RESUMO
A new practical method has been developed for the α-heteroarylation of aliphatic nitriles with heteroarenes and azobis(alkylcarbonitriles) using Cu(OAc)2 as an oxidizing agent. This method allows the easy construction of nitrile-, aryl-, and dialkyl-bearing quaternary carbon centers from readily available building blocks, without requiring prefunctionalization steps. This reaction is based on adding cyanodialkyl radicals onto heteroarenes, including benzofurans, furans, pyrroles, and indoles. The resulting α-heteroaryl nitriles are useful synthetic intermediates and pharmacophores in biologically active molecules.
RESUMO
Pseudo-C2-symmetric dodecaheterocyclic structures, which possess two acyl/aroyl groups disposed on either a cis- or trans-relative configuration, were prepared from the naturally occurring (-)-(1R)-myrtenal. Addition of Grignard reagents (RMgX) to the diastereoisomeric mixture of these compounds unexpectedly showed that nucleophilic additions to the two prochiral carbonyl centers gave the same stereochemical result in both cis/trans diastereoisomers, making unnecessary the separation of this mixture. Noticeably, both carbonyl groups showed different reactivity because one of them is attached to an acetalic carbon and the other to a thioacetalic carbon. Furthermore, addition of RMgX to the carbonyl attached to the former carbon takes place through the re face, while addition to the second one proceeds through the si face, thus affording the corresponding carbinols in a highly diastereoselective process. This structural feature allowed the sequential hydrolysis of both carbinols, yielding separately (R)- and (S)-1,2-diols after reduction with NaBH4. The mechanism of the asymmetric Grignard addition was explained by density functional theory calculations. This approach contributes to the development of the divergent synthesis of structurally and/or configurationally different chiral molecules.
