Carbocyclic Ring Systems Research Articles

Total Synthesis of (±)-Furodysin and (±)-Furodysinin

Abstract Furodysin and furodysinin, marine origin furanosesquiterpenes having a unique carbocyclic ring system, have been first synthesized as racemic forms from a cis-decalone derivative.

Claisen-rearrangement-mediated ring contraction of macrocyclic lactones : A new approach to carbocycles and heterocycles

Macrocyclic ketene acetals 3 undergo Claisen rearrangements smoothly and constitute a viable and general approach to hetero- or carbocyclic ring systems 4. This novel ring contraction process is subject to high internal asymmetric induction (cf. lactones 7 → carbocycles 8) as well as relative asymmetric induction in the rearrangements of ketene acetals derived from lactones 18, 23 and 27. Finally, N-benzoylmeroquinene methyl ester ( 37) was prepared to demonstrate the potential of this methodology in heterocycle synthesis.

Acetolysis of the trifluoromethanesulphonates of syn-12-hydroxyaldrin and syn-12-hydroxyisodrin and their dihydro derivatives : Reduction in neighbouring double bond participation effected by chlorine substituents

Acetolysis rates of the trifluoromethanesulphonates of two geometric isomers of hexachlorotetracyclo[6.2.1.1 3,6.O 2,7]dodeca-4,9-dien-12-ol ( 6, 8; syn-12-hydroxyaldrin, syn-12-hydroxy-isodrin) and of two geometric isomers of hexachlorotetracyclo[6.2.1.1 3,6.O 2,7dodec-9-en-12-ol ( 7, 9; syn-12-hydroxy-4, 5-dihydroaldrin, syn-12-hydroxy-4,5-hydroisodrin) have been determined. The results show that neighbouring double bond participation by a —ClCCCl— grouping that is juxtaposed to an incipient secondary carbenium ion (> CH·OSO 2CF 3 is negligible compared with that seen in the non-chlorinated prototypes containing an analogously-situated —CHCH— grouping (e.g. 4). The products of acctolysis of 8 and 9 were acetates of the original carbocyclic ring system, but the acctolysis of 6 at 64° yielded, as the sole rearranged product, a hexachloropentacyclo[7.2.1.O 2,8.O 3,5.O 4]dodecen-6-yl acetatc 10. The major products of acetolysis at 64° of 7 were a mixture of two isomeric hexachlorotetracyclol[6.3.1.O 2,9.O 3,7]dodecen-11-yl acetates( 17, 18) and a hexachloropentacyclo[6.4.0.O 2,10.O 3,7.O 9,11 dodec-4-ene 15; these were each formed via an initial bridging reaction and subsequent rearrangement steps. The factors that dictate the nature of products formed from each compound are discussed, and probable pathways to each are delineated.

Cäsium‐Effekt bei C–C‐Bindungsknüpfungen zu vielgliedrigen Kohlenwasserstoff‐Ringen

Cesium Effect in C–C‐Bond Forming Reactions Yielding Large Hydrocarbon RingsC–C‐bond formations of the Wurtz type following the Müller‐Röscheisen procedure [alkali metal + tetraphenylethene (TPE)] leading to [2n]paracyclophane rings 2 have been carried out, comparing sodium, potassium, and cesium as metals. As fig. 1 shows, the selectivity of the oligomer formation starting from 1,4‐bis(chloromethyl)benzene (1a) is strongly dependent on the alkali metal used. Sodium/TPE besides 2b predominantly yields the higher oligomers 2c – e. Use of cesium metal/TPE leads to 2b preferentially. With potassium metal/TPE all oligomers 2b – e are obtained in low yields or traces, respectively. According to these results, the oligomer formation in carbocyclic ring systems can be steered by the type of alkali metal applied; cesium seems to favour the formation of conformationally more rigid rings (like 2b).

Bicyclo[3.3.0]octenones in synthesis. An approach to the synthesis of the antitumor sesquiterpene quadrone

A synthetic approach to the antitumor sesquiterpene quadrone (1), based on intramolecular Michael reaction from a C-6 substituted bicyclo[3.3.0]oct-1 (2)-en-3-one [viz.(2)] is outlined. The preparations of the bicyclo-octenones (33b), (33a), and (41), precursors of (14), (15), and (16) respectively, are described, but attempts to induce these substrates [and the nitrone (42)]to undergo intramolecular Michael reactions to the carbocyclic ring system in quadrone, met with total failure.Treatment of the bromo ketone (58) with methanolic sodium methoxide resulted in smooth intramolecular alkylation producing the tricyclic dione (59) containing the carbocyclic ring system in quadrone (1).

Two diterpenes with new carbocyclic ring systems from an Australian collection of the brown alga Dictyota dichotoma

The dichloromethane extract of the brown alga Dictyota dichotoma has yielded a number of known diterpenes together with representatives of two previously unreported carbocyclic diterpene classes. The structure and absolute stereochemistry of the bicyclo[3,3,1]nonane derivative (6) was solved by single-crystal X-ray analysis of a heavy-atom derivative and the gross structure of the dialdehyde (8) was inferred from spectral evidence.

Taonianone, a new diterpene from the brown alga [formula omitted

Taonianone, a diterpene with a novel carbocyclic ring system has been isolated from the brown alga Taonia australasica .

Eine möglichkeit zur ringerweiterung des cyclooctins: synthese und reaktionen von 3,6-hexano-oxepin-4,5-dicarbonsäure-diethylester.

A reaction sequence for the cleavage of the triple bond of cyclooctyne to give various compounds with a carbocyclic ten-membered ring system is described.

Studies on marine natural products. I. 13-Membered carbocyclic cembranolide diterpenes from the soft coral Lobophytum pauciflorum (Ehrenberg).

Two cembranolide diterpenes were isolated from the Japanese soft coral Lobophytum pauciflorum (Ehrenberg). The structures of these diterpenes were identified as I and II, involving a 13-membered carbocyclic ring system unique in the soft coral literature.

Two sesquiterpene furans with new carbocyclic ring systems and related thiol acetates from a species of the sponge genus [formula omitted

Two sesquiterpene furans with new carbocyclic ring systems and related thiol acetates from a species of the sponge genus [formula omitted

Nuclear magnetic resonance spectroscopy. Carbon-carbon coupling in cyclopropane derivatives

The nature of the bonding in cyclopropane, the smallest and most highly strained carbocyclic ring system, has long been a lively and controversial topic. Walsh has described the carbon-carbon bonding in cyclopropane as involving a three-center bond, while Coulson and Moffitt and Trinajstic and have used quantum-mechanical treatments equivalent to bent bonds wherein the regions of highest electron density are not located along the C-C internuclear axes. Molecular orbital calculations of varying degrees of sophistication have been carried outs A recent summary of the description of bonding in cyclopropanes was given by Bernett.

The NMR spectra of four-membered carbocyclic ring systems

A summary of proton-proton coupling constant data for cyclobutanes, cyclobutanones, cyclobutenes and cyclobutenones is presented. In cyclobutanes, vicinal cis and trans coupling constants vary widely (4·6–11·5 c/s and 2·0–10·7 c/s, respectively), whereas the range of geminal coupling constants is smaller (−10·9 to −14·4 c/s. in the absence of a π-contribution). If the cyclobutane ring is incorporated into the strained bicyclo[2.1.1]-hexane system, then the geminal coupling constant is much smaller (−5·4 to −8·4 c/s) and a characteristic, large (6·7–8·1 c/s) 4σ-bond coupling between endo protons of the cyclobutane ring is observed. The vinylic coupling constant in cyclobutenes varies from 2·5–4·0 c/s (perhaps negative in sign) and the vicinal coupling between protons attached to adjacent sp2 and sp3 carbon atoms is very small (∼0–1 c/s). Values of J13CH are tabulated. Chemical shift data indicate that protons in cyclobutanes and cyclobutenes resonate at slightly lower field than those in the larger cycloalkanes and cycloalkenes.

Terpenoids—L : Transformation products of costunolide

Costunolide, containing a ten-membered carbocyclic ring system with the unique distribution of double bonds, undergoes many interesting transformations. The diol prepared by lithium aluminium hydride reduction of costunolide when subjected to metal amine reduction gives a hydrocarbon, C 15H 26, a secondary alcohol, C 15H 26O, and a primary alcohol, C 15H 26O, and a primary alcohol, C 15H 26O to which structures, VIII, X and XII have been assigned on the basis of spectral data and their conversions to elemene-type products on pyrolysis and to mono-ethenoid bicyclic products on acid catalysed cyclization. The secondary alcohol X has been converted to d-junenol which constitutes a new synthesis of the alcohol from costunolide. Pyrolysis and acid catalysed cyclization of 12-methoxydihydrocostunolide have also been described.