Quinanes synthesis

The observation of a stereoconvergent cyclization by Roy et al. [18], as shown in the third example, is of special interest from a synthetic point of view because it exploits the configurational lability of radicals in a favorable manner. The other examples, i. e. Nugent and RajanBabu s cyclization of a carbohydrate-derived epoxide [5d] and Clive s quinane synthesis [19], amply demonstrate the usefulness of the titanocene-initiated epoxide opening. 

Hudlicky developed a general method of tiiquinane synthesis based chi a cyclopropanation- arrange-ment sequence of dienic diazo ketones (Scheme 52). Topological selectivity of linear versus angular tri-quinane synthesis has been achieved. ... 

An elegant strategy for the synthesis of fused cyclopentanoids has been reported by Marino and coworkers (Scheme 21).38 Reaction of (104) with the phosphonium salt (105) generated the bicyclic system (106). Further conversion of (106) to (107) enabled the annulation sequence to be repeated to form tri-quinane derivatives such as (108). 

V K. Singh, B. Thomas, Recent Developments in General Methodologies for the Synthesis of Linear Tri-quinanes, Tetrahedron 1998, 54, 3647-3692. 

Transannulation of the mesylate (33), derived from 4,8-dimethylcycloocta-4-en-l-ol, using sodium carbonate in aqueous dioxane has provided the bicyclo[3.3.0]octanol (34), a central precursor to the monoterpene iridomyrmecin (35 equation 13). In studies of the biomimetic synthesis of the natural tri-quinanes capnellene (37 equation 14) and pentalenene (40 equation IS) Pattenden et al. have shown that both molecules can be produced from appropriate cycloocta-l,S-diene precursors, i.e. (36) and (39) [or indeed their corresponding positional isomers (38) and (41), respectively] by treatment with boron trifluoride. Mehta et al. have described an alternative transannulation approach to the triquinane unit found in pentalenene, i.e. (42) - (43 equation 16), and also to the ring system (44 equation 17) found... 

Irradiation of the enone (80) at 282 nm brings about the formation of the oxetane (81), and this process has been used as a key step in the development of a synthesis of 2,7,9-trimethylenetricyclo[4.3.0.0 ]non-4-ene. Such intramolecular additions are popular methods for the formation of polycyclic compounds that can be used as starting materials in syntheses. An efficient example of this from earlier years is the formation of the oxetane (82,90%) from the intramolecular cyclization of the enone (83). The oxetane formed is a key intermediate in a new efficient route to enrfo-hirsutene. ° A review of the application of the Diels-Alder/Patemo-Buchi reaction as an approach to di- and tri-quinanes has been published. ... 

Wender and co-workers continue to make elegant synthetic use of the intramolecular meta photocycloaddition of phenyl-ethenyl non-conjugated bichromophoric systems and this year describe three such applications of the reaction. The synthesis of ( )-silphinene (40), the first member of a new family of tri-quinane natural products, has been achieved in three steps and... 

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