Z. Valenta

Quassin and Neoquassin

Abstract Structure XIX (R1 = H; R2 = CH3) was derived for quassin on the basis of extensive chemical and physical evidence.

The stereochemistry of quassin

Abstract The relative configuration of quassin and several of its derivatives has been derived.

A Synthetic Approach to Quassin. Introduction of Functionality and Stereochemistry by a Diels–Alder Reaction

Using a Lewis acid catalyzed Diels–Alder reaction as the key step, the crystalline synthetic intermediate (17) has been prepared. Compound 17 contains all C-atoms of quassin (1) and stereochemistry and 0-functionality suitable for the conversion into 1.

The total synthesis of optically active veatchine.

Die erste Totalsynthese des Garrya-Alkaloids Veatchin, das heisst des natürlichen optischen Isomeren, wird beschrieben.

An Asymmetric Total Synthesis of D-Homo Steroids Involving a Lewis Acid Directed Diels-Alder Reaction

Abstract In recent years, applications of asymmetric, amino acid mediated aldol cyclizations1,2 have led to major advances in steroid total synthesis.3 Typical of such processes is the conversion of prochiral triketone la 4 to the steroid CD-synthon, (S)-(+)-enedione 2a in high chemical and optical yield, under the influence of (S)- proline.1,2 This approach to the introduction of chirality is the foundation upon which several enantiospecific and highly efficient syntheses of biologically important steroids (19-norsteroids, A-ring aromatic steroids, androstanes) or their precursors are based.3

On the structure of ryanodol.

Anhydroryanodol besitzt eine den Strukturen I, II oder III entsprechende Laktonformel. Die Struktur des Ryanodols ist in der allgemeinen Formulierung XVII-XIX enthalten. Das Problem der Ryanodolbiogenese wird kurz diskutiert.

The complete structure of ryanodine.

Die Struktur des Ryanodins und die Natur der Ryanodin-Anhydroryanodin-Umlagerung wird diskutiert.

The complete structure and relative and absolute configuration of anhydroryanodine

Für Anhydroryanodin wurde Struktur IV bewiesen.

NEIGHBOURING GROUP DIRECTED PROTONATION IN THE BIRCH REDUCTION OF STYRENE DOUBLE BONDS

Abstract A neighbouring hydroxyl group mediates a diastereoselective protonation in the Birch reduction of styrene double bonds.