Propellane sesquiterpenes

Turning now to the intriguing propellane sesquiterpene modhephene (308), Karpf and Dreiding159 have provided full details of their original synthesis. Hot... 

The formal synthesis of the propellane sesquiterpene natural product modhephene (168) was... 

The pentalenone 6 is an intermediate in the synthesis of 3.3.3. propellane sesquiterpenes like modhephene. But, again, poor yields were observed by Paquette in the multi-step synthesis of by acylation of cyclopentene or 1-trimethylsilylcyclopentene and cyclization of the corresponding divinyl-ketone. 41,42 Moreover, two isomeric pentalenones were obtained and it was necessary to isomerize with rhodium trichloride. 

Cuprate conjugate additions. One step in a recent synthesis of (-t-)-modhephene (3). a natural sesquiterpene with a (3.3.3)propellane skeleton, involved conjugate addition of lithium dimethylcuprate to 1. The desired reaction proved difficult... 

Intrtimolecular exocyclic transannular cycloaddition of TMM can provide a viable route to propel-lanes, such as the sesquiterpene modhephene (144). This methodology is demonstrated in an efficient synthesis of a [3.3.3]propellane (145) (equation 149). The methylenecycloptt ane approach is preferred in this case because it works well with dialkyl-substituted systems. 

A six-step synthetic approach to the tetracyclic skeleton of neurotrophic sesquiterpene merrilactone A, using intramolecular photocycloaddition to form the oxetane ring, was reported.902 Irradiation of a degassed acetonitrile solution of 262 gave the product 263 (Scheme 6.108) in a very high yield (93%). This reaction creates three stereocentres in two new rings, forming an oxa[3.3.3]propellane framework. 

Mehta, G. and Subrahmanyam, D., Photochemical oxa-di-Jt-methane rearrangement approach to [3.3.3]propellanes. Total synthesis of sesquiterpene hydrocarbon ( )-modhephene,/. Chem. Soc., Perkin Trans. 1, 395, 1991. 

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