Total synthesis of (.+-.)-.ALPHA.-chamigrene and brominated chamigrene.

Total Syntheses of (±)-(Z)- and (±)-(E)-9-(Bromomethylene)-1,5,5-trimethylspiro[5.5]undeca-1,7-dien-3-one and (±)-Majusculone

“…In the synthetic sequence, some intermediates were produced as the isomeric mixtures, but the separations of them were shown to be unnecessary since all of the isomers could be eventually converted into either of the targets. In comparison with the previously reported syntheses (overall yields: 0.31% 6 and 4.51% 7 for 1, 2.12% 6 and 0.45% 7 for 2, respectively), the current study did not result in a significant improvement on the overall yields of 1 (0.85%) and 2 (1.74%), but the synthetic route developed by us appears to be more general and the generality has been demonstrated by the ready achievement of (±)-majusculone (3) from the intermediate leading to 1 and 2. The application of the same strategy for the syntheses of other members of chamigrene family is the focus of our ongoing studies.…”

“…In 1983, Iwata and co-workers reported the first total synthesis of 1 and 2 by using a copper-catalyzed cyclization of a phenolic a-diazo ketone to create the core structure (Scheme 1). 6 Following this, Niwa's group 7 described the second total synthesis by employing an acid-promoted spiroannulation of an enone aldehyde derived from anisole to construct the spirocyclic skeleton. In these synthetic routes, however, the key spirocyclic intermediates were produced either in a relatively low yield (22%) 6 or as an inseparable mixture with a tricyclic regioisomer.…”

“…6 Following this, Niwa's group 7 described the second total synthesis by employing an acid-promoted spiroannulation of an enone aldehyde derived from anisole to construct the spirocyclic skeleton. In these synthetic routes, however, the key spirocyclic intermediates were produced either in a relatively low yield (22%) 6 or as an inseparable mixture with a tricyclic regioisomer. 7 We herein wish to report the third total synthesis of (±)-1 and (±)-2 based on an approach to highly substituted cyclohexene system as recently developed by Liu's and our laboratories.…”

Halogenated Sesquiterpenoids from the Red Alga Laurencia tristicha Collected in Taiwan

“…The chemical constituents of marine red algae species of the genus Laurencia have been extensively investigated, and these algae have been found to be rich sources of halogenated sesquiterpenes, − diterpenes, ,− acetogenins, , and indoles. − Secondary metabolites discovered from these algae are predominantly sesquiterpenoids and are usually chlorinated or brominated. − In our continuing investigation of the chemical constituents of marine algae of this genus, L. tristicha was collected and studied in order to discover bioactive marine natural products from Taiwanese red algae. This study led to the isolation of 18 compounds, including eight new chamigrane-type sesquiterpenes ( 1 – 8 ) and one cuparane-type sesquiterpene ( 9 ), along with nine known compounds, halogenated chamigrene derivatives 9-( E )-bromomethylidene-1,5,5-trimethylspiro­[5.5]­undeca-1,7-dien-3-one ( 10 ) and 9-( Z )-bromomethylidene-1,5,5-trimethylspiro­[5.5]­undeca-1,7-dien-3-one ( 11 ), − ma’ilione ( 12 ), [1(15) Z ,2 Z ,4 S ,8 R ,9 S ]-8,15-dibromochamagra-1­(15),2,11 (12)-trien-9-ol ( 13 ), , [1(15) E ,2 Z ,4 S ,8 R ,9 S ]-8,15-dibromochamagra-1­(15),2,11­(12)-trien-9-ol ( 14 ), ,, ma’iliohydrin ( 15 ), isorigidol ( 16 ), , allo -isoobtusol ( 17 ), ,, and majusculone ( 18 ) . The structures of the compounds were determined on the basis of extensive spectroscopic analyses (IR, MS, 1D and 2D NMR) and by comparison of the spectroscopic data with those of related known compounds.…”