Lewis acid-promoted cascade reactions of cyclopropenes: a unified approach to stereoselective synthesis of cyclic ethers and oxaspirolactones.

Lewis acid-promoted 5/6- hydroalkoxylation/reduction cascade of ω-hydroxy cyclopropenes gave expeditious, stereoselective access to THF/THP derivatives. Monoester substituted ω-hydroxy cyclopropenes on treatment with catalytic Bi(OTf) lead to [5,5]/[6,5] oxaspirocyclic lactones. This unified strategy relies on generation of transient donor-acceptor (D-A) cyclopropanes from ω-hydroxy cyclopropene precursors.

Total Synthesis of Pyrrolidine and Piperidine Natural Products via TMSOTf-Mediated "5/6-" Reductive Hydroamination of Enynyl Amines.

Stereoselective syntheses of pyrrolidines and piperidines bearing hydrophobic chains have been achieved through a metal free, Lewis acid-mediated 5/6- reductive hydroamination cascade of enynyl amines. The brevity of the developed strategy allowed for the collective stereoselective total synthesis of various alkaloids, including (±)-pyrrolidine -225H, (±)--197B, (±)--225C, the family of (+)-solenopsins and (+)-isosolenopsins, and the formal synthesis of (±)-bgugaine and (+)-azimic acid.

Cu(II)/PTABS-Promoted, Regioselective SAr Amination of Polychlorinated Pyrimidines with Mechanistic Understanding.

Regioselective amination of polyhalogenated heteroarenes (especially pyrimidines) has extensive synthetic and commercial relevance for drug synthesis applications but is plagued by the lack of effective synthetic strategies. Herein, we report the Cu(II)/PTABS-promoted highly regioselective nucleophilic aromatic substitution (SAr) of polychlorinated pyrimidines assisted by DFT predictions of the bond dissociation energies of different C-Cl bonds. The unique reactivity of Cu(II)-PTABS has been attributed to the coordination/activation mechanism that has been known to operate in these reactions, but further insights into the catalytic species have also been provided.

Heavy and less common metals in rainwater and the kinetics of the oxidation of hydrogen sulfide by oxygen in rainwater medium.

As a sequel to our recent study on the oxidation by O, i. e., autoxidation of dissolved hydrogen sulfide, HS, in aqueous medium, we present here the results of a similar study in rain water medium.

Transposition of an acrylate moiety in TMSOTf-mediated reaction of alkynyl vinylogous carbonates gives heterocyclic dienes.

TMSOTf-mediated reaction of alkynyl vinylogous carbonates serendipitously gave 1,4-oxazepine and dihydropyran dienes transposition of an ethyl acrylate moiety involving intramolecular cascade Prins-type cyclization/retro-oxa-Michael reaction/cycloisomerisation. The developed atom-economical protocol selectively provides an double bond geometry. Dihydropyran dienes could be reduced diastereoselectively using EtSiH/TMSOTf or could be transformed into polycyclic heterocycles by Heck reaction.