Lewis acid-promoted Friedel-Crafts alkylation of alpha-ketophosphate electrophiles

I. Lewis Acid-Promoted Friedel-Crafts Alkylation of alpha-Ketophosphate Electrophiles: The alpha-alkylation of alpha-ketophosphate electrophiles by electron-rich neutral nucleophiles is described. The reaction is promoted by either BF3.OEt2 or ZnCl2. Aromatic, heteroaromatic, heteroatom and nonaromatic nucleophiles are tolerated. Electron-rich alpha-ketophosphates display the highest reactivity; electron-neutral and electron-poor substrates are also tolerated at elevated temperatures. Enantioenriched alpha-ketophosphate yields racemic product, lending evidence to an alpha-acyl carbenium ion intermediate. II. (3+2)-Annulation of Quaternary Donor-Acceptor Cyclopropanes and Aldehydes: The (3+2)-annulation of all-carbon donor site donor-acceptor cyclopropanes and aldehydes is described. Catalytic Sn(II), Sn(IV), or Hf(IV) facilitates the diastereoselective annulation. One-step access to highly substituted cis-tetrahydrofurans is possible. The reaction is tolerant of electron-rich and electron poor aromatic aldehydes, as well as alkenyl and aliphatic aldehydes. Mechanistic experiments with optically active cyclopropanes suggest an aldehyde nucleophilic substitution mechanism is operative and demonstrate that chirality transfer to the tetrahydrofuran products is possible. III. Enantioselective Synthesis of of Pyrrolidines From Racemic Cyclopropanes and Aldimines: Reaction Development and Mechanistic Insights A dynamic kinetic asymmetric (3+2)-annulation of racemic D-A cyclopropanes and N-benzyl aromatic aldimines is described. Enantio- and diastereoselective access to 2,5-cis pyrrolidines is possible through the use of a (4-Br-tBu-pybox)MgI2 catalyst. Results from experiments with cyclically-constrained (Z)-aldimine suggest that the major cis-isomer in the DyKAT is not a product of a (Z)-aldimine pathway