Some chemistry of chromenes and chromanones
type: CreativeWork
description: A range of 2-substituted, symmetrically and unsymmetrically 2,2- disubstituted and 2-spiro-annulated chroman-4-ones has been synthesised by the pyrrolidine catalysed condensation of 2-hydroxyacetophenones with aldehydes and ketones. The synthesis has been extended to yield 5-, 6, 7- and 8- substituted chromanones and the 5,6- and 7,8-benzologues. Additional chroman-4-ones have been prepared by the Fries rearrangement of aryl 3-methylbut-2-enoates. An n.m.r. analysis of chroman-4-ones has revealed that unsymmetrical substitution at C-2 leads to a preference for one conformer, whereas symmetrically substituted chromanones rapidly interchange between energetically equivalent conformers. Similar effects were observed with chroman-4-oximes, although some anomalous results were noted. Reduction and dehydration of the resulting chroman-4-ols yielded the corresponding chromenes. The established synthesis of chromenes involving the rearrangement of aryl propargyl ethers has been modified such that the chromene can be prepared directly by reaction of an alkynol with a suitably activated phenol at an alumina surface, without the need to prepare the intermediate ether. The addition of halogens and of hypobromous acid to chromenes has been examined. Increasing the size of the spiro-substituent at C-2 caused a change in the dihedral angle between 11-3 and 11-4 which was reflected in the n.m.r. spectra. Unsymmetrically 2-substituted chromenes yielded a diastereoisomeric mixture, the composition and configuration of which were dependent on the nature of the 2-substituents. The base catalysed dehydrobromination of 3-bromochroman-4-ols gave the 3,4-epoxychromans which were ring opened by lithium aluminium hydride and hydrogen chloride to yield the chroman-3-ols and their 4-chloro derivatives, respectively. Addition of water to the epoxides on activated alumina yielded the trans-chroman-3,4-diols; the isomeric &iadiols resulted from the permanganate oxidation of chromenes. The reactio…
abstract: A range of 2-substituted, symmetrically and unsymmetrically 2,2- disubstituted and 2-spiro-annulated chroman-4-ones has been synthesised by the pyrrolidine catalysed condensation of 2-hydroxyacetophenones with aldehydes and ketones. The synthesis has been extended to yield 5-, 6, 7- and 8- substituted chromanones and the 5,6- and 7,8-benzologues. Additional chroman-4-ones have been prepared by the Fries rearrangement of aryl 3-methylbut-2-enoates. An n.m.r. analysis of chroman-4-ones has revealed that unsymmetrical substitution at C-2 leads to a preference for one conformer, whereas symmetrically substituted chromanones rapidly interchange between energetically equivalent conformers. Similar effects were observed with chroman-4-oximes, although some anomalous results were noted. Reduction and dehydration of the resulting chroman-4-ols yielded the corresponding chromenes. The established synthesis of chromenes involving the rearrangement of aryl propargyl ethers has been modified such that the chromene can be prepared directly by reaction of an alkynol with a suitably activated phenol at an alumina surface, without the need to prepare the intermediate ether. The addition of halogens and of hypobromous acid to chromenes has been examined. Increasing the size of the spiro-substituent at C-2 caused a change in the dihedral angle between 11-3 and 11-4 which was reflected in the n.m.r. spectra. Unsymmetrically 2-substituted chromenes yielded a diastereoisomeric mixture, the composition and configuration of which were dependent on the nature of the 2-substituents. The base catalysed dehydrobromination of 3-bromochroman-4-ols gave the 3,4-epoxychromans which were ring opened by lithium aluminium hydride and hydrogen chloride to yield the chroman-3-ols and their 4-chloro derivatives, respectively. Addition of water to the epoxides on activated alumina yielded the trans-chroman-3,4-diols; the isomeric &iadiols resulted from the permanganate oxidation of chromenes. The reactio…
author: Brogden, Peter John
language: en
keywords: F100 - Chemistry
date published: 1986-11
date modified: 2026-07-24T01:36:13Z
provider: University of Central Lancashire
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Lancashire Polytechnic