Large Ring Systems Research Articles

2 + 2]‐Cycloreversions

AbstractFour‐membered rings can be cleaved thermally, Photochemically, or catalytically into two π bonded fragments. Theoretical calculations, kinetic studies, and investigations of stereo‐ and regioselectivity have been undertaken to clarify the question of whether the reaction involves one or two steps and to permit predictions on its course. [2 + 2]‐Cycloreversions have been used to clarify the structure of four‐membered rings, to prepare highly reactive π electron‐systems and–in combination with a [2 + 2]‐cycloaddition–to protect double bonds. The combination of a cycloaddition and‐reversion can be used to convert a carbonyl group into an olefin. Starting with compounds containing annelated four‐membered rings, compounds with two functional groups or large ring systems can be prepared. [2 + 2]‐Cycloreversions have also been discussed in connection with storage of solar energy.

Synthesis and Reactions of 4‐Chromanones

AbstractMany natural products, such as the plant insecticides rotenone and ageratochromene (precocene), some fungitoxic phytoalexins, hashish constituents, vitamin E, and plant pigments, contain the chroman ring system as common structural unit. Some years ago we discovered a particularly simple entry to this class of heterocyclic compounds: The condensation of o‐hydroxyacetophenones with aliphatic aldehydes and ketones in the presence of pyrrolidine leads to 4‐chromanones in good yields. The scope of application and limitations as well as modification of this versatile synthesis are outlined; the accompanying tables give a good indication of the wealth and variety of possible substituents. The reaction of o‐hydroxyacetophenone, e. g. with glyoxylic acid or with α,β‐unsaturated ketones, proceeds atypically. The majority of the new chromanones can be used, inter alia, for the preparation of chromones, chromones and chromons, and for the synthesis of tricyclic and larger ring systems.

ChemInform Abstract: EIGHT‐MEMBERED AND LARGER RING SYSTEMS

Chemischer InformationsdienstVolume 12, Issue 43 Reviews ChemInform Abstract: EIGHT-MEMBERED AND LARGER RING SYSTEMS G. M. BROOKE, G. M. BROOKESearch for more papers by this author G. M. BROOKE, G. M. BROOKESearch for more papers by this author First published: October 27, 1981 https://doi.org/10.1002/chin.198143342AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume12, Issue43October 27, 1981 RelatedInformation

A ring expansion route to benzo substituted medium- and large-ring systems. Synthesis of trans-7,8-benzocyclododeca-5,7-dien-1-one

A ring expansion route to benzo substituted medium- and large-ring systems. Synthesis of trans-7,8-benzocyclododeca-5,7-dien-1-one

シクロファンの構造化学

Cyclophanes are the compounds in which more than two atoms of an aromatic ring are incorporated into a medium or large ring system. Cyclophanes have highly strained molecular structure with abnormal physical properties and chemical reactivities. Molecular structures of wide variety of para and metacyclophanes have been determined by X-ray diffraction since the discovery of (2.2) paracyclophane by Brown in 1949. Unusual physical properties investigated by NMR and UV spectra were interpreted in terms of strained molecular structure and transannular interaction of π-electrons of benzene rings. Experimental measurement and theoretical treatment using empirical valence-force potentials were made to estimate the strain energy of cyclophanes quantitatively.

The Synthesis of Some 9-,10-, and 11-Membered Ring Compounds Containing a Nitrogen Atom: 2,3,4,5,6,7-Hexahydro-1H-3-Benzazonines, 1,2,3,4,5,6,7,8-Octahydro-3-Benzazocines, and 2,3,4,5,6,7,8,9-Octahydro-1H-3-Benzazacy-cloundecanes

Abstract In previous papers the syntheses of seven-1 and eight-membered 2a, 2b ring compounds of the general formulas 5a, b have been described and the nine-membered2c homolog5c briefly mentioned. It was of interest to see whether the method of ring formation using an amino acid of type 3 was applicable to the preparation of larger ring systems. In this paper we would like to report the preparation of the bicyclic amines 5 which are the 9-, 10-, and 11-membered ring homologs of this series.

Electrochemical investigations of surface functional groups on isotropic pyrolytic carbon

Isotropie pyrolytic carbon (Pyrolite®) electrodes subjected to electrochemical oxidation at widely varying current densities develop a very distinctive, reproducible surface functionality. This surface functional group exhibits a peak reduction current in the region from 0 to–400 mV (vs. SCE) in 1 M H 2SO 4, and is easily quantitatively reduced. It can then be reoxidized, with a peak oxidation current occurring in the range from + 1300 to + 1700 mV (vs. SCE) in 1M H 2SO 4, to re-form the original surface group. The cycle can then be repeated ad infinitum, with quantitative reduction and oxidation every time. The oxidized and reduced forms of the surface functionality may correspond to quinone and hydroquinone groups. In view of the high dipole moment associated with quinone oxygen attached to large ring systems, a high electron density would be expected at the oxidized carbon surface. The specific adsorption of p-nitrophenol on carbon, thought to be an electron donor-acceptor complex, is shown to be strongly dependent on the state of surface oxidation. Coulometric studies indicate that the p-nitrophenol adsorption is favored on the oxidized surface.

Conformational studies of some normal, medium and large ring systems

Abstract