Paul Margaretha

Bio: Paul Margaretha is an academic researcher from University of Hamburg. The author has contributed to research in topics: Enone & Cycloaddition. The author has an hindex of 17, co-authored 308 publications receiving 1431 citations. Previous affiliations of Paul Margaretha include University of Geneva & Rockefeller University.

Furans from Novel [3 + 2] Photocycloaddition of Alkenes to 2-(1-Alkynyl)cyclohexenones

Abstract: Photocycloaddition of 2-alkynyl-substituted cyclohexenones (8c-11c) with isobutylene (2) and tetramethylethylene (3a) leads to tricyclic trans (15a-18a) and (15b-17b), respectively, in gas chromatographic yields of ∼90%. A suggested mechanism for this novel process is shown in eq 2. Tetramethoxyethylene (3b) gives only oxetanes (22) and (23), and the 3-methyl-substituted ketone (12c) fails to react with (2) and (3a,b). tert-Butylethylene gives [2+2] adduct (24) with (10c)

Novel 3 + 2 photocycloadditions of 3-(1-alkynyl)-2-cycloalken-1-ones with alkens

Abstract: Photochemical cycloaddition of 3-alkynylcycloalkenones with tetramethylethylene at ∼40 o C leads to mixtures of 1:1 adducts that arise largely from 1,5 closure of the biradical intermediate (eq 1), providing examples of a novel [3+2] cycloaddition reaction. Similar reactions occur between these same ketones and 1,1-dimethoxy-2-methylpropene and 1,1-dimethoxyethylene. This and previously observed temperature effects on related rearrangements of triplet biradicals suggest that such biradical rearrangements occur prior to and in competition with intersystem crossing to the singlet

Photoaddition Reactions of 5-Fluoro-4,4-dimethyl-2-cyclopentenone

Abstract: The photoaddition of 5-fluoro-4,4-dimethyl-2-cyclopentenone (4) to 2,3-dimethyl-2-butene leads specifically (in cyclohexane) and selectively (in acetonitrile) to the formation of the oxetanes 16. The title compound is compared in its behaviour to the analogous 6-fluoro-4,4-dimethyl-2-cyclohexenone (1) and both α'-fluoro-4,4-dimethyl-2-cycloalkenones in turn are compared to the corresponding 2-cycloalkenones (6 and 3) and 4,4-dimethyl-2-cycloalkenones (5 and 2). The quantum yield for the addition of these enones to 2,3-dimethyl-2-butene and to cyclopentene are discussed.

The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry†

Abstract: 3.7. Palladium Nanoparticles as Catalysts 888 3.8. Other Transition-Metal Complexes 888 3.9. Transition-Metal-Free Reactions 889 4. Applications 889 4.1. Alkynylation of Arenes 889 4.2. Alkynylation of Heterocycles 891 4.3. Synthesis of Enynes and Enediynes 894 4.4. Synthesis of Ynones 896 4.5. Synthesis of Carbocyclic Systems 897 4.6. Synthesis of Heterocyclic Systems 898 4.7. Synthesis of Natural Products 903 4.8. Synthesis of Electronic and Electrooptical Molecules 906

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2+2] Photocycloaddition Reactions

Abstract: The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Developments in the chemistry and band gap engineering of donor-acceptor substituted conjugated polymers

Abstract: This paper reviews the tools to manipulate and minimize the band gap of conjugated (co)polymers. The effects of minimization of the bond length alternation and of the incorporation of donor-π-acceptor units are discussed in particular. A systematic study of a series of alternating donor–acceptor oligomers has revealed the achievable limits and allowed for a prognosis of the performance of corresponding copolymers. The decisive influence of the LUMO eigenvectors of the acceptors on the band gap is highlighted. A new synthesis of benzo[1,2-c:4,5-c]bis[1,2,5]thiadiazole containing donor–acceptor monomers and their acid-catalyzed polymerization are described. Finally, band gap tuning by appropriate substitution, conformational adjustment and mesoscopic ordering is discussed.