| Ruthenium catalyzed olefin metathesis is a methodology in organic synthesis which has enjoyed an explosion of interest over the last decade. Application of this technology in the preparation of various fused ring systems is reviewed in depth, and the methodology has been explored as approaches to three specific ring systems: First, both cis- and trans-delta-2-octalins can be produced readily by ring closing metathesis in the presence of the Grubbs catalyst (bis(tricyclohexylphosphine) benzylidine ruthenium(IV) dichloride) ( A) and/or the SImes catalyst (tricyclohexylphosphine[1,3-bis(2,4,6-trimethlyphenyl)-4,5-dihydroimidazol-2-ylidine][benzylidine]ruthenium(IV) dichloride) (B). For cases where the olefinic moiety of the substrate is disubstituted, catalyst B is required. It appears that the reaction of trans substrates is somewhat more facile than that of the corresponding cis isomers. The stereochemistry of 1,2-diallyl-1,2-cyclohexanediols and that of 9,10-dihydroxy delta-2-octalins can be assigned by examination of the 1H NMR spectra. Second, a domino ROM/RCM/RCM was explored as an approach to preparation of trans-syn-trans ring systems typified by natural products such as Brasilicardin A. Preparation of two model compounds demonstrated the limitations of this methodology, which stem from the reluctance of a cis-fused bicyclo[4.4.0]decene ring system to undergo the key ring opening metathesis step. Third, preparation of an appropriately functionalized enyne metathesis substrate allowed a tandem enyne metathesis reaction that provided the unique 5-7-6 ring system present in the Guanacastepene family of natural products. While the symmetrical substrate 5,8-diethynyldodeca-1,11-diene-5,8-bis-triethylsiloxane undergoes metathesis to give an undesired bis-vinylcyclopentene product, addition of steric bulk to one of the pendant olefins (e.g. 5,8-diethynyl-12-methyltrideca-1,11-diene-5,8-bis-triethylsiloxane) promotes unidirectional reaction, which gives the desired tricyclic framework. |
