Synthesis of Bridged Heterocycles via Sequential 1,4- and 1,2-Addition Reactions to α,β-Unsaturated N-Acyliminium Ions: Mechanistic and Computational Studies

Synthesis of cyclic aza-peroxides (microreview)

A summary of approaches developed for the synthesis of stable cyclic aza-peroxides is presented.

TMSOTf-mediated synthesis of skipped dienes through the addition of olefins to imines and semicyclic N,O-acetals

A novel approach to skipped dienes has been developed through the TMSOTf-mediated one-pot addition-substitution of olefins 2a, 2f and 2g with imines 1a-1g, and a series of aryl substituted skipped dienes 3aa-3gf were accordingly obtained in 62%-94% yields. Moreover, semicyclic N,O-acetals 5 and 7 could also undergo this transformation to produce the corresponding skipped dienes 6aa and 6af-6al and 8ba and 8bf-8bk in moderate to good yields.

Characterization and Utilization of the Elusive α,β-Unsaturated N-Tosyliminium: the Synthesis of Highly Functionalizable Skipped Halo Enynes

A formal haloalkynylation of allenamides has been described for the synthesis of highly stereo- and regioselective skipped halo enynes. Exclusive γ-regioselectivity is achieved through the intermediacy of a conjugated N-tosyliminium intermediate-direct evidence for the formation of which was validated by NMR and HRMS. Quantum mechanical computations reveal that the reactive intermediate geometry is key to controlling the 1,2- or 1,4-regioselectivity of alkyne interception. Divergent access to elusive unsaturated systems has also been reported.

Synthesis of spirocyclic heterocycles from α,β-unsaturated N-acyliminium ions

The reactions of α,β-unsaturated N-acyliminium ions, generated in situ from 4(S)-O-substitutedhydroxy-5-hydroxy-5-vinyl-N-alkylpyrrolidin-2-ones, with allylsilanes and indoles leading to the formation of spirocyclic heterocycles, are reported.

1,2-Addition versus homoconjugate addition reactions of indoles and electron-rich arenes to α-cyclopropyl N-acyliminium ions: synthetic and computational studies

α-Cyclopropyl-N-acyliminium ions towards reaction with indoles to give 5-(3-indoyl)-5-cyclopropylpyrrolidin-2-ones and, in the case of highly electron deficient indoles and electron rich arenes, spiroheterocycles.

Preparation of pyrrolizinone derivatives via sequential transformations of cyclic allyl imides: synthesis of quinolactacide and marinamide

A facile synthetic route toward the preparation of pyrrolizinone derivatives has been developed and applied for the synthesis of quinolactacide/marinamide.

Cyclic Enecarbamates as Precursors of α,β-Unsaturated Iminium Ions: Reactivity and Synthesis of 6,6-Spirocyclic Ring Systems

The scalable synthesis of cyclic enecarbamates and their use as convenient precursors of α,β-unsaturated N-acyl iminium ions is reported. The newly developed route overcomes synthetic and reactivity difficulties in previously reported methods, is readily scaled up, and proceeds through stable intermediates suitable for long-term storage if required. Preliminary investigations probing the reactivity of cyclic α,β-unsaturated N-acyl iminium ions as dienophiles in Diels-Alder reactions and electrophilic alkylating agents are described. In the presence of Lewis and Brønsted acids, iminium precursor 22a underwent efficient Diels-Alder cycloaddition with a range of simple and complex dienes, culminating in the synthesis of 6,6-spirocyclic ring systems possessing the same relative stereochemistry as the spirocyclic imine present in the marine natural product gymnodimine 1.