Bicyclo octenes

Scheme 2.201. Synthesis of c/s-bicyclo[3.3.0]octenes via domino carbolithiation/ electrocyclization/electrophile trapping.

Ring-opening was not restricted just to norbornenes bicyclo[3.3.0]octenes, cyclooctene and a functionalised cyclobutene were all reactive substrates for these reactions. 

Fig. 3. The thermal isomerization of 1,1-dicyclopropylethylene. (X) axis Time in minutes (Y) axis Percentage yield o 1,1-dicyclopropylethylene 0, 1-cyclopropyl-cyclopentene 0, bicyclo[3,3,0]octene-l.

The bicyclo[3.3.0]octene skeleton is of interest due to its potential use as an intermediate in the synthesis of cyclopentanoid natural and nonnatural compounds. The bicyclo[3.3.0]octene skeleton can be prepared by asymmetric elimination of the corresponding alcohols on treatment with a variety of chiral amines80, S1. Bicyclic trifluoromethanesulfonales 1 on treatment with (5)-Ar,Ar-dimethyl-l-phenylethylaminc give the corresponding bicyclo[3.3.0]octenes 2 with 15,5/ -configuration with up to 89% enantiomeric excess in high yield. 

Cylindramide (90) is a cytotoxic compound isolated from Halichondria cylindrata (7.10 s % wet wt.), but very likely of bacterial origin [148]. The structure was deduced from spectroscopic analysis, the relative stereochemistry (only) of the bicyclo[3.3.0]octene unit by NOESY techniques, and the absolute stereochemistry of the amino acid of the tetramic acid ring (25,35) from the recovery of erythtro-L-(3-hydroxyomithine from oxidative degradation of 90. It showed cytotoxicity to B16 melanoma cells (IC50 0.8 (ig/ml). 

Williams and Reeves138 developed a powerful cascade reaction process for the construction of functionalized cA-bicyclo[3.3.0]octenes. Carbolithiation of 3-methylene-1,4-cyclooctadiene 227 with 1°, 2° or 3° alkyllithium reagents leads to cyclooctadienyl anions,... 

A number of papers have been published describing the thermal isomerization reactions of bicyclo[2.2.2]oct-2-ene, bicyclo[3.2.1]oct-2-ene, and norcamphene to bicyclo[3.3.0]octenes.149-152 The gas phase and solution phase isomerization of perhydroindane to a mixture of methyl substituted bicyclo[3.3.0]octanes has also... 

An important field of application of the 1,3-elimination method concerns those compounds where oxiranes can be obtained with configurations opposite to those of the oxiranes resulting from the peracid method. Examples are the stereoselective epoxidation of a methylenecyclohexane derivative with NBA/KOH, the epoxida-tion of 3-alkylcyclopentene and 3,4-dialkylcyclopentene with NBS/KOH, and the /3-epoxidation of bicyclo[3.3.0]octene and bicyclo[4.3.0]nonene. The different stereoselectivities can be interpreted on the basis of the mechanisms of the... 

Carboxylatiou (1, 406-407). m-Bicyclo[3.3 OJoctane-1 -carboxylic acid (2) can be prepared1 conveniently in about 25% yield by treatment of ra-bicyclo[3.3.0]octene-2... 

Cycloocta-1,5-dienes undergo various metal-mediated conversions to bicyclic and polycyclic carbon skeletons, e.g. bicyclo[3.3.0]octenes. In the presence of nickel catalysts tricy-clo[5.1.0.0 ]octanes are produced. " ... 

Potassium fluoride in a two-phase system was also efficient when 18-crown-6 was present as a phase-transfer catalyst. The desilylation by fluoride produced a 7-0x0 enolate which could be reacted with various electrophiles. Appropriately substituted bicyclo[3.1.0]hexane derivatives 42 and 44 have been used to study this reaction.a,/l-Unsaturated carbonyl compounds gave rise to the formation of Michael adducts, while treatment with triphenylvinylphos-phonium salts gave bicyclo[3.3.0]octenes 46 as the result of a subsequent intramolecular Wittig reaction. 

Potassium hydride is superior to phenylsodium, phcnylpotassium, or potassium for isomerization of cyclooctadienes to c/s-bicyclo[3.3.0]octene-2.1 Potassium... 

Grieco and coworkers have utilized intramolecular aldolization of keto aldehydes to form seven-mem-bered rings. In a synthesis of ( )-helenalin, keto aldehyde (54) was cyclized to aldol (55 equation 1In a later modification of the basic approach, keto aldehyde (56) was cyclized to cycloheptenone (57 equation 113).The success of these cyclizations is related to the fact that the normally preferred five-membered ring closure would yield a strained rnzns-fused bicyclo[3.3.0]octene system. 

Hydropentalenes (bicyclo[3.3.0]octanes) are not very common in nature. Therefore, few studies have dealt with the hydrogenation of bicyclo[3.3.0]octenes. However, fused five-membercd rings form the skeleton of the tricyclic triquinanes. Furthermore, in all natural products of the triquinane type, the fusion of the five-membered rings is exclusively cis. 

In the presence of Ni(cod)2-TMEDA, certain 2-alken-7-ynones are transformed into bicyclo[3.3.0]octenes or bicyclo[3.1.0]hexanes, depending on whether an electrophile is added. ... 

Compounds in this category are bicyclo[3.3.0]octene (15), tricyclo[5.2.1.0 ]dec-3-ene (16), exo-tricyclo[5.2.1.0 ]dec-8-ene (17), benzvalene (18), and delta-cyclene (19). Of these, 15 and 16 do not undergo ROMP with conventional catalysts (Ofstead 1972), but 17 does so (Oshika 1968). The ROMP of 18 proeeeds smoothly using tungsten carbene initiators, and films of the polymer 18P can be cast directly from the reaction mixture (Swager 1988, 1989). The polymer has a tendency to cross-link and to decompose spontaneously once isolated in dry form, so is best handled in solution, especially as the decomposition can be explosive. The DSC thermogram of the polymer shows an exotherm at 153°C, attributed mainly to isomerization to polyacetylene 20, eqn. (3), and a second exotherm at... 

The Pauson-Khand reaction is also mediated by complexes of other transition metals including those of titanium, rhodium and iridium. A number of complexes of these metals have been used to catalyse the intramolecular asymmetric Pauson-Khand reaction of 1,6-enynes to give bicyclo [3.3.0] octenes. The... 

RRM processes can also be coupled with an additional CM event Such a scenario is depicted for a norbornene derivative in Scheme 2.18 [12a]. Domino ROM/RCM of 45 with the first-generation Gmbbs catalyst 1 in the presence of terminal olefin 46 yielded the bicyclic enone 47 as a 2 1 mixture of separable ( )- and (Z)-diastereomers. Subsequently, (E -47 was successfully advanced to the cytotoxic macrolactam (-l-)-cylindramide A in a straightforward manner. The enantiopure norbornene 45 was also used in a domino RRM/CM approach to the bicyclo[3.3.0]octene core of the macrolactam geodin A [12b]. 

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