The structure of laurenene, a new diterpene from the essential oil of Dacrydium cupressinum. Part 2. Crystal structure

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

“…Laurenene ( 99 ) is a diterpene initially isolated by Corbett and co-workers in 1979 from Dacrydium cupressinum and contains the unique fenestrane motif (see Figure ). The tetracyclic [5.5.5.7]­fenestrane core was seen as a challenge that photocycloaddition chemistry was suited to address. , To generate the sterically crowded quaternary carbon center, a [2 + 2] photocycloaddition of enone 94 furnished the essential cyclobutane intermediate 95 in 87% yield and established the three contiguous quaternary centers required for the central core of laurenene ( 99 ). Further manipulations transformed cyclobutane 95 to the unsaturated keto ester 96 , where the cyclobutane underwent reductive ring opening under Birch reduction conditions (Na/NH 3 ) at −33 °C, followed by hydrogenation using Pd/C to afford keto ester 97 .…”

Carbon Flatland: Planar Tetracoordinate Carbon and Fenestranes

“…Beyond the synthetic, structural, and theoretical interest in the chemistry of fenestranes it is to be mentioned that Nature has provided us with laurenene 235 , a [5.5.5.7]fenestrene even containing a bridgehead double bond (Scheme ). − According to its X-ray structure the opposite bond angles are 117.9° and 118.9°. Epoxidation of 235 leads to 236 , a c , c , c , t -[5.5.5.7]fenestrane, which is readily converted into the ketone 237 with an all- cis fenestrane structure 18 …”

Laurenanes: Fenestranes with a Twist

“…4 The structure of lauren-1-ene was determined by X-ray analysis of a bromo derivative 2. 2 In the solid state, this compound existed in a conformation that avoided close interaction between the methyl groups at C-4 and C-9 by skewing the C-4 methyl toward the C-ring and the C-9 methyl toward the A-ring. This conformation, subsequently referred to as "skew 1", is illustrated in Figure 1 for the basic laurenane skeleton, a substituted [5.5.5.7]fenestrane.…”

“…Despite the fact that it was first reported over 20 years ago, , the naturally occurring diterpene, lauren-1-ene ( 1 ), remains the only known naturally occurring compound with an intact fenestrane ring system (rosettane) . Furthermore, it has only been isolated from New Zealand plant sources, initially from Dacrydium cupressinum and, more recently, from some Podocarpus species …”