RESUMO
Biomass-derived 5-chloromethylfurfural (CMF), a congener of the well-known carbohydrate-based platform chemical 5-hydroxymethylfurfural (HMF), can efficiently be functionalised by radical transformations of its benzylic chloromethyl group. We report here the first examples of these radical reactions by way of metal-free, triethylborane/oxygen-induced atom transfer radical addition (ATRA) reactions between CMF and styrenes, which proceed with high yield and selectivity. The key intermediate, the 2-formyl-5-furfuryl radical derived from CMF, and its radical addition reactions were studied with regard to its electronic structure, i.e. spin density distribution and frontier molecular orbitals based on the NBO ansatz and activation barriers of the addition step using DFT and post-HF methods.
RESUMO
Tetrahydrocarbazoles and perhydrocyclohepta[b]indoles undergo a catalytic cascade singlet oxygenation in alkaline medium, which leads to chiral tricyclic perhydropyrido- and perhydroazepino[1,2-a]indoles in a single operation. These photooxygenation products are new synthetic equivalents of uncommon C,N-diacyliminium ions and can be functionalized with the aid of phosphoric acid organocatalysis.
RESUMO
The tricyclic azepino[1,2-a]indole acetates 7, readily accessible by visible-light-driven catalytic photooxygenation of cyclohepta[b]indoles 1, are convenient precursors to novel and uncommon cyclic C,N-diacyliminium ions 3. We report here the first Lewis acid-catalyzed C-C bond forming reactions of these species with TMSCN and silyl enol ethers as nucleophiles and utilizing TIPSOTf as well as Sc(OTf)3 as catalysts. Employing Sc(OTf)3/pybox complexes as a chiral catalyst system, regio- and enantioselective asymmetric alkylations with silyl enol ethers were achieved.