l-Proline catalyzed direct diastereoselective aldol reactions: towards the synthesis of lyxo-(2S,3S,4S)-phytosphingosine

Rapid Synthesis of the epi-Biotin Sulfone via Tandem S,N-Carbonyl Migration/aza-Michael/Spirocyclization and Haller-Bauer Reaction

A synthesis of 2-epi-biotin sulfone was accomplished from commercially available l-cysteine. The synthesis features an unprecedented tandem S,N-carbonyl migration/aza-Michael/spirocyclization reaction from an l-cysteine-derived enone with aq. ammonia, in which three new sigma bonds and two rings are formed. In addition, the synthesis includes a highly diastereoselective late-stage Haller-Bauer reaction of sulfone for direct introduction of the carbon side chain.

Stereoselective Synthesis of β-Amino Ynones by the Addition of Alkynones to Nonracemic Sulfinimines: Formal Total Synthesis of l-Xylo and l-Arabino Phytosphingosines

The addition of silyl enol ethers obtained from ynones to sulfinimines furnished the corresponding β-sulfinamido ynones in a very good yield and diastereoselectivity. The formed ynones serve as precursors amenable for the synthesis of bioactive compounds. This has been illustrated in the synthesis of l-xylo and l-arabino phytosphingosines.

Enantioselective synthesis of Garner's aldehyde by asymmetric hydroformylation

Both enantiomers of Garner's aldehyde (3) are prepared from the same alkene 4 by catalytic asymmetric hydroformylation.

A facile synthesis of D-ribo-C(20)-phytosphingosine and its C2 epimer from D-ribose

A facile synthetic route to d-ribo-C(20)-phytosphingosine 31 and its C2 epimer 32 is described. The Overman rearrangement of allylic trichloroacetimidates derived from the known ribose derivative 7 has been used as the key step. The subsequent functional group interconversions in rearranged products 14 and 15 followed by Wittig olefination, Pd/C-mediated reduction and the removal of protecting groups successfully constructed the final molecules.

Enamine catalysis

The reversible reaction of primary or secondary amines with enolizable aldehydes or ketones affords nucleophilic intermediates, enamines. With chiral amines, catalytic enantioselective reactions via enamine intermediates become possible. In this review, structure-activity relationships and the scope as well as current limitations of enamine catalysis are discussed.