Showing papers on "Total synthesis published in 1982"

Tricyclo[3.3.0.02,8]octan‐3‐ones: Photochemically Prepared Building Blocks for Enantiospecific Total Syntheses of Cyclopentanoid Natural Products

Abstract: Bi- and tricyclopentanoid natural products have been in the focus of synthetic interest in recent years. With widely applicable building blocks lacking, most work has been restricted in the past to specific approaches to single racemic target structures. A novel concept is now presented which uses for the first time a simple building block, tricyclo[3.3.0.02,8]octan-3-one, providing enantiospecific access to diverse cyclopentanoid structures. Tricyclooctanone is obtained in a few steps and in high yield from benzene, via the triplet-sensitized oxadi-π-methane rearrangement of bicyclo[2.2.2]octenone as a photochemical key reaction. Smooth preparations of both enantiomers are possible by resolving the racemic mixture and of the bicyclooctenone. Owing to its structural properties the tricyclooctanone undergoes a wide array of regio- and stereoselective transformations in high yields, in compliance with the expectations for a synthetic key compound of general applicability. The total syntheses of boschnialactone, allodolicholactone, irido- and isoiridomyrmecin, and loganin aglucone 6-acetate provide the first examples of successful applications. Promising entries to coriolin, 6a-carbaprostacyclin and homologs, and 6,11-dehydroestrone complement this review of the potential of tricyclooctanone as a versatile building block for the enantiospecific total synthesis of polycyclopentanoids and related compounds.

Induction of Asymmetry by Amino Acids

Abstract: Since the stereoisomers of molecules with one or more asymmetric centers often exhibit different biological activities (e.g. thalidomide, pheromones), stereoselective synthesis as a method of preparative chemistry is rapidly attaining importance. Of the numerous drugs prepared by total synthesis that contain at least one asymmetric center, only about 20% have so far been used in sterically pure form. Amino acids constitute the greatest “chiral pool” of compounds whose enantiomers can be obtained commercially in large amounts; they are gradually being used more and more frequently as auxiliary agents or educts in asymmetric syntheses.

Necic acid synthons. Part 1. Total synthesis of integerrinecic acid

Abstract: The synthesis of racemic integerrinecic acid from ethyl acrylate is described. Overall, five steps are involved. A key synthon in the synthesis, ethyl (2Z)-2-bromomethylbut-2-enoate, can undergo either allylic substitution or substitution with rearrangement, and opens the way for a ‘general’ synthesis to a range of necic acids.

Total Synthesis and Electrophysiological Properties of Natural (−)‐Perhydrohistrionicotoxin, its Unnatural (+)‐Antipode and their 2‐Depentyl Analogs

Abstract: Natural (−)-perhydrohistrionicotoxin (6a), its unnatural (+)-antipode 6b, (−)-2-depentylperhydrohistrionicotoxin (7a) and its (+)-antipode 7b have been prepared and characterized. Kishi's lactam 8 reacted with optically active iso-cyanates, and the mixture of diastereomeric carbamates so obtained was separated and hydrolyzed yielding the optical antipodes of Kishi's lactam in optically pure form. Reduction with LiAlH4 yielded the optically active 2-depentyl analogs, while another sequence already developed in the racemic series afforded the natural toxin and its (+)-antipode. Some electrophysiological properties of these compounds are presented.