137732-39-9Relevant articles and documents
Late-Stage C-H Alkylation of Heterocycles and 1,4-Quinones via Oxidative Homolysis of 1,4-Dihydropyridines
Gutiérrez-Bonet, álvaro,Remeur, Camille,Matsui, Jennifer K.,Molander, Gary A.
supporting information, p. 12251 - 12258 (2017/09/12)
Under oxidative conditions, 1,4-dihydropyridines (DHPs) undergo a homolytic cleavage, forming exclusively a Csp3-centered radical that can engage in the C-H alkylation of heterocyclic bases and 1,4-quinones. DHPs are readily prepared from aldehydes, and considering that aldehydes normally require harsh reaction conditions to take part in such transformations, with mixtures of alkylated and acylated products often being obtained, this net decarbonylative alkylation approach becomes particularly useful. The present method takes place under mild reaction conditions and requires only persulfate as a stoichiometric oxidant, making the procedure suitable for the late-stage C-H alkylation of complex molecules. Notably, structurally complex pharmaceutical agents could be functionalized or prepared with this protocol, such as the antimalarial Atovaquone and antitheilerial Parvaquone, thus evidencing its applicability. Mechanistic studies revealed a likely radical chain process via the formation of a dearomatized intermediate, providing a deeper understanding of the factors governing the reactivity of these radical forebears.
NOVEL METHOD FOR PREPARATION OF ATOVAQUONE
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Page/Page column 35-36, (2012/12/13)
Provided is a process of preparation of 2-[trans,-4-(4'-chlorophenyl)cyclohexyl]-3-hydroxy- 1,4-naphthoquinone, i.e. Atovaquone [I] which is cost effective, green, and eco-friendly process, without separation of any diastereomers or geometric isomers of intermediates obtained during the reactions. Also provided is separation of 'cis' and 'trans ' isomer of intermediates VI, VII and VIII through selective crystallization in an appropriate solvent. A method for converting 2-[cis,-4-(4'-chlorophenyl)cyclohexyl]-3-hydroxy-1,4-naphthoquinone to 2-[trans-4-(4'-chlorophenyl)cyclohexyl]-3-hydroxy-l,4-naphthoquinone in presence of Lewis/ Bronsted acid is also provided. A process for preparation of compound 2-(4-(4- chlorophenyl)- 1 -hydroxy cyclohexyl)-3,4-dihydronaphthalen- 1 (2H)-one [IV] comprising condensation of (1,2-dihydronaphthalen-4-yloxy)trimethylsilane [II] with 4-(4- chlorophenyl)cyclohexanone [III] in presence of Lewis acid in organic solvent. The invention also encompasses a highly efficient and atomeconomic process for synthesis of compound [III] i.e. 4-(4-chlorophenyl)cyclohexanone as well as a process for synthesis of 2-[cis-4-(4'- chlorophenyl)cyclohexyl]-3-hydroxy-l,4-naphthoquinone. Further provided is a process for isomerization of cis- Atovaquone i.e. 2-[cis-4-(4'-chlorophenyl)cyclohexyl]-3-hydroxy-l,4- naphthoquinone to tnms-Atovaquone i.e. 2-[trans-4-(4'-chlorophenyl)cyclohexyl]-3- hydroxy- 1,4-naphthoquinone in presence of Lewis acid.