Dehydrogenation and Cyclization Reactions in Carotene Biosynthesis

1989 ◽  
pp. 287-292
Author(s):  
P. Beyer ◽  
H. Kleinig
Keyword(s):  
Cyclization Reactions

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

scholarly journals Pt(II)-Decorated Covalent Organic Framework for Photocatalytic Difluoroalkylation and Oxidative Cyclization Reactions

2021 ◽  
Vol 13 (5) ◽  
pp. 6349-6358
Author(s):  
Zainab Almansaf ◽  
Jiyun Hu ◽  
Federica Zanca ◽  
Hamid R. Shahsavari ◽  
Benjamin Kampmeyer ◽  
...  
Keyword(s):  
Oxidative Cyclization ◽  
Cyclization Reactions ◽  
Covalent Organic Framework ◽  
Organic Framework

scholarly journals Oxidative cyclo-rearrangement of helicenes into chiral nanographenes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chengshuo Shen ◽  
Guoli Zhang ◽  
Yongle Ding ◽  
Na Yang ◽  
Fuwei Gan ◽  
...  
Keyword(s):  
Functional Materials ◽  
Optical Devices ◽  
Oxidative Cyclization ◽  
Synthetic Chemistry ◽  
Aromatic Rings ◽  
Cyclization Reactions ◽  
Rearrangement Reaction ◽  
Skeletal Reconstruction ◽  
Gradual Release

AbstractNanographenes are emerging as a distinctive class of functional materials for electronic and optical devices. It is of remarkable significance to enrich the precise synthetic chemistry for these molecules. Herein, we develop a facile strategy to recompose helicenes into chiral nanographenes through a unique oxidative cyclo-rearrangement reaction. Helicenes with 7~9 ortho-fused aromatic rings are firstly oxidized and cyclized, and subsequently rearranged into nanographenes with an unsymmetrical helicoid shape through sequential 1,2-migrations. Such skeletal reconstruction is virtually driven by the gradual release of the strain of the highly distorted helicene skeleton. Importantly, the chirality of the helicene precursor can be integrally inherited by the resulting nanographene. Thus, a series of chiral nanographenes are prepared from a variety of carbohelicenes and heterohelicenes. Moreover, such cyclo-rearrangement reaction can be sequentially or simultaneously associated with conventional oxidative cyclization reactions to ulteriorly enrich the geometry diversity of nanographenes, aiming at innovative properties.

scholarly journals Activation modes in biocatalytic radical cyclization reactions

2021 ◽  
Author(s):  
Yuxuan Ye ◽  
Haigen Fu ◽  
Todd K Hyster
Keyword(s):  
Heme Iron ◽  
Radical Cyclization ◽  
Cytochrome P450 Monooxygenases ◽  
Radical Cyclizations ◽  
Cyclization Reactions ◽  
Complex Molecules ◽  
P450 Monooxygenases ◽  
Non Heme Iron ◽  
Essential Reactions ◽  
Isopenicillin N

Abstract Radical cyclizations are essential reactions in the biosynthesis of secondary metabolites and the chemical synthesis of societally valuable molecules. In this review, we highlight the general mechanisms utilized in biocatalytic radical cyclizations. We specifically highlight cytochrome P450 monooxygenases (P450s) involved in the biosynthesis of mycocyclosin and vancomycin, non-heme iron- and α-ketoglutarate-dependent dioxygenases (Fe/αKGDs) used in the biosynthesis of kainic acid, scopolamine, and isopenicillin N, and radical S-adenosylmethionine (SAM) enzymes that facilitate the biosynthesis of oxetanocin A, menaquinone, and F420. Beyond natural mechanisms, we also examine repurposed flavin-dependent ‘ene’-reductases (ERED) for non-natural radical cyclization. Overall, these general mechanisms underscore the opportunity for enzymes to augment and enhance the synthesis of complex molecules using radical mechanisms.

ChemInform Abstract: Acid- and Enzyme-Catalyzed Cyclization Reactions of (Z,E)-1(10),4- Cyclodecadiene Derivatives as Model Systems for Melampolides.

ChemInform ◽  
2010 ◽  
Vol 28 (51) ◽  
pp. no-no
Author(s):  
D. P. PIET ◽  
H. M. WILLEMEN ◽  
T. J. M. DE BRUIN ◽  
M. C. R. FRANSSEN ◽  
J. B. P. A. WIJNBERG ◽  
...  
Keyword(s):  
Model Systems ◽  
Cyclization Reactions
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