Amide-Group-Directed Protonolysis of Cyclopropane: An Approach to 2,2-Disubstituted Pyrrolidines

Electrochemical Formation of Oxazolines by 1,3-Oxyfluorination of Non-activated Cyclopropanes

The C-C bond in non-activated cyclopropanes can be intramolecularly cleaved with an electrochemically generated amidyl radical forming oxazolines. In the presence of TBABF4, this provides 1,3-oxyfluorination products. C-C bond cleavage of cyclopropane proceeds with inversion of the configuration, suggesting an intramolecular homolytic substitution (SHi) mechanism. The performance of TBABF4 as an efficient fluoride source was explained by accumulation of the BF4- anion at the anode surface, at which a carbocation is formed by the oxidation of the C-centered radical.

Scalable Synthesis of Biologically Relevant Spirocyclic Pyrrolidines

Synthetic approaches toward multigram preparation of spirocyclic α,α-disubstituted pyrrolidines from readily available starting materials are discussed. It was shown that although a number of synthetic methodologies have been known to date, many of the title compounds remain hardly accessible. The most appropriate literature method (which relied on reaction of imines and allyl magnesium halide, followed by bromocyclization) was identified and optimized. It was found that the method is most fruitful for simple non-functionalized substrates. Two novel approaches based on the Sakurai or Petasis reactions of cyclic ketones, followed by hydroboration-oxidation at the allyl moiety thus introduced, were elaborated. The latter method had the largest scope and was beneficial for the substrates containing organosulfur or protected amino functions. For the synthesis of 4-azaspiro[2.4]heptane, an alternative synthetic scheme commencing from tert-butyl cyclopropanecarboxylate (instead of the corresponding ketone) was developed. It was shown that the whole set of the methodologies developed can be used for the synthesis of various spirocyclic α,α-disubstituted pyrrolidines-advanced building blocks of potential importance to medicinal and agrochemistry-at up to a 100 g scale.

Synthesis of 2-acetyl trisubstituted furans via copper-mediated deacylation cleavage of unstrained C(sp3)–C(sp2) bonds

A copper-mediated tandem addition/cyclization/carbon–carbon cleavage reaction for the convenient synthesis of 2-acyl trisubstituted furans has been developed.