Lewis Acid-Promoted Mukaiyama Aldol-Prins (MAP) Cyclizations of Acetals, Ketals, α-Acetoxy Ethers, and Orthoformates.

The Mukaiyama aldol-Prins (MAP) cyclization of acetals stereoselectively provided substituted tetrahydropyrans. The scope of the reaction has been expanded to include other electrophiles, including ketals and α-acetoxy ethers. Finally, a double MAP cyclization with orthoformates is described.

Total synthesis of leucascandrolide a: a new application of the Mukaiyama aldol-Prins reaction.

A total synthesis of the marine natural product leucascandrolide A has been completed. The titanium tetrabromide-mediated Mukaiyama aldol-Prins (MAP) reaction with aldehydes developed in our group provided a highly convergent and stereoselective method for assembling the core of the molecule. A new class of MAP reactions with acetals is introduced, and mechanistic considerations for both MAP methods are described. The total synthesis was completed by coupling of the side chain through two avenues: a known Still-Gennari olefination and a new Z-selective aldol/dehydroselenation reaction. Both procedures were highly selective and provided the natural product.

Electron-poor benzonitriles as labile, stabilizing ligands in asymmetric catalysis.

[structure: see text] A chiral palladium catalyst [(S)-MeObiphep)Pd(NCAr)2(SbF6)2, (S)-4c], has been developed for a variety of asymmetric transformations. (S)-4c is bench-stable and has activity comparable to that of the nitrile free Lewis acid catalyst for Diels-Alder, hetero-Diels-Alder, and glyoxylate-ene reactions.