Insofar as one of the fundamental objectives of organic synthesis is the construction of complex molecules from simpler ones, the importance of synthetic efficiency becomes immediately apparent and has been well-recognized.1 The increase in molecular complexity2 that necessarily accompanies the course of a synthesis provides a guide (and a measure) of synthetic efficiency. As a goal, one would like to optimally match the change in molecular complexity at each step with reactions of comparable synthetic complexity. Thus, the creation of many bonds, rings, and stereocenters in a single transformation is a necessary (though not sufficient) condition for high synthetic efficiency. The ultimate, perfect match would constitute single-step syntheses. More realistically, especially in view of the desire for general synthetic methods, the combination of mulScott E. Denmark was born in New York in 1953. He obtained an S.B. degree from MIT in 1975 and carried out research with Daniel Kemp and Richard Holm. His graduate studies at the ETH-Zurich with Albert Eschenmoser culminated with the D. Sc. Tech. degree in 1980. That same year he joined the faculty of the University of Illinois at UrbanasChampaign and was promoted to full professor in 1987. In 1991 he was named the Reynold C. Fuson Professor of Chemistry. His research interests are primarily in the invention of new synthetic reactions, structure and reactivity of organoelement reagents, and the origin of stereocontrol in fundamental carbon−carbon bond forming reactions.

Tandem [4+2]/[3+2] Cycloadditions of Nitroalkenes.

Cyclizations of N-acyliminium ions.

Palladium-catalyzed cycloisomerizations of enynes and related reactions

Over the past decade, large strides have been achieved in the invention of methods for the direct enantioselective addition of alkynes and metal alkynylide nucleophiles into prochiral aldehydes, ketones, and imines. This review highlights and compares the available methods for these transformations.

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The Enantioselective Addition of Alkyne Nucleophiles to Carbonyl Groups

Chiral heterocycles by iminium ion cyclization.

Aus dem Aldehyd (Ia) erhalt man mit Lithium-bis-trimethylsilylamid (IV) das N-Trimethylsilylimin (Ib), das mit Allylgrignard-Verbindungen umgesetzt und zum allylierten Amin (II) in hoher Ausbeute verseift wird.

Preparation of primary amines and 2-azetidinones via N-(trimethylsilyl)imines

N-Trimethylsilyl imines: applications to the synthesis of β-lactams

Rearrangements d'alcenyl-1 oxo-5 pyrroline-1iums et d'alcenyl-1 oxo-6 tetrahydro-3,4,5,6 pyridiniums (formes a partir des alcene-3yl-1 hydroxy-5 pyrrolidones-2 et -hydroxy-6 piperidones-2) en indolizidones-3, pyrrolizidones-3 et quinolizidones-3. Application a la synthese de l'hastanecine et de l'heliotridine

Teng Kuei Yang

Papers

Preparation of primary amines and 2-azetidinones via N-(trimethylsilyl)imines

N-Trimethylsilyl imines: applications to the synthesis of β-lactams

N-Acyliminium ion rearrangements: generalities and application to the synthesis of pyrrolizidine alkaloids