polysubstituted cyclobutanones by [2 + 2]-cycloaddition of ketenes with chiral acyclic enol ethers is reported. A wide variety of easily accessible di- and monosubstituted ketenes were found to react with a very high degree of stereoselectivity with chiral, Stericol derived, acyclic enol ethers. This combination of simple reagents provides straightforward entry to highly substituted enantioenriched
Silicon-containing amides, e.g., N-[1'-phenyl-2'-(4"-methylphenyl)ethyl]-2,2,6,6-tetramethyl-1-oxa-2,6-disi lacyclohexane-4-carboxamide, are useful as anti-atherosclerotic agents. The amides are obtainable by acylation of a primary amine (the substituents on the amine being of the aralkyl phenyl, tryptophanyl, benzocycloalkyl-type) with a corresponding silicon-containing carboxylic acid (or active form thereof).
The totalsynthesis of (−)-omuralide, a potent specific proteasome inhibitor, has been achieved through an unprecedented route. The C3 and C4 chiral centers of the natural product have been selectively installed by an asymmetric [2 + 2]-cycloaddition between an unusual oxadisilinane ketene and a chiral enol ether, while the γ-lactam core was prepared by a single-pot two-step Beckmann transposition