Pierre Crabbé

Reduction of natural enones in the presence of cerium trichloride

The reduction of αβ-unsaturated ketones with sodium borohydride in methanol solution in the presence of cerium chloride gives almost exclusively the allylic alcohol, sometimes stereoselectively; the reduction of a variety of natural products containing a conjugated keto-group is described.

Observation on the synthesis of allenes by homologation of alk-1-ynes

An investigation is reported on the homologation of alk-1-ynes to allenes by the cuprous bromide-catalyzed reaction with formaldehyde and di-isopropylamine, including extension to an aromatic acetylene and a diacetylene. Optimization of yields was studied. A mechanism is proposed involving an intermediate hydrido-cuprate species derived from a 1:1 Mannich base–cuprous bromide π-complex. The mechanism is supported by labelling experiments and observed substituent effects.

Optical rotatory dispersion and circular dichroism or aromatic compounds: a general survey

Abstract A general survey of optical rotatory dispersion (ORD) and circular dichroism (CD) studies on aromatic compounds is given. Recent developments in equipment permit observation of Cotton effects associated with the α-band (ca. 260–280 mμ), and often of those associated with the p -band (ca. 220–240 mμ). The chromophores may be classified as (i) inherently dissymmetric or twisted chromophores (e.g. overcrowded polycyclic compounds, biaryls); (ii) coupled oscillators consisting of two non-conjugated aryl or related groups (e.g. calycanthine, lignans, benzyltetrahydroisoquinolines); (iii) single aryl chromophores perturbed by dissymmetric surroundings (e.g. oestrogenic steroids, indoles, mandelic acid derivatives, nucleosides). In classes (ii) and (iii) the rigid structures are dealt with before the flexible structures; since the geometry of the rigid structures is more precisely known, they can be better considered in theoretical terms. Many of the studies are of very piecemeal character, and it is hoped that this review will suggest areas where further work is likely to be most profitable. Applications of theory have been possible so far only within very limited fields.

Le diptérocarpol—II : Stéréochimie en C-13 et en C-17☆

Abstract Various reactions of ring D of dipterocarpol (hydroxy-dammarenone-II) show this triterpene to have the configuration 13β, 17αH, in accordance with biogenetic speculations.

Synthesis of homo-dinordrin, allenyl A-nor and dinor-steroids

Prompted by a recent Chinese report of the fertility inhibiting activity of Anordrin the preparation and biological evaluation of Dinordrin as the free alcohol and the corresponding diacetate and dipropionate were attempted and are reported in this summary of the chemical syntheses. The stereochemical configurations are pictured in the text along with the step-by-step synthesis routes.

Synthetic use of an unusual organocuprate intermediate

The organometallic intermediate (3) can be used to prepare iodo-allenes, and allenic and β-acetylenic ketones as well as ethers; the site of the reaction of an electrophile on the organometallic intermediate seems to depend on the hard or soft nature of the reagent according to Pearsons theory.

Synthesis of novel bicyclic prostaglandins by photochemical cycloaddition reactions

Light-induced addition reactions of cyclopentenone derivatives with ethylene, followed by elaboration of the alkyl chains at positions 8 and 12, give bicyclic prostanoic acid analogues belonging to the prostaglandin E2 and F2α series. Cycloaddition of ethylene to prostaglandin A2 methyl ester yields simultaneously the α- and β-cyclo-adducts. Photochemical addition of allene to prostaglandin A2 derivatives affords mixtures of photoadducts which vary with the nature of the functional group at position 15, thus illustrating the versatility of these photocondensation reactions.

Chemical synthesis and bioassay of anordrin and dinordrin I and II

The chemical synthesis of 2 alpha, 17 alpha-diethynyl-A-nor-5 alpha-androstane-2 beta, 17 beta-diol dipropionate (Anordrin) and the corresponding diacetate is reported. Similarly, the preparation of the 2 alpha, 17 alpha-diethynyl-A-nor-5 alpha-estrane-2 beta, 17 beta-diol, its diacetate and dipropionate (Dinordrin I), along with the corresponding 2 beta-epimer (Dinordrin II) from 17 beta-hydroxy-A-nor-5 alpha=estran-2-one is described. In rat uterotrophic activity bioassay, the slope of ethynylestradiol differed significantly from the slopes of the other three compounds, thus vitiating potency estimates with this reference compound. Dinordrin I was 20 times more potent than Anordrin and considerably more potent then Dinordrin II. The single-dose oral antifertility effect in rats generally paralleled uterotrophic activity. Immediate postovulatory contraceptive effectiveness was assessed in adult cycling female baboons given two doses daily for 4 days. Both Anordrin and Dinordrin I showed antifertility activity worthy of further study. Moreover, a definite luteolytic effect, with depression of both plasma estrogen and progesterone levels, was observed with these two steroids.

Etude comparative de la dispersion rotatoire optique et du dichroïsme circulaire en chimie organique

Abstract Optical rotatory dispersion and circular dichroism techniques are compared from the viewpoint of the organic chemist. Both methods are shown to present specific advantages and properties. For example, optical rotatory dispersion will be the method of choice for the study of the background effect and for optically active chromophores absorbing at low wave-lengths. Circular dichroism will be preferred when selectivity between two chromophores is sought, or for quantitative studies of the asymmetry around a chromophore. Also the detection of a weak Cotton effect or subtle conformational effects, masked by the background rotations of an optical rotatory dispersion curve, will be easier by circular dichroism.

Synthesis of ring modified prostaglandins

Abstract The total syntheses of the ring modified prostaglandins 8–12 , 16 , 18 , 20 , and 22 are described.