Enrfo-cyclization

Reactions of 4-substituted 4-pentenyl bromoacetates with tri- -butylstannane resulted in modest yields of eight-membered enrfo-cyclization products, along with reduction products." ... 

Dieb-Alder catalyst. The key step in a recent total synthesis of androstanes is a SnCVcatalyzed Diels-Alder reaction of 1 with the (Z)-dienophile 2. The geometry of the diene favors addition ami to the C,0-methyl group, and the catalyst promotes the desired enrfo-orientation. A1C1, and BF3 ctherate are less suitable for additions involving aliphatic bifunctional dienophiles. The initial adduct a can be isolated, but in only 15-20% yield. The synthesis of the androstane 4 is completed by ketalizatioh of 3 followed by a novel cyclization affected with dimsylsodium. ... 

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. ... 

Having established an optimum set of conditions for 5-enrfo-trig iodocyclizations of homoallylic alcohols, we carried out model studies to ascertain the scope and limitations with regard to substitution patterns of both the alcohol and alkene functions <99JCS(P1)2143>. In summary, most types of ( )-homoallylic alcohols undergo smooth and stereoselective S-endo cyclizations to give excellent yields of the iodotetrahydrofurans 27-31, 33 and 34. 

Cyclization of 2-but-3-enylcyclohexanes mediated by zinc in the presence of trimethylsilyl chloride may also be influenced by the same controlling factors. Corey reported [12] that c -2-but-3-enyl-4-f-butylcyclohexane gave mostly an enrfo-methyl-cw-hydrindanol. The 1,5-cis/trans ratio was reported to be 66 7. 

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