Scheme ii] in 1980,16 and although clever, it constitutes a hydrolytic process. Open in a separate window Scheme ii Besides Reinhoudt's17 sole account in 1987 reporting hetero-[4 + 2] cycloadditions of chiral ynamine iii with nitroalkenes that led to cycloadducts iv in modest de, the only other notable studies were reported ten years later by Fischer18 showcasing [2 + 2] cycloadditions of chiral ynamides v and vi with vinylidene chromium carbene complexes, and another three years later by Pericas19 in their Pauson-Khand cycloadditions using chiral ynamines vii.

Cycloadditions and cyclizations of acetylenic, allenic, and conjugated dienyl sulfones.

Abstract: 2.3.1. IMDA Reactions of Acetylenic Sulfones 4512 2.3.2. IMDA Reactions of Allenic Sulfones 4513 2.3.3. IMDA Reactions of Dienyl Sulfones 4513 3. 1,3-Dipolar Cycloadditions 4514 3.1. With Azides 4514 3.2. With Diazo Compounds 4515 3.3. With Nitrones 4516 3.4. With Nitrile Oxides 4519 3.5. With Mesoionic Compounds 4519 3.6. With Other 1,3-Dipoles 4519 4. [2 + 2] Cycloadditions 4520 4.1. With Alkenes and Dienes 4520 4.2. Intramolecular [2 + 2] Cycloadditions 4522 4.3. With Imines, Enamines, Ynamines, And Enol Ethers 4522 4.4. Other [2 + 2] Cycloadditions 4523 5. Miscellaneous Cycloadditions 4524 6. Ene Reactions 4524 7. Cyclizations of Bis(allenic) Sulfones and Their Congeners 4526